225d Hyd Sys

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Product: EXCAVATOR

Model: 225D EXCAVATOR 2SJ

Configuration: 225D EXCAVATOR 2SJ00001-UP (MACHINE) POWERED BY3208 ENGINE

Systems Operation225D, 229D & 231D EXCAVATORS HYDRAULIC SYSTEMMedia Number -SENR4269-01 Publication Date -01/06/1991 Date Updated -11/10/2001

Systems Operation

Introduction

Reference: For illustrated Specifications, make reference to the Specifications For 225D,

229D And 231D Excavators Hydraulic System, Form No. SENR4268. If the

Specifications given in Form SENR4268 are not the same as given in the Systems

Operation and the Testing And Adjusting, look at the printing date on the back cover of

each book. Use the Specifications given in the book with the latest date.

Schematic Of Pump Flow And Pressure

Control

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(15) Filter For Pilot System.

(16) Pilot (Gear-Type) Pump. The oil supply for the pilot system comes from this pump.

(17) Bent-axis Piston Pump (Front). This is a variable displacement pump. It supplies the main oil flow to

operate the right track motor, the bucket cylinder, the boom cylinders and when the stick crossover valve is

activated, the stick.

(18) Bent-Axis Piston Pump (Rear). This is a variable displacement pump. It supplies the main oil flow to

operate the swing motor, the left track motor, the stick cylinder and when the boom crossover valve is

activated, the boom.

(19) Combiner Valve For Main System Oil. The individual check valves do not allow the flow of oil from

variable displacement pumps to combine (go together) except when the pressure on both pumps reaches

relief valve pressure.

(20) Relief Valve For Main System Pressure. This valve limits the pressure of the main system oil to 29

650 kPa (4300 psi). When the pilot valve for machine travel or the switch for increased pressure is

activated, this valve limits the system pressure to 31 700 kPa (4600 psi) for the 225D and 33 100 kPa (4800

psi) for the 231D only. System pressure for machine travel on the 229D is limited to 29 650 kPa (4300 psi).

Pump Flow And Pressure Control

Introduction

Double Pump (Bent-Axis Piston)

The 225D, 229D and 231D Excavators have two primary hydraulic pumps along with a

common control system combined into one housing with one input drive shaft. Pumps(17) and (18) are variable displacement and bent-axis piston type. The pump housing is

bolted directly to the flywheel housing.

A mechanical connection between pumps (17) and (18) makes sure they always have the

same displacement. The maximum output of each of the pumps is approximately:

225D ... 212 liter/min (56 U.S. gpm)

229D, 231D ... 235 liter/min (62.3 U.S. gpm)

The maximum working pressure of each pump circuit (implements) is limited by relief valve (20) to 29 650 ± 345 kPa (4300 ± 50 psi) for implement operation.

For the track circuit, system pressure of each pump circuit is limited to 31 700 ± 345 kPa

(4600 ± 50 psi) for the 225D, 29 650 ± 345 kPa (4300 ± 50 psi) for the 229D and 33 100

± 345 kPa (4800 ± 50 psi) for the 231D.

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Hydraulic Pumps (Typical Example)

(16) Pump (pilot). (17) Pump (bent-axis piston) (front). (18) Pump (bent-axis piston) (rear).

Hydraulic Pumps

(16) Pump (pilot). (17) Pump (bent-axis piston) (front). (18) Pump (bent-axis piston) (rear).

The output flow of the two bent-axis piston pumps is used to:

1. Operate the hydraulic cylinders of the implements (boom, bucket, stick andattachments).

2. Operate the track motors that move the machine in FORWARD and REVERSE.

3. Turn the swing motor that gives rotation to the upper structure.

The output (horsepower) of the engine in the excavator is used to turn the two bent-axis

piston pumps and a pilot pump at the same speed as the engine. The horsepower neededto operate the hydraulic system when both bent-axis piston pumps are a maximum

pressure is approximately 2.3 times the maximum horsepower available from the engine.

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Such an overload condition is not possible because of the oil pressure summing control

system for the pumps. The control system automatically regulates the output of the piston pumps. It sums the oil pressure from each pump to control pump displacement (output).

Pilot Pump

In addition to the two bent-axis piston pumps used to power the implements and tracks,

there is a small gear pump (16) mounted on the double pump housing. It is driven by a

gear arrangement (in the housing) at the same rpm as the engine. This pump sends oil to

the pilot system. The pilot system is used to move the spools in the main control valvesfor implements and track. The pilot system also causes the release of the parking brakeswhen a travel pedal is pushed down.

System Components And Oil Flow

Front And Rear Main Control Valves (Earlier Style Shown)

(1) Control valve (right track). (2) Control valve (bucket). (3) Control valve (boom). (4) Control valve

(boom and stick crossover). (5) Control valve (stick). (6) Control valve (left track). (7) Control valve

(swing). (21) Overspeed valves (right track). (22) Overspeed valves (left track).

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Rear Main Control Valve (Earlier Style Shown)

(4) Control valve (boom and stick crossover). (5) Control valve (stick). (6) Control valve (left track). (7)

Control valve (swing). (22) Overspeed valves (left track).

When all of the main control valves are in NEUTRAL, output oil from front pump (17)

goes through control valve (1) for the right track, control valve (2) for bucket, controlvalve (3) for the boom and control valve (4) for boom and stick crossover. From valve (4)

it returns to tank through the implement system filter. Output oil from rear pump (18)

goes through control valve (7) for the swing, control valve (6) for the left track, control

valve (5) for the stick, and control valve (4) for boom and stick crossover. From valve (4)it returns to tank through the implement system filter.

Combiner (19) and relief valve (20) control the flow and pressure in the circuits of thetwo bent-axis piston pumps (17) and (18). Check valves in the combiner valve keep the

flow from the two pumps separate. If the pressure in both circuits becomes as high as the

opening pressure of relief valve (20), the flow from both pumps will go back to tank

through the relief valve.

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The double pump system incorporates a summing valve as an integral part of the double

pump. The summing valve provides a regulating signal pressure based on output pressurefrom the two pumps.

Pilot system oil from pilot pump (16) goes through filter (15) to relief valve (14) for the

pilot system. All of the control valves in the pilot system are closed in the NEUTRAL position. Oil flow from pump (16) fills the lines and valves in the pilot system. The oil

pressure increases to the setting of relief valve (14). Relief valve (14) is set at 2300 kPa

(335 psi) system pressure. All of the oil flow from pump (16) goes through relief valve

(14) and back to tank when the pilot valves are in NEUTRAL.

Double Pump

(Bent-Axis Piston)

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Cross Section Of Bent-Axis Piston Pump (Top View)

(1) Housing. (2) Shaft (front pump). (3) Retainer plate. (4) Pin (pivot). (5) Piston (seven). (6) Barrel

assembly. (7) Port plate. (8) Outlet (front pump). (9) Head. (10) Inlet (suction). (11) Actuator assembly.(12) Shaft (rear pump). (13) Piston (seven). (14) Barrel assembly. (15) Outlet (rear pump).

The bent-axis piston type double pump is a variable displacement pump located at therear of the engine. The term bent-axis refers to the angular movement (8° to 25°) of the

piston pump assembly about the point of intersection (axis) of center lines (16) and (17).

Shaft (12) (of the rear pump) is driven by the engine flywheel. Besides directly drivingthe rear pump, shaft (12) drives shaft (2) for the front piston pump; and idler gear (18) for

the pilot pump (mounted on the double pump housing).

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All pumps rotate at the same rpm as the engine. Both the piston pumps are mechanically

linked together by the fork of actuator assembly (11) so that both pump displacements arealways the same. The implement and motor circuits for each pump are normally separate.

Therefore, circuit pressures are generally not the same and either pump can send oil to itsrespective circuits at any pressure between zero and relief valve pressure. Both piston

pumps are located in housing (1) and use the oil supplied to inlet (10) from the hydraulic

tank.

Double Pump

(1) Housing. (9) Head. (10) Inlet.

When the engine is running, shaft (12) turns seven pistons (13) (of the rear pump) which

in turn rotate their barrell assembly (14). Shaft (12) also drives shaft (2) which in turn

rotates seven pistons (5) (of the front pump). Pistons (5) rotate their barrel assembly (6).

Each barrel assembly has a center pin (4) on which it pivots.

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225D Shown (Without Increased Pressure) Pump Housing (Side View)

(2) Shaft (front pump). (3) Plate. (4) Pin (pivot). (12) Shaft (rear pump). (13) Piston (seven). (14) Barrel

assembly. (16) Center-line (shafts). (17) Center-line (pumps). (18) Idler gear for pilot pump. (A) Direction

for pump destroke. (B) Direction for pump stroke.

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Double Pump Head

(8) Pump outlet. (9) Head. (15) Pump outlet. (19) Port (inlet). (20) Port plate (front pump). (21) Port plate

(rear pump). (22) Port (outlet) (rear pump). (23) Port (outlet) (front pump).

Each gear has a retaining plate (3) which retains the piston heads while allowing them to

swivel in their sockets.

Double Pump Barrel Assemblies

(3) Retainer plates. (6) Barrel assembly (front). (14) Barrel assembly (rear). (24) Cylinders (fourteen).

Oil from the hydraulic tank goes into head (9) of the pump at inlet (10). The oil goes

through passages in head (9) and then through inlet ports (19) of port plates (20) and (21).

The oil then enters the cylinders [of barrel assemblies (6) and (14)], which are positioned

over inlet ports (19). As the barrel assemblies turn, cylinder openings (24) in each barrel

rotate in turn to the position of inlet ports (19).

Pump Stroke

Each port plate (20) and (21) moves in its own machined track (groove) (25) which has a

circular contour. Track (25) allows 8° to 25° angular movement of each port plate and its

respective rotating barrel assembly. By moving in radial direction (B), the port platesincrease the angle of the barrel assembly which increases the stroke (displacement) of the

pistons. This in turn increases output from the pump. By moving in radial direction (A),

the port plates decrease the angle of the barrel assembly which decreases the stroke of the

pistons.

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Pump Head (Port Plates Not Shown)

(8) Passage (front pump output). (10) Passage (inlet). (11) Actuator assembly. (15) Passage (rear pump

output). (25) Track. (26) Pump regulator valve. (A) Direction for decreased pump stroke. (B) Direction for

increased pump stroke.

Both port plates move the same amount at the same time because of their mechanical link with the fork of actuator assembly (11). The piston of actuator (11) moves according to

signal pressure from the summing valve. (See Summing Valve and Pump Regulator

Valve section).

As mentioned above, each of the fourteen pistons changes its stroke (displacement),

depending on the angle of its port plate. As the pistons follow the angle of the port plate,

they move in and out of their respective cylinder openings in the barrel cylinder. As the piston moves out of the barrel cylinder, it pulls oil in behind it from passage (10). The oilthat is pushed ahead of the piston goes through outlet ports (23) and (22) of port plates

(20) and (21) respectively. The oil then leaves the pump through passages (8) and (15)

and goes to the circuits.

Outlet ports (23) and (22) have struts between them for added strength. Inlet oil is sealed

from outlet oil by a metal-to-metal seal between the face of the port plate and the face of the barrel. On the other side of the port plate, the seal is made with the face of the

machined track. Since outlet pressure can be as high as 33 100 kPa (4800 psi), the sealing

faces must be made with precision and no damage is permissible. Protection must be

given to these faces during disassembly and assembly.

Pilot Pump

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Pilot Pump

(1) Housing. (27) Gear pump.

Pump Drive System

(2) Shaft (front pump). (12) Shaft (rear pump). (18) Gear (idler). (28) Drive shaft (pilot pump).

In addition to the two bent-axis piston pumps used to power the implements and track,

there is a gear-type pump (27). Pump (27) is mounted on double pump housing (1). It is

driven by drive shaft (28) which is driven by an idler gear (18). Gear (18) is driven by

rear pump drive shaft (12). Pump (27) is driven at an rpm that is the same as the rpm of

the engine. When there is a decrease in the engine rpm, there is also a decrease in the rpm

and output of the pump.

Pump Control System

Introduction

The excavator system is designed to operate with the governor control setting on

maximum engine speed (rpm). If both bent-axis pumps were to work at full output and

maximum pressure, the horsepower needed would be more than is available from the

engine. To prevent an engine stall, a control system made up of summing valve (2),

actuator assembly (5), lever assembly (26) and pump regulator valve spool (18) regulates pump displacement so that there is a decrease in the output of the two piston pumps. In

this way, the control system makes sure that the power needed to operate the hydraulicsdoes not exceed power available from the engine.

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Double Pump Head Assembly

(1) Head assembly. (2) Summing valve. (3) Output (rear pump). (4) Output (front pump). (5) Actuator

piston. (6) Maximum pump angle adjustment.

Double-Pump Head Assembly (Port Plate Side View)

(1) Head assembly. (2) Summing valve. (4) Output (front pump). (5) Actuator piston. (18) Spool (pump

regulator valve). (26) Lever assembly.

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Under constant power limiting conditions (pump displacement other than maximum

displacement), spool (9) of the pressure summing valve is positioned by hydraulic forcesso that metering areas (10) and (11) are slightly open. This condition allows a slight flow

of output pressure oil from the pump(s), through respective check valve(s) (7) and (8)into summing pressure cavity (17). The amount of this flow is just enough to make up the

small amount of oil that leaks past the pump regulator valve located in actuator piston (5).

Check valve (7) or (8) that does not open, prevents oil from both pressure summing

cavity (17) and the other open check valve (8) or (7) from flowing back into the pumpingunit that is operating at a lower discharge pressure.

If either output pressure rises when spool (9) is in the centered position, the opposing

forces on the spool become unequal and the spool will shift to the right. This shift

increases both metering areas (10) and (11) which increases the flow to check valves (8)

and (7) respectively. One of the pump output pressures must be higher than the output

pressure of the summing valve. The respective check valve will open further to allow anincrease flow of output pressure oil into cavity (17).

Summing Valve

(2) Summing valve. (5) Actuator piston. (9) Spool.

This increases the summing pressure until the summing pressure is high enough to shift

spool (9) back to the left, reducing the metering areas to the steady state (unchanging)

condition described above. If either output pressure decreases when spool (9) is in the

centered position, the opposing hydraulic forces become unequal and the spool will shift

to the left. This shift completely closes both metering areas (10) and (11) to stop any flowof pressure into pressure summing cavity (17). The pump regulator valve has some

leakage, so oil is continuously being removed from the pressure summing cavity. As aresult, the summing pressure will decrease slightly with time. When the pump regulator

valve (see next section) feels the slight decrease in summing pressure, it changes position

to allow pump displacement to increase. As the pump regulator valve allows pump

displacement to increase, the summing pressure decreases. When the summing pressure

has decreased sufficiently, the summing valve spool moves to the right to its steady state

position.

All loads do not cause a large enough pressure increase on the system to cause a decrease

in pump displacement. For example, the activation of the swing circuit does not normally

cause a load that is high enough to change pump output.

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225D Shown (Without Increase Pressure) Double Pump Control System (Pumps At Maximum

Displacement)

(1) Head assembly. (5) Actuator piston. (18) Spool (pump regulator valve). (19) Sleeve (pump regulator

valve). (21) Spring. (22) Adjustment screw (horsepower). (23) Adjustment screw (torque slope). (24)

Spring. (25) Small end (actuator piston). (26) Lever assembly. (27) Passage. (28) Passage. (29) Actuator

chamber. (30) Pump (rear). (A) Distance (to lever fulcrum).

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Pump Head

(20) Port plates.

Only one pump regulator valve is used to control the displacement of both pumps. This is

possible because port plates (20) of both pumps are connected mechanically to actuator

piston (5). This forces both pumps to always be at the same displacement. [See DoublePump (Bent-Axis Piston section)].

The displacement actuating arrangement used in the pump group makes the pump always

want to get to its maximum displacement when there is no actuator pressure in chamber (29). This is done by use of spring (24) and the hydraulic force of summing oil pressure

against small end area (25) of actuating piston (5).

The displacement of both pumps is controlled by regulating the amount of oil in actuating

chamber (29). When oil is added to chamber (29), pump displacement decreases. When

oil is vented from chamber (29), pump displacement increases.

Pump Regulator Valve Operation

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Pump Regulator Valve (Pumps At Maximum Displacement)

(5) Actuator piston. (18) Spool. (26) Lever assembly. (27) Passage. (28) Passage (to actuating chamber).

(31) Passage to case. (32) Passage. (33) Passage. (34) Differential area. (38) Differential area. (B) Force of lever assembly.

The pump regulator valve controls the amount of oil in chamber (29) based on summing

oil pressure and pump position (displacement). Summing oil pressure is routed through

drilled passage (27) of actuator piston (5) to passage (32) of sleeve (19). Since

differential area (34) is slightly larger than differential area (38), oil flows around spool(18) and exerts pressure against differential area (34) to maintain spool (18) in contact

with lever assembly (26). When the summing pump oil pressure increases (refer toMachine Configuration Chart in the Testing and Adjusting section for pressure values), it

forces spool (18) to move against force (B) of the lever assembly and start compressing

spring (21). At the same time, passage (33) opens to allow summing oil pressure to

chamber (29) through passage (28). With a further increase in summing oil pressure, the

pressure in chamber (29) goes from tank to approximately 4500 kPa (650 psi) and

overcomes the force of summing oil pressure on the small end area (25) of piston (5) and

spring (24). This is the start of the power limiting condition.

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until spool (18) moves enough to start metering a limited amount of pressure oil to the

pump case sump through passages (28), (33) and (31).

As pump oil pressure decreases, summing valve spool (9) moves to the left to stop flow

through the summing valve. Summing oil pressure leakage past spool (18) decreases the

force on differential area (34). This allows spool (18) to move further to the right anddump pressure in chamber (29). Piston (5) then moves down, which increases pump

displacement to maximum.

If summing oil pressure reaches the main relief valve setting (see Hydraulic Pump

Operation, Introduction), actuator piston (5) will have decreased pump displacement to

approximately 8°. Engine speed should remain at 2005 to 2060 rpm for the 225D and

2205 to 2260 rpm for the 229D and 231D (see Hydraulic Pump Operation, Introduction)during pump regulation.

NOTE: When there is oil pressure in chamber (29), engine speed should not vary more

than 5 rpm. If constant engine speed cannot be maintained, the power screw or torque

screw located on the pump will need to be adjusted. Refer to Testing and Adjusting

section in this manual for proper adjusting procedures.

Lever Assembly

Lever Assembly And Actuator Piston

(5) Actuator piston. (18) Spool. (19) Sleeve. (26) Lever assembly.

Lever assembly (26) determines the power characteristics of the pump. Adjustment screw

(22) determines when destroking begins. Adjustment screw (23) determines the pressure/flow relationship of the pumps.

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225D Shown (Without Increase Pressure) Double Pump

(5) Actuator piston. (18) Spool. (21) Spring. (22) Screw. (23) Screw. (26) Lever assembly. (35) Pin. (36)

Slot. (37) Pin. (B) Force.

When turned clockwise (CW), screw (22) compresses spring (21). In turn, spring (21)

applies more force (B) against the end of lever (26) which pivots about pin (35). More

pump oil pressure is now needed to move spool (18) so that destroking can take place.

When pressure increases enough, power regulator valve spool (18) moves to the end of

lever (26) and its slot (36) until slot (36) is stopped by pin (37). Destroking begins at this point. Turning adjustment screw (22) counterclockwise (CCW) reduces the pump

pressure needed to move lever (26).

When adjustment screw (23) is turned CW, pin (35) (pivot point from the lever) moves tothe right. This increases the pump oil pressure needed to move pump regulator valve

spool (18) and actuator piston (5) up when destroking. Turning screw (23) CCW will

decrease pump pressure needed for destroking.

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Pump Actuator Hydraulic Stroke Limiter: 225D - 229D

(Attachment), 231D (Standard)

The actuator (stroke limiter) is used to limit the output of the double pump in machines

with the increased pressure circuit and/or hammer circuit attachments. This attachment ismounted on the pump in place of the standard cover.

225D (Earlier Style Shown) Actuator Group (Stroke Limiter)

(1) Piston. (2) Spacer (hammer system only). (3) Actuator. (4) Head Assembly. (5) Piston. (6) Passage.

Hydraulic Hammer System

The actuator in the hammer attachment is the same as for the increased pressure circuitwith the exception of spacer (2). When the trigger is pressed in, a solenoid energizes to

allow pilot oil to enter passage (6) and move piston (5) up. In the hammer circuit, spacer

(2) keeps piston (5) from traveling its full stroke. Piston (5) pushes piston (1) up to

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destroke the pumps and reduce the output flow for proper hammer operation. In the

hammer circuit the main relief valve setting remains at its normal setting.

Increased Pressure System: 225D - (Attachment), 231D - (Standard)

Right Hand Console

(7) Switch.

When electrical switch (7) is moved to the right, solenoid valve (8) energizes to allow pilot oil to enter passage (6) and move piston (5) up. Piston (5) pushes piston (1) up to

destroke the pumps and reduce output flow. With this reduced output flow, the machine

implement and track functions will be slower. However, when the switch is moved to theright and solenoid valve (8) opens, pilot oil changes main relief valve (10) setting for the

225D to the 31 700 ± 345 kPa (4600 ± 50 psi) track relief setting, for the 231D to the 33

100 ± 345 kPa (4800 ± 50 psi) track relief setting. This increases the pump output

pressure capability.

Increased Pressure Signal Valve

(8) Valve (solenoid). (9) Line (signal to main relief valve). (10) Valve (main relief).

Main Relief And Combiner Valves

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229D Shown Cross Section Of Main Relief And Combiner Valve

(4) Main relief valve. (5) Chamber. (6) Valve. (7) Orifice. (8) Passage for oil flow from the front pump. (9)

Combiner valve. (10) Passage for oil flow from the rear pump. (11) Pilot valve. (12) Shims. (15) Outlet to

tank. (16) Check valve. (17) Check valve.

229D Shown Main Relief And Combiner Valve

(11) Pilot valve. (16) Check valve. (17) Check valve.

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Combiner valve (9) makes it possible to use only one main relief valve to limit the oil

pressure in both pump circuits. The combiner valve also keeps the two circuits separate.An oil line connects the front pump to passage (8) and an oil line connects the rear pump

to passage (10). Oil lines take the flow from passages (8) and (10) to the main controlvalves. If a control valve is moved to activate the right track motor, or the bucket or

boom cylinders, an increase in pressure in passage (8) will open check valve (16) and

relief valve (4) will feel the pressure in the circuit coming from the front pump. The

spring will hold check valve (17) closed. If a control valve is moved to activate the lefttrack or swing motors or the stick cylinder, the pressure will increase in passage (10)

from the rear pump. If the load in passage (10) (rear pump circuit) causes the oil pressure

in passage (8) (front pump circuit), check valve (17) will open and check valve (16) will

close. Main relief valve (4) will, at all times, feel the pressure of the pump circuit that has

the highest oil pressure.

The oil to main relief valve (4) goes through orifice (7), chamber (5), through and around blocker valve (3) to pilot valve (11). If the oil pressure in either passage (8) or (10)

becomes higher than 29 650 kPa (4300 psi) pilot valve (11) opens. This causes the pressure in chamber (5) to decrease. Oil pressure moves valve (6) to the left and lets oil

go to tank through outlet (15).

Travel Main Relief - 225D And 231D

When either direction control valves (foot pedals) are pushed down, pilot system pressure

is sent to inlet (1). This pilot system pressure moves spool (2) to stop the main system

pressure from going to pilot valve (11). At the same time, the movement by spool (2)opens a passage for main system pressure to go to pilot valve (14). Added shims (13)

cause pilot valve (14) for the 225D to open at 31 700 kPa (4600 psi) and for 231D toopen at 33 100 kPa (4800 psi).

When a track motor is activated, oil pressure in passages (8) and (10) is limited to 31 700

kPa (4600 psi) for the 225D and 33 100 kPa (4800 psi) for the 231D. At any other time

the pressure is limited to 29 650 kPa (4300 psi).

When blocker valve (3) is installed in a reverse position in the valve bore, it will stop

main relief valve (4) from working. Reverse installation of the blocker valve makes it

possible to check the relief pressure settings of the line relief valves that protect the

cylinders and motors from outside forces.

Hydraulic Tank Air Pressure System

NOTICE

Damage can occur to the bent-axis piston pumps if the machine is

operated without an air pressure of 49 ± 14 kPa (7 ± 2 psi) in the

hydraulic tank. To prevent damage to pumps, it is very important that

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the yellow tank pressure warning lamp be OFF before the governor

control lever is pulled back into the high idle position.

Turbocharger Intake Manifold (Typical Example)

(1) Tap.

To prevent cavitation in the bent-axis pumps, a tap (1) off the engine turbocharger intakemanifold provides sufficient pressure to maintain 49 ± 14 kPa (7 ± 2 psi) in the hydraulic

tank.

Hydraulic Tank Breaker/Relief Valve

Hydraulic Tank

(2) Breaker/relief valve.

Mounted to the top of the hydraulic tank is breaker/relief valve (2). This valve allows thehydraulic tank to breathe, while keeping dust and debris out of the tank.

During normal machine operation, hydraulic oil will get hot and expand. As the oil

expands, it compresses the air at the top of the hydraulic tank. When air pressure reaches

138 ± 21 kPa (20 ± 3 psi), valve (2) will open and allow the air pressure to escape. The

breaker/relief valve maintains a specific air pressure in the tank once the hydraulic oil has

been brought up to operating temperature. This keeps all hydraulic lines full and helps to

prevent the hydraulic pumps from cavitating.

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When the machine has been shut down after running, the hot hydraulic oil will contract

(become smaller) as it cools. The cooling oil creates a vacuum in the hydraulic tank.Valve (2) opens at 0.0 ± 2 kPa (.00 ± .30 psi) vacuum and allows air into the hydraulic

tank. If a vacuum was maintained in the tank, the hydraulic oil would be held in the tank.This would allow the hydraulic pumps to cavitate when the machine was started.

Implement System Filter


(1) Filter housing. (2) Filter elements (two). (3) Valve. (4) Spring. (5) Cover. (6) Inlet passage. (7) Outlet

passage. (8) Chamber. (9) Spring. (10) Strainer.

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The filter for the implement system oil is installed horizontally along the right side of the

engine. Remove cover (5) to change two elements (2) and to clean and flush housing (1).

All the flow of return oil from the two bent-axis piston (variable displacement) pumps

goes into the filter at inlet passage (6). Unless filter elements (2) become stopped up (or when the oil is cold), all the oil goes through the elements and out through passage outlet(7).

Filter Location (Typical Example)

(1) Filter housing. (5) Cover. (11) Pressure switch.

When part of the flow of oil through the elements is stopped, there is an increase in oil

pressure in chamber (8) that opens valve (3). Valve (3) opens at 148 kPa (21.5 psi). Oilflow goes through valve (3) to passage (7) without going through the elements. All oil

flow goes through strainer (10) when valve (3) is open. The strainer will remove only

larger particles from the oil.

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A pressure switch (normally closed) is installed in the inlet passage. When the inlet

pressure comes close to the pressure that will open valve (3), the switch opens and theindicator in the cab (operator's compartment) gives a warning to change the filter

elements. If the indicator shows red after the oil is at operating temperature, inspect theelements for the cause of early restriction.

Return oil flow is from outlet passage (7) to the cooler bypass valve. When the oil

temperature is low, resistance to flow is high and causes an increase in oil pressure. This

causes the cooler bypass valve to open and most of the oil flow is through the valve (little

oil goes through the cooler). An increase in oil temperature causes less resistance of flow.

The valve opening becomes smaller and there is more oil flow through the cooler. The oil

flow from the cooler and the flow from the bypass valve goes back to the tank.

Filters (Pilot System And Case Drain)

Pilot System Filter (1) Filter. (2) Hydraulic tank.

Case Drain Filter (Viewed from left side)

(3) Filter.

Pilot system filter (1) is installed to the right of the bent-axis piston pumps. The input line

to the filter comes from the pilot system pump. The output line goes to the valve for pilot

system pressure. The bypass valve for the pilot system filter opens at 183 kPa (26.6 psi).

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Case drain filter (3) is installed on the support bracket for the front lines. The inlet line to

the filter comes from the pumps and motors. The outlet line goes to the tank. The bypassvalve for the case drain filter opens at 93 kPa (13.5 psi).

Pilot System Relief Valve

Pilot Relief Valve (Located Next To Hydraulic Tank)

The relief valve in the pilot system keeps the oil pressure at 2300 ± 170 kPa (335 ± 25

psi). Since the flow of oil in the pilot system is so small, most of the output from the

pump goes through the relief valve. The only oil needed by the system is the amount used

to shift one or more of the spools in the main control valves. As a result, the system

pressure is held constant at 2300 ± 170 kPa (335 ± 25 psi) except for short periods whena main valve spool is activated.

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Cross Section Of Relief Valve

(1) Chamber. (2) Spring. (3) Piston. (4) Spring. (5) Relief valve. (6) Adjusting screw. (7) Valve. (8) Inlet.

(9) Outlet.

Pilot Relief Valve

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Pilot system oil goes in the valve at inlet (8), through an orifice in valve (7) and fills

chamber (1) around spring (2). When the pressure in chamber (1) becomes higher thanthe force of spring (4), valve (3) opens and the oil in chamber (1) goes through valve (3)

and through outlet (9) to tank. The decrease in pressure in chamber (1) lets valve (7)move against the force of spring (2) and opens a passage for oil flow from inlet (8) to

outlet (9).

Outlet (9) is connected to tank. The force of spring (2) and the oil pressure in chamber (1)

controls the movement of valve (7). This action limits the amount of oil returned directly

to tank and keeps the system pressure constant.

Hydraulic And Directional Lock Valve

When the hand control lever for the hydraulic and directional lock valve is in OPERATE position (2), control lever (1) extends into the door of the cab. This helps the operator to

remember to move the lever to the LOCK position before he gets out of the cab.

Linkage (4) connects control lever (1) with spool (8) in valve (3). An outside oil line

connects the pilot oil to inlet (9). Another oil line connects outlet (6) to the pilot valves.When spool (8) is in the OPERATE position, oil flow from the pilot system goes through

the valve from inlet (9) to outlet (6) and then to the pilot valves. All of the components on

the machine can operate now.

Control Lever For Valve (3)

(1) Control lever (LOCK position).

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Control Lever For Valve (3)

(2) OPERATE position.

Bottom Floor Plate

(3) Hydraulic and directional lock valve. (4) Linkage to lock valve.


(3) Hydraulic and directional lock valve. (5) Detents (two). (6) Outlet to pilot valves. (7) Passage drilled in

spool. (8) Spool. (9) Inlet from the pilot system. (10) Outlet to tank.

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Schematic For Boom, Bucket And Stick

Control

NOTE: For Description Of Components Also See Pump Flow And Pressure Control

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Schematic For 225D And 231D (Earlier Style Shown)

(1) Cylinder, bucket.

(2) Oil line for main system oil from control valve for bucket to head end of bucket cylinder, bucket

CLOSE.

(3) Oil l ine for main system oil from control valve for bucket to rod end of bucket cylinder, bucket OPEN.

(4) Combination Line Relief And Makeup valves (five - 225D/231D, four 229D).

(5) Makeup Valves (one - 225D/231D, two - 229D).

(6) Oil line for main system oil from the control valve for boom to the head ends of the boom cylinders,

boom RAISE.

(7) Boom Check And Relief Valve (See Boom LOWER Control for operation).

(8) Cylinders, boom.

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(9) Oil line for main system oil from the control valve for boom to the rod ends of the boom cylinders,

boom LOWER.

(10) Boom Vent Valve (See Boom LOWER Control for operation).

(11) Oil line for main system oil from control valve for stick to rod end of stick cylinder, stick OUT.

(12) Stick Vent Valve (See Stick IN Control for operation).

(13) Stick Check And Relief Valve (See Stick IN Control for operation).

(14) Cylinder, stick.

(15) Oil line for main system oil from control valve for stick to head end of stick cylinder, stick IN.

(16) Swing/Stick Check Valve. This valve makes it possible to use the stick and swing or stick and lefttrack circuits at the same time.

(17) Main Control Valve For Right Track. This valve is controlled by the pilot valve for right track movement. It controls the flow of oil from the front pump to the right track motor.

(18) Main Control Valve For Bucket. This valve is controlled by the pilot valve for bucket. It controls the

flow of oil from the front pump to the bucket cylinder.

(19) Main Control Valve For Boom. This valve is controlled by the pilot valve for boom movement. It

controls the flow of oil from the front pump to the boom cylinders.

(20) Oil line for pilot pressure oil to boom crossover valve.

(21) Oil line for main system oil from boom crossover valve to the main control valve for boom.

(22) Crossover Valve For Boom And Stick Operation. This valve is controlled by the pilot valves for boom

and stick movement. They control the flow of oil from the front pump (stick crossover) and rear pump

(boom crossover). When they are activated, the flow from one pump combines (goes together) with the

flow from the other and boom and/or stick speed of operation is increased.

(23) Main Control Valve For Stick. This valve is controlled by the pilot valve for stick movement. It

controls the flow of oil from the rear pump to the stick cylinder.

(24) Main Control Valve For Left Track. This valve is controlled by the pilot valve for left track

movement. It controls the flow of oil from the rear pump to the left track motor.

(25) Main Control Valve For Swing. This valve is controlled by the pilot valve for swing movement. It

controls the flow of oil from the rear pump to the swing motor.

(26) Oil line for pilot pressure oil to main control valve for bucket OPEN.

(27) Oil line for pilot pressure oil to main control valve for bucket CLOSE.

(28) Oil line for pilot pressure oil to main control valve for boom LOWER.

(29) Oil line for pilot pressure oil to main control valve for boom RAISE.

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(30) Oil line for main system oil from the main control valve for right track to the blocker valve.

(31) Blocker Valve. This valve is controlled by pilot pressure oil from the shuttle valve. It controls the flow

of main system oil and pressure from the main control valve for right track (front pump) to the main controlvalve for left track.

(32) Oil line for pilot pressure oil to main control valve for stick IN.

(33) Oil line for pilot pressure oil to main control valve for stick OUT.

(34) Pilot Valve. Manually operated for control of pilot pressure oil to the main control valves for the boom

and bucket.

(35) Shuttle Valve. Allows pilot oil to stick crossover valve for stick IN and OUT.

(36) Pilot Valve. Manually operated for control of pilot pressure oil to the main control valves for the stick and swing.

(37) Oil Line for supply of pilot pressure oil to pilot control valves.

(38) Oil line for main system oil from the combiner valve (front pump) to the main control valves for right

track, bucket, boom and stick crossover.

(39) Oil line for main system oil from the combiner valve (rear pump) to the main control valves for swing,

left track, stick and boom crossover.



activated, the stick cylinder.

(41) Bent-axis Piston Pump (Rear). This is a variable displacement pump. It supplies the main oil flow to



(42) Combiner Valve For Main System Oil. This valve has internal passages that go to the relief valve for

main system pressure and, at the same time, it does not allow the flow of oil from the axial piston pumps to

combine (go together) except when the pressure on both pumps reaches relief valve pressure.

(43) Relief Valve For Main System Pressure. This valve limits the pressure of the main system oil to 29

650 kPa (4300 psi). When the pilot valve for machine travel is activated, this valve limits the system

pressure to 31 700 kPa (4600 psi) for the 225D and 33 100 kPa (4800 psi) for the 231D. System pressurefor machine travel on the 229D is limited to 29 650 kPa (4300 psi) and.

Boom, Bucket And Stick Control

Introduction

The boom, stick and bucket implements are operated by the pressure and flow from the

main system. Each of these implements is activated by sending oil to their respective

cylinders. The boom cylinders and bucket cylinder get their oil from the front pump. The

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stick cylinder gets its oil from the rear pump. Oil flow to the head ends of the boom

cylinders causes the boom to RAISE. Oil flow to the rod end of the stick cylinder causesthe stick to go OUT. Oil flow to the rod end of the bucket cylinder causes the bucket to

OPEN.

Modulation of the oil flow to the implements from either or both pumps is controlled bythe pilot oil through the manually operated pilot control valves.

System Oil Flow

Controls (Earlier Style Shown)(44) Control lever for spools in the pilot control valve for stick and swing functions. (45) Control lever for

spools in the pilot control valve for boom and bucket functions.

NOTE: Boom RAISE is used for an explanation of oil flow.

A constant maximum pressure is held at the inlets of the closed center pilot control

valves. By controlling pilot pressure through these valves the movement of the stems in

main control valves for boom ,bucket, stick, and swing. The stems in the main valves can

be moved to let any part or all of the main system oil go to an implement.

Levers (44) and (45) control the spool movement in the pilot control valves. Forward

movement of lever (44) causes the stem in pilot control valve (36) to move. This allows

pilot pressure to go through oil line (33) to main control valve (23). Stick control valve

(23) controls the main system pressure to stick cylinder (14). The pilot pressure at valve

(36) moves the spool and opens a passage for main system oil to go to the rod end of

cylinder (14). As the rod retracts, the end of the stick moves OUT. Movement of lever (44) back will move the end of the stick towards the machine (stick IN). Side-to-sidemovement of lever (44) controls the left and right swing movement of the upper

structure.

Forward movement of lever (45) lowers the boom assembly and movement of the lever

back raises the boom assembly. Side-to-side movement of the lever controls the

OPEN/CLOSE operation of the bucket.

Oil from the front pump (40) goes from combiner valve (42) through line (38) to the inlet

on right track valve (17). When the spools in valves (17), (18), and (19) are in the

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(19). All of the oil goes to the right track motor. (See Speed And Direction Control for

explanation of valve operation).

The implements (bucket and boom) controlled by valves (18) and (19) respectively, can

not be activated.

If the spool of valve (17) is moved part of its travel distance, only part of the oil flow in

line (38) goes to the track motor. The remainder of the oil flow goes through valves (18)

and (19) to the valve (22) and on to tank. If the spool in valve (18) or (19) is moved when

the spool in valve (17) is moved part way, the implement controlled by that valve will

operate but the rate of operation will be slower than normal.

When the spool in control valve (19) is moved to NEUTRAL, the oil flow in lines (6) and

(9) is stopped. If an outside force is put on the boom that pushes the boom down, boom

check and relief valve (7) opens when the pressure becomes 38 000 ± 700 kPa (5500 ±100 psi) for the 225D and 231D and 34 500 ± 700 kPa (5000 ± 100 psi) for the 229D.

When an outside force causes the boom cylinders to extend, oil is pushed through

combination line relief valve and makeup valve (4), then back to tank.

When the pressure in the head ends of the boom cylinders (line 6) becomes lower than

the pressure in the oil return passage, makeup valve (5) will open and oil from the return

oil passage goes to the head ends (line 6).

Combination Line Relief And Makeup Valves

Before doing any test on the line relief valves, refer to the Testing And

Adjusting section. Extreme caution must be used when testing the line

relief valves. These valves are set to open at 34 500 ± 700 kPa (5000 ±

100 psi), 35 850 ± 700 kPa (5200 ± 100 psi) and 38 000 ± 700 kPa (5500 ±

100 psi).

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Combination Line Relief And Makeup Valve

(1) Housing. (2) Spring. (3) Passage. (4) Valve assembly. (5) Spring. (6) Valve. (7) Chamber. (8) Chamber.

(9) Shims. (10) Passage. (11) Pilot valve. (12) Seat.

The pressure in any line between the control valve and its cylinder or motor is controlled by a line relief valve when the spool of the control valve is in NEUTRAL. The operation

of all of the line relief valves is basically the same. Left and right track valves, bucket

valves the rod end of the boom valve and both ends stick valve on the 225D and the head

end of the stick valve on the 229D and 231D have line relief valves that also act as

makeup valves.

On 225D and 231D machines equipped with increased pressure, only the line to the head

end of the stick cylinder will have a combination line relief and makeup valve. The line

relief valves for the head ends of the boom cylinders and for the stick cylinder on the

229D and on 225D and 231D with increased pressure are installed in separate valves.

(See Boom LOWER and Stick IN Control sections in this module for an explanation of

valve operation).

The line relief valve for the swing control valve is installed in the lines between the maincontrol valve and the swing motor. (See Swing Control section in this module for an

explanation of swing relief valve operation).

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The line relief valves for the LEFT and RIGHT track valves have shim adjustments to

open at 38 000 ± 700 kPa (5500 ± 100 psi) for the 225D, 229D and 231D.

The line relief valves for boom LOWER (line to rod end of cylinders), bucket OPEN and

CLOSE, and stick IN and OUT (both ends for the 225D, 229D and head end for the

231D) have shim adjustments to open at 34 500 ± 700 kPa (5000 ± 100 psi) for 225D and229D and 35 850 ± 700 kPa (5200 ± 100 psi) for 231D.

The line relief valves for boom RAISE (line to head end of cylinders) have shim

adjustments to open at 34 500 ± 700 kPa (5000 ± 100 psi) for the 229D and 38 000 ± 700

kPa (5500 ± 100 psi) for the 225D and 231D.

The line relief valve for stick OUT (for the 225D and 231D equipped with increase

pressure attachment) has shim adjustments to open at 38 000 ± 700 kPa (5500 ± 100 psi).

Spring (2) holds valve (4) and valve seat (12) against valve (6). The oil from chamber (8)

goes in the holes in valve (6) and fills the area around the base of valve (4). Oil can not

get to chamber (7) as long as valve (4) is on its seat.

The oil goes through passage (10) and fills the chamber in housing (1). When the spool in

the control valve is moved to the NEUTRAL position, oil flow through the lines to the

cylinder or motor is stopped. If an outside force causes the pressure to become high

enough to open pilot valve (11), oil in the chamber of spring (2) goes through passage (3)

and out the end of valve (4) into chamber (7) which is connected to a return line to tank.

The decrease in pressure in the chamber of spring (2), when valve (11) opens, lets valve

(4) move against the force of spring (2) and moves from its seat in valve (4). Oil from theline under pressure, goes in the small holes in valve (6) and out through chamber (7) to

tank. (See Makeup Valves for description of operation of makeup valve part of

combination line relief and makeup valves).

Makeup Valves

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Schematic For Boom Circuit (Earlier Style Shown)

(1) Line to rod ends of boom cylinders. (2) Passage. (3) Line relief valve. (4) Makeup valve. (5) Return oil passage. (6) Makeup valve. (7) Line to head ends of boom cylinders.

There are two kinds of makeup valves used. One type is a makeup valve by itself and the

other type is part of a line relief valve. The operation of both types of makeup valves is

the same. The following explanation will use boom LOWER as an example.

An oil line connects oil passage (1) to the rod ends of the boom cylinders. An inside

passage (2) connects line (1) with line relief valve (3) and makeup valve (4). Both valves

are one component (combination line relief and makeup valve) and are connected to

return oil passage (5).

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When the boom cylinders are forced to move faster than the pump can supply oil, there

will be a vacuum created in supply line (1). The oil flow that returns from the cylindersgoes through passage (7) and then to tank passage (5). The vacuum in line (1) lets the

pressure in tank passage (5) open makeup valve (4) against the force of its return spring.The oil in the tank passage then goes through line (2) and into line (1) that has the

vacuum. This provides a constant supply of oil to the boom cylinders.

The second type of makeup valve (6) does not have a line relief valve. The principle of

operation is the same as line relief valve (3) and makeup (4) valve combination. A

pressure difference across the valve will allow it to open and let oil go to the side with a

vacuum.

Load Check Valves

Load Check Valve (Typical Illustration)

(2) Load check valve.

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Main Control Valve For Bucket

(1) Return oil passage. (2) Load check valve. (3) Line to head end of bucket cylinder. (4) Line to rod end of

bucket cylinder. (5) Main control valve for bucket. (6) Oil supply passage.

Each control valve has a load check valve (2). The following explanation will use the

main control valve for bucket.

When the spool of control valve (5) is in NEUTRAL position, oil goes through the valve

from its inlet through passage (6) to the next valve (or tank). Movement of the spool, ineither direction, stops the flow of oil through passage (6). Oil pressure opens check valve

(2) and oil flows through the control valve to either passage (3) or (4). If the spool

movement connects passage (6) to (3), oil flow to passage (4) from passage (6) is not

possible, but passage (4) is connected to tank passage (1). If pump pressure in passage (6)

is less (or becomes less) than the cylinder oil pressure in passage (3), check valve (2) will

close to prevent reverse oil flow through passage (3).

Pilot Control Valves

The pressure of the pilot oil in lines (2) and (4) is held at approximately 2300 kPa (335 psi) by the action of the relief valve for pilot pressure. (See Pump Flow And Pressure

Control). Pilot pressure of 2300 kPa (335 psi) will move any spool in a main control

valve to its full travel. This lets maximum oil flow from the main system pumps go to acylinder or motor. The rate of main system oil flow through any main control valve is

controlled by a change in the pressure of the pilot oil that is used to activate the valve.

Pilot Control Valve (Stick And Swing)

(1) Pilot control valve (left side). (2) Line (pilot oil supply) (not shown).

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Pilot Control Valve (Boom And Bucket)

(3) Pilot control valve (right side). (4) Line (pilot oil supply).

Operator's Seat And Controls

(1) Pilot control valve for swing and stick. (3) Pilot control valve for boom and bucket.

To give the operator the ability to control this flow and pressure, two pilot control valves

are installed in the pilot system. Valve (1) is in the left arm rest and controls the stick in

and out movement and the right or left movement of the swing circuit. Valve (3) isinstalled in the right arm rest and controls the raise and lower movement of the boom and

the open and close movement of the bucket.

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Bottom Of Pilot Control Valve

(5) Outlet for boom RAISE or stick OUT. (6) Outlet for swing LEFT or bucket OPEN. (7) Outlet stick IN

or boom LOWER. (8) Inlet for pilot pressure and flow. (9) Outlet for return pilot pressure and flow. (10)

Outlet for swing RIGHT or bucket CLOSE.

The pilot valves are manually operated and send pilot oil to the end of the spool in the

main control valve selected for operation.

There are four pressure reducing type valve assemblies in each pilot valve. Two valve

assemblies are needed to operate each of the four implements.

When a control lever is moved, a plunger is pushed down in the pilot valve. Movement of the plunger causes a valve stem to move down and open a passage for pilot oil to go toone end of a main control valve spool. The pressure oil at the end of the main control

valve spool moves it until a passage is opened for main supply oil to the implement,

cylinder or motor.

The two pilot valves are the same. Three of the four valve assemblies in each valve are

the same. The fourth valve, which is used for stick IN and boom LOWER, uses a

different plunger. Identification of the ports is stamped on the bottom of the valve.

Boom Operation - Hold

When the control levers are in HOLD position, all of the plungers are in the same

position. Pilot oil from the pilot pump goes into the valve through inlet (8) to chamber (28) and is stopped by the position of stems (17) and (18). Passages (26) and (27) are

open to tank through chamber (25) and outlet (9).

Spring (23) pushes up on retainer (19) and plunger (12). Spring (23) holds stem (17)

down against retainer (19). Spring (22) pushes up on retainer (16) and plunger (15).

Spring (24) holds stem (18) down against retainer (20). There are spacers between theretainers and plungers that are used to change the force of springs (21) and (22).

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Pilot Control Valve

(5) Outlet. (7) Outlet. (11) Actuator plate. (12) Plungers (valve 1, 3 & 4). (13) Retainer. (14) Retainer. (15)

Plunger (valve 2). (16) Retainer. (17) Stem. (18) Stem. (19) Retainer. (20) Retainer. (21) Spring (inner).(22) Spring (inner). (23) Spring (outer). (24) Spring (outer). (25) Chamber. (26) Passage. (27) Passage. (28)

Chamber.

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Pilot Control Valve

Boom Raise

When the control lever is moved to the boom RAISE position, actuator plate (11) tilts to

the right. Actuator plate (11) pushes down on plunger (12) against the force of spring(23). Boom RAISE stem (17) moves down with plunger (12). The oil from pump inlet (8)

now can go through passage (27) from chamber (28) and out passage (5) to the raise end

of the main control valve for boom. The pressure of this oil on the end of the boom valve

spool causes it to move into the RAISE position.

The oil from the chamber at the opposite end of the main control valve spool for boom

comes back through outlet (7), through passage (26) in stem (18) and then into chamber

(25) and back to tank.

Oil pressure in outlet (5) pushes up against stem (17) and spring (21). Any increase in pressure in outlet (5) will push harder against stem (17) and spring (21). As stem (17)moves up, passage (27) is closed and the flow of oil is stopped to outlet (5) [the pressure

remains in outlet (5)]. At this point, stem (17) has moved off retainer (19) and is being

held in a pressure modulating position. The stem has established a balance between the

pressure in outlet (5) and the force of spring (21).

When the control lever has moved approximately 85% of the distance for full boom

RAISE, plunger (12) makes direct contact with the top of stem (17). When this happens,stem (17) is pushed down until passage (27) is again open to pilot pressure. Full pilot

pressure now goes to outlet (5).

When the boom control lever is released, spring (23) pushes up on plunger (12). Actuator

plate (11) returns the lever to HOLD position. Stem (17) moves up because retainer (19)has moved up with plunger (12) and the force of spring (21) is less. The oil in outlet (5)

can flow through passage (27) and chamber (25) to tank.

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Boom Lower

Boom LOWER stem (18) operates in a similar manner to the boom RAISE stem (17).

The difference is in plunger (15) that will never make direct contact with stem (18). As aresult, full pilot pressure of 2300 kPa (335 psi) will never be supplied to outlet (7).

Stick In

Since the pilot valves are identical, the operation of stem (18) will be the same as boom

LOWER.

Stick Out, Bucket Open Or Close And Swing Right Or Left

Operation of the pilot valve for these functions is the same as that described for boomRAISE.

Pilot Control Valve (Stick And Swing)

(1) Pilot control valve for stick and swing. (2) Oil line to pilot oil inlet. (29) Outlet line to tank. (30) Pilot

oil line for stick OUT. (31) Pilot oil line for swing RIGHT. (32) Pilot oil line for swing LEFT. (33) Pilot oil

line for stick IN.

Pilot Control Valve (Boom And Bucket)

(3) Pilot control valve for boom and bucket. (4) Inlet for pilot oil. (34) Pilot oil line for boom RAISE. (35)

Outlet line to tank (not shown). (36) Pilot oil line for bucket OPEN. (37) Pilot oil line for boom LOWER.

(38) Pilot oil line for bucket CLOSE.

Boom, Bucket And Stick Cylinders

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When oil flow from the control valve goes in passage (2) to the rod end of the cylinder,

oil in the head end is pushed out through passage (1). When nut (3) and stop (4) go in thesmaller bore at the end of cylinder (6), the area of the outlet passage becomes smaller.

The oil, moved by piston (5), going through a smaller outlet, must move at a lower rate.This gives a reduction to the rate of rod travel. This design gives a cushion effect at the

end of piston rod travel. Stop (7) works in a similar way for travel in the direction of the

rod end.

Bucket, Boom And Stick Cylinders (Typical Example)

(1) Oil passage, connected to main control valve. (2) Oil passage, connected to main control valve. (3) Bolt.

(4) Stop. (5) Piston. (6) Cylinder. (7) Stop. (8) Piston rod.

NOTE: The boom and bucket cylinders have stops on the rod end only (boom RAISE,

bucket CLOSE). The stick cylinder has stops on both ends.

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Cylinder Stops (Snubbers)

Figure 1. Nut and stop (snubber) about to go into small bore in head of cylinder. Figure 2. Stop begins to

reduce the flow of oil out of the head. The oil in the head makes a cushion for the shock loads and slows

down the rod movement. Figure 3. The cylinder has fully bottomed out.

Crossover Circuit Operation

Valves In NEUTRAL

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Schematic Of Crossover Circuits (All valves are shown in NEUTRAL position)

(1) Line [main system oil from the combiner valve (front pump) to the main control valves for right track, bucket, boom and stick crossover]. (2) Overspeed valve (right track REVERSE). (3) Spool (right track

control valve). (4) Spool (bucket control valve). (5) Spool (boom control valve). (6) Line [from boom

crossover valve to main control valve for boom (5)]. (7) Spool (boom and stick crossover valve). (8) Spool(stick control valve). (9) Spool (left track control valve). (10) Overspeed valve (left track FORWARD).

(11) Spool (swing control valve). (12) Line [main system oil from the combiner valve (rear pump) to the

main control valves for swing, left track, boom and stick crossover]. (13) Overspeed valve (right track

FORWARD). (14) Pilot control valve (boom and bucket circuits). (15) Line [pilot pressure oil from pilot

control valve for boom to main control valve for boom RAISE and oil line (17)]. (16) Line [pilot pressure

oil from pilot control valve for boom to main control valve for boom LOWER]. (17) Line [pilot pressure oil

from line (15) to crossover valve for boom]. (18) Line [pilot pressure oil from shuttle valve (28) to blocker

valve (26)]. (19) Line [pilot pressure oil from line (30) to shuttle valve (20)]. (20) Shuttle valve. (21) Line

[pilot pressure oil from shuttle valve (20) to crossover valve for stick]. (22) Line [oil from pilot control

valve for stick to shuttle valve (20) and main control valve for stick OUT]. (23) Overspeed valve (left track

REVERSE). (24) Line [pilot pressure oil from pilot control valve for swing to main control valve for swing

RIGHT and line (29)]. (25) Line [pilot pressure oil from pilot control valve for swing to main control valve

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for swing LEFT and line (27). (26) Blocker valve. (27) Line [pilot pressure oil from line (25) to shuttle

valve (28)]. (28) Shuttle valve. (29) Line [pilot pressure oil from line (24) to shuttle valve (28)]. (30) Line

[from pilot control valve for stick to main control valve for stick IN and oil line (19)]. (31) Pilot control

valve (stick and swing circuits).

This schematic shows the normal flow of oil from the bent-axis piston pumps (lines 1 and

12) when all of the spools in the main control valve are in NEUTRAL.

Boom RAISE Position

Schematic Of Boom Crossover Circuit (Boom valve and boom crossover valve in boom RAISE position)

(1) Line [main system oil from the combiner valve (front pump) to the main control valves for right track,

bucket, boom and stick crossover]. (5) Spool [boom control valve]. (7) Spool [boom and stick crossover

valve]. (12) Line [main system oil from the combiner valve (rear pump) to the main control valves for

swing, left track, stick, and boom crossover]. (14) Pilot control valve (boom and bucket circuits). (15) Line

[pilot pressure oil from pilot control valve for boom to main control valve for boom RAISE and line (17)].

(17) Line [pilot pressure oil from line (15) to crossover valve for boom]. (32) Passage [to rod ends of

cylinders for boom LOWER. (In this illustration, return oil from the rod ends of the boom cylinders returns

to tank through this passage when the spool is in the boom RAISE position)]. (33) Passage (to head ends of

cylinders for boom RAISE). (34) Load check valve (boom circuit).

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This schematic shows the oil flow from the bent-axis piston pumps (lines 1 and 12) when

the lever for pilot valve (14) is pulled back for boom RAISE.

Spool (5), which is the main control valve for boom movement begins to move at

approximately 415 kPa (60 psi) pilot pressure. When the pilot pressure reaches 830 kPa

(120 psi) boom and stick crossover spool (7) begins to move. Both valves will be fullyopen when the pilot pressure reaches 1720 kPa (250 psi).

Stick IN And Swing RIGHT

Schematic Of Stick Crossover Circuit (Swing RIGHT; Stick valve and stick crossover valve in stick IN

position)

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(1) Line [main system oil from the combiner valve (front pump) to the main control valve for right track,

bucket, boom and stick crossover]. (7) Spool [boom and stick crossover valve]. (8) Spool (stick control

valve). (11) Spool (swing control valve). (12) Line [m ain system oil from the combiner valve (rear pump)

to the main control valves for swing, left t rack, stick and boom crossover]. (18) Line [pilot pressure oilfrom shuttle valve (28) to blocker valve (26)]. (19) Line [pilot pressure oil from line (30) to shuttle valve

(20)]. (20) Shuttle valve. (21) Line [pilot pressure oil from shuttle valve (20) to crossover valve for stick].

(24) Line [pilot pressure oil from pilot control valve for swing to main control valve for swing RIGHT and

line (29)]. (26) Blocker valve. (28) Shuttle valve. (29) Line [pilot pressure oil from line (24) to shuttle valve

(28)]. (30) Line [from pilot control valve for stick to main control valve for stick IN and oil line (19)]. (31)Pilot control valve (stick and swing circuits). (35) Passage [to rod end of cylinder for stick IN. (36) Passage

[to swing motor for swing LEFT. (37) Passage [to head end of cylinder for stick OUT. (38) Passage (to

swing motor for swing RIGHT).

This schematic shows the oil from the bent-axis piston pumps (lines 1 and 12) when the

control lever for pilot valve (31) is moved to the swing RIGHT and stick IN position.

Pilot oil in line (24) at a pressure of approximately 550 kPa (80 psi) will begin to move

spool (11) for swing RIGHT. At approximately 1720 kPa (250 psi), spool (11) will becompletely open, stopping the flow of rear pump oil from the rest of the spools in the five

stem control valve. The pilot oil in line (24) has also gone through line (29) to shuttlevalve (28).

NOTE: Shuttle valve (28) directs pilot oil pressure through line (18) and causes the spool

in blocker valve (26) to open. This will allow front pump oil to be used by both track

motors for movement of the machine when the swing valve is activated. Shuttle valve(28) is mounted to lower part of the bracket located behind the main control valve for

bucket.

If the control lever is moved to the stick IN or OUT position at this time, pilot oil will gothrough line (30) and at 415 kPa (60 psi) spool (8) will begin to open. At the same time,

pilot oil in line (19) will go through shuttle valve (20) and out through line (21) to boom

and stick crossover valve spool (7). At approximately 830 kPa (120 psi), spool (7) willstart to open and let front pump flow go to the head end of the stick cylinder for stick IN.

Stick Out And Swing Left

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Schematic Of Stick Crossover Circuit (Swing LEFT; Stick valve and stick crossover valve in stick OUT

position)(1) Line [main system oil from the combiner valve (front pump) to the main control valve for right track,


valve). (11) Spool (swing control valve). (12) Line [main system oil from the combiner valve (rear pump)

to the main control valves for swing, left t rack, stick and boom crossover]. (18) Line [pilot pressure oil

from shuttle valve (28) to blocker valve (26)]. (20) Shuttle valve. (21) Line [pilot pressure oil from shuttle

valve (20) to crossover valve for stick]. (22) Line [pilot pressure oil from pilot control valve for stick to

shuttle valve (20) and main control valve for stick OUT]. (25) Line [pilot pressure oil from pilot control

valve (31) for swing to main control valve for swing LEFT and oil line (27)]. (26) Blocker valve. (27) Line

[pilot pressure oil from oil line (25) to shuttle valve (28)]. (28) Shuttle valve. (31) Pilot control valve (stick

and swing circuits). (35) Passage [to rod end of cylinder for stick IN. (36) Passage [to swing motor for

swing LEFT. (37) Passage [to head end of cylinder for stick OUT. (38) Passage (to swing motor for swing

RIGHT).

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the control lever for pilot valve (31) is moved to the swing LEFT and stick OUT position.Pilot oil in line (25), at a pressure of approximately 550 kPa (80 psi) will begin to move

spool (11) for swing LEFT. At approximately 1720 kPa (250 psi), spool (11) will becompletely open, stopping the flow of rear pump oil from the rest of the spools in the four

stem control valve. The pilot oil in line (25) has also gone through line (27) to shuttle

valve (28).


in blocker valve (26) to open. This will allow front pump oil to be used by both track

motors for movement of the machine when the swing valve is activated.

If the control lever is moved to the stick OUT or IN position at this time, pilot oil will gothrough line (22) and at approximately 415 kPa (60 psi), spool (8) will begin to open. At

the same time, pilot oil in line (22) will go through shuttle valve (20) and out through line(21) to boom and stick crossover valve (7). At approximately 830 kPa (120 psi), spool (7)will start to open and let front pump flow go to the rod end of the stick cylinder for stick

out.

Stick Out

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Schematic Of Stick Crossover Circuit (Stick valve and stick crossover valve in stick OUT position)

(1) Line [main system oil from the combiner valve (front pump) to the main control valves for right track,


valve). (12) Line [main system oil from the combiner valve (rear pump) to the main control valves for swing, left track, stick and boom crossover]. (20) Shuttle valve. (21) Line [pilot pressure oil from shuttle

valve (20) to crossover valve for stick]. (22) Line [pilot pressure oil from pilot control valve for stick toshuttle valve (20) and main control valve for stick OUT]. (36) Passage (stick crossover valve). (31) Pilot

control valve (stick and swing circuits). (35) Passage [to rod end of cylinder for stick IN. (37) Passage [to

head end of cylinder for stick OUT.


only the stick valve is activated for stick OUT. At a pressure of approximately 415 kPa

(60 psi), pilot oil in line (22) will begin to move spool (8). At the same time, pilot oil in

line (22) will go through shuttle valve (20) and line (21) to stick crossover valve (7).When the pilot pressure reaches 830 kPa (120 psi), spool (7) will start to open. Front

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pump flow will combine with rear pump flow and give an increase in the rate of

movement by the stick.


in stick crossover valve to shift. This will allow front pump oil to joint rear pump oil for

two pump operation of stick IN or OUT. Shuttle valve (20) is mounted to upper part of the bracket located behind the main control valve for bucket.

Boom Lower Control

Introduction

Top View Of Front Main Control Valve

(1) Boom check and relief valve. (2) Boom vent valve (not shown).

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Schematic For Boom Circuit (Earlier Style Shown)

(1) Boom check and relief valve. (2) Boom vent valve. (3) Boom cylinders. (4) Oil line for main system oil,

boom LOWER. (5) Oil line to head ends of boom cylinders. (6) Check valve. (7) Oil line from boom check

and line relief valve to boom vent valve. (8) Oil line to tank. (9) Oil line for pilot pressure oil to boom vent

valve. (10) Oil line for pilot pressure oil, boom RAISE. (11) Main control valve for boom. (12) Oil line for

pilot pressure oil, boom LOWER. (13) Oil line for main system oil, boom RAISE. (14) Oil line to tank.

(15) Relief valve.

Some applications of an excavator need careful and exact control of boom movement.

The operator must be able to control boom LOWER to give a small, slow movements.

During this operation, the boom must remain in a stationary position (except when

changed by activation of the boom valve). To do this, boom check valve (1) has beeninstalled in the line to the head ends of the boom cylinders. This check valve will keep

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the down drift of the boom assembly as near zero as possible. Boom vent valve (2)

provides a way to lower the boom when the engine is not running.

Boom Check And Relief Valve

Cross Section Of Boom Check And Relief Valve(1) Check and relief valve for boom LOWER. (6) Check valve. (14) Oil passage (tank). (15) Relief valve.

(16) Spring. (17) Shoulder. (18) Oil passage. (19) Oil passage. (20) Oil passage.

During boom RAISE, oil flow from line (13) goes in passage (18), opens check valve (6)and goes out passage (19). From passage (19), the oil goes through line (5) to the head

ends of boom cylinders (3).

When the spool in control valve (11) is moved to NEUTRAL, check valve (6) closes. The

weight of the boom assembly working on the head ends of the boom cylinders causes pressure in line (5), passage (19) and the chamber of spring (16). Oil pressure and the

force of spring (16) hold check valve (6) closed. If an external force on the boom

assembly causes an increase of oil pressure in line (5) and passage (19) of 38 000 kPa

(5500 psi) for the 225D and 231D and 34 500 kPa (5000 psi) for the 229D, relief valve

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(15) opens and oil goes out passage (14) to a return line to the tank. (See Combination

Line Relief And Makeup Valves in this module for operation of the relief valve). Maincontrol valve (11) does not have a line relief valve in the RAISE end of the valve. Valve

(15) in boom check and relief valve (1) is the line relief valve for boom RAISE.

During boom LOWER, oil flow of the main system puts pressure on the oil in the rodends of the boom cylinders through line (4). Return oil from the head ends of the boom

cylinders goes through line (5) to passage (19). When the lever for the pilot control valve

is moved to the LOWER position, pilot oil pressure in lines (9) and (12) shift the spool in

boom vent valve (2).

Line (7) and passage (20) from check valve (6) is now open to tank. This releases oil

pressure in the chamber of spring (16). Oil pressure on shoulder (17) of valve (6) movesvalve (6) against the force of spring (16). The oil in passage (19) goes out passage (18) to

main control valve (11) through line (13).

Boom Vent Valve

Cross Section Of Boom Vent Valve

(2) Boom vent valve. (21) Plunger. (22) Ball. (23) Inlet passage from check valve (12). (24) Inlet passage

for pilot oil. (25) Spool. (26) Oil passage. (27) Spring. (28) Oil passage.

When the pilot control valve is in the NEUTRAL position, there is no oil pressure in pilot

oil lines (9), (10) and (12). Spring (27) pushes spool (25) to the end of the valve bore.

Any external force that pushes down on the boom assembly puts pressure on the oil in theline from the head ends of the boom cylinders and passage (19). Check valve (6) is held

in place by the oil in line (7) which is stopped by ball (22) and spool (25). When the lever

for the pilot control valve is pushed toward the boom LOWER position, there is a

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pressure increase in pilot oil lines (9) and (12). Oil pressure in line (9) to passage (24)

moves spool (25) against the force of spring (27). Spool movement opens a way for oilflow from passage (23), by spool (25) through the chamber for spring (27), through

passage (26) to a return line to tank. Passage (23) also causes a release of oil pressure inthe chamber for spring (16). Check valve (6) opens for flow of return oil from the head

ends of boom cylinders (3) to valve (11) and to return line to tank.

If the boom assembly is in the RAISE position and the engine can not be started for

power down, use boom vent valve (2) to lower the boom. When there is no engine power

available, valve (11) will be in the NEUTRAL position to stop oil flow in lines (4) and

(13) (to the boom cylinders). There is no pilot pressure to move spool (25) for release of

the pressure that holds check valve (6) closed.

To lower the boom under these conditions, loosen plunger (21). This opens a way for oil

flow from line (7) through passage (23), past ball (22), through passage (28) to thechamber of spring (27) and on to tank. The boom will lower slowly.

NOTE: In situations where excess drift occurs, make sure plunger (21) is in far enough

to seat ball (22).

Stick IN Control


(1) Stick check and relief valve. (2) Stick vent valve (not shown). (13) Oil line for main system oil, stick

OUT.

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Schematic For Stick Circuit (Earlier Style Shown)

(1) Stick check and relief valve. (2) Stick vent valve. (3) Stick cylinder. (4) Oil line for main system oil,stick IN. (5) Oil line to rod end of the stick cylinder. (6) Check valve. (7) Oil line from stick check and line

relief valve to stick vent valve. (8) Oil line to tank. (9) Oil line for pilot pressure oil to stick vent valve. (10)

Oil line for pilot pressure oil, stick OUT. (11) Main control valve for stick. (12) Oil line for pilot pressure

oil, stick IN. (13) Oil line for main system oil, stick OUT. (14) Oil line to tank. (15) Relief valve.

To give more exact control during lifting of heavy loads, the stick must remain in a

stationary position (except when changed by activation of the main control valve for

stick). This is accomplished by the use of stick check and relief valve (1) and stick vent

valve (2) installed in the line to the rod end of the stick cylinder. This check valve will

keep the IN drift of the stick assembly as near zero as possible.

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Operation of stick OUT is identical to that explained in the section Boom Lower Control.

Relief Valve (11) opens at 34 500 kPa (5000 psi) for the 225D and 229D and 35 850 kPa(5200 psi) for the 231D.

Relief Valve (11) opens at 38 000 kPa (5500 psi) for the 225D and 231D with increased

pressure.

The stick check and relief valve and stick vent valve are standard on the 229D and are

part of the increased pressure attachment on the 225D and 231D.

Schematic For Speed And Direction

Control


Schematic For 225D and 231D (Earlier Style Shown)

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(1) Brake For Right Track. Brakes are spring engaged at all times except when a pilot valve for machine

travel is activated.

(2) Bent-Axis Piston Motor. Installed to give movement to the right track.

(3) Brake For Left Track. Brakes are spring engaged at all times except when a pilot valve for machine

travel is activated.

(4) Bent-Axis Piston Motor. Installed to give movement to the left track.

(5) Oil line for main system oil from main control valve to track motor for right track FORWARD.

(6) Combination Line Relief And Makeup valves.

(7) Oil line for main system oil from main control valve to track motor for right track REVERSE.

(8) Oil line for main system oil from main control valve to track motor for left track FORWARD.

(9) Oil line for main system oil from main control valve to track motor for left track REVERSE.

(10) Main Control Valve For Right Track. This valve is controlled by the pilot valve for right track

movement. It controls the flow of oil from the front pump to the right track motor.

(11) Oil line for main system oil from the main control valve for right track to the blocker valve.

(12) Blocker Valve. This valve lets oil from the right track (front pump) go to the left track whenever the

swing is activated while the machine is moving. The rate of track speed will be reduced when this happens.

(13) Oil line for main system oil from the blocker valve to the main control valve for the left track.

(14) Main Control Valve For Left Track. This valve is controlled by the pilot valve for left track

movement. It controls the flow of oil from the rear pump to the left track motor.

(15) Oil line for pilot pressure oil to main control valve for right track FORWARD.

(16) Oil line for pilot pressure oil to main control valve for right track REVERSE.

(17) Pilot Valve. Manually operated. Controls the direction of rotation of the right tracks.

(18) Pilot Valve. Manually operated. Controls the flow and pressure of pilot oil to the main control valvefor machine movement in the REVERSE direction.

(19) Pilot Valve. Manually operated. Controls the flow and pressure of pilot oil to the main control valve

for machine movement in the FORWARD direction.

(20) Pilot Valve. Manually operated. Controls the direction of rotation of the left tracks.

(21) Oil line for pilot pressure oil to main control valve for right track REVERSE.

(22) Oil line for pilot pressure oil to main control valve for right track FORWARD.

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(23) Oil line for pilot oil to blocker valve from the shuttle valve.

(24) Double check Valve. (Inside of speed control and steering valve).

(25) Oil line for pilot oil to track brake valve.

(26) Oil line for the supply of pilot system oil to the pilot valves for speed and direction control.

(27) Oil line for supply of pilot system oil to the pilot valves.

(28) Oil line for main system oil from the combiner valve (front pump) to the main control valves for right

track, bucket, boom and stick crossover.

(29) Oil line for main system oil from the combiner valve (rear pump) to the main control valves for swing,

left track, stick and boom crossover.

(30) Control Valve For Track Brakes. Pilot operated. When valve (18) or (19) is pushed down, sends pilot

system oil to disengage track brakes. Also sends pilot system oil through line (35) to main relief valve to

change opening pressure of relief valve (225D only).

(31) Oil line from the track brake valve to the track brakes.



activated, the stick cylinder.

(33) Bent-axis Piston Pump (Rear). This is a variable displacement pump. It supplies the main oil flow to



(34) Combiner Valve For Main System Oil. This valve has internal passages that go to the relief valve for

main system pressure and, at the same time, it does not allow the flow of oil from the axial piston pumps to

combine (go together) except when the pressure on both pumps reaches relief valve pressure.

(35) Oil line for pilot oil to the relief valve for main system.

(36) Main relief valve (part of the combiner valve).

Speed And Direction Control

Introduction

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Track Circuits

(1) Brake for right track. (2) Right track motor. (3) Brake for left track. (4) Left track motor. (5) Oil line for

main system oil, right track FORWARD. (7) Oil line for main system oil, right track REVERSE. (8) Oil

line for main system oil, left track FORWARD. (9) Oil line for main system oil, left track REVERSE. (10)

Main control valve for right track. (14) Main control valve for left track. (15) Oil line for pilot pressure oil,

right track FORWARD. (16) Oil line for pilot pressure oil, right track REVERSE. (21) Oil line for pilot

pressure oil, left track REVERSE. (22) Oil line for pilot pressure oil, left track FORWARD. (31) Oil line

from the track brake valve to the track brakes. (39) Oil lines for case drain from motors to filter for case

drain. (40) Swivel group.

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Left Track Motor (Typical Example)

(3) Brake for left track. (4) Motor for left track. (8) Oil line for main system oil from main control valve to

motor for left track FORWARD. (9) Oil line for main system oil from main control valve to motor for left

track REVERSE. (31) Oil line from the track brake valve to the track brakes. (39) Oil lines for case drain

from motors to filter for case drain.

The oil flow of the main system is used to turn two fixed displacement, bent-axis piston

motors (2) and (4). They move the machine in FORWARD and REVERSE directions and

turn the machine. Oil flow from the main control valves to the motors, through lines (5)

and (8), moves the machine in the FORWARD direction. Return oil from the motors goesthrough lines (7) and (9) when the machine moves in the FORWARD direction. Oil flow

from the control valves to the motors, through lines (7) and (9), moves the machine in the

REVERSE direction. Return oil from the motors goes through lines (5) and (8) when the

machine moves in the REVERSE direction.

Brakes (1) and (3) are engaged by springs. When the spool in pilot valve (18) or (19) is

pushed down, pilot oil flows through line (25), shifting the spool in track brake valve(30). This opens a path for pilot oil pressure to flow through line (31), causing the releaseof the brakes before the motors start to turn.

NOTE: When valve (18) and (19) cause release of the brakes, pilot oil is also sent

through line (35) to main relief valve (36). This causes the pressure in the relief valve for

the main system oil to be limited to 31 700 kPa (4600 psi) on the 225D and to 33 100 kPa

(4800 psi) on the 231D.

Push down on foot pedal (42) for machine movement in the REVERSE direction and on

foot pedal (46) for machine movement in the FORWARD direction. Move lever (44)

toward position (43) to turn the machine to the left and toward position (45) to turn themachine to the RIGHT.

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Oil pressure from the pilot system is needed for release of the track brake before the

machine can be moved. The functions of the track brake valve are:

1. To stop flow of pilot system oil to the track brakes so that the brakes will be

ON and keep the machine stationary when the travel pedal is not pushed down.

2. To send oil to the brakes for brake release at the start of machine movement.

3. To keep the machine stationary when there is a partial brake application caused

by a decrease of pressure in the pilot system oil.

Before the engine is started, springs (1) and (11) push spools (4) and (15) to the right.When the engine is started, the increase of pressure in the pilot system oil in oil passage

(12) is sent through passage (6) to chamber (5). Oil pressure in chamber (5) moves spool

(4) against the force of spring (1) to make a connection between oil passage (3) and oil passage (8). There is no flow in passage (3) until one of the speed and direction valves in

the pilot system is activated.

Activation of either of the speed and direction valves causes an increase in pressure in

passage (3). Oil pressure from the pilot system in chamber (5) has moved spool (4).

There is an increase of oil pressure in passage (8) and chamber (100). Oil pressure in

chamber (10) moves spool (15) against the force of spring (11) to make a connection

between oil passage (12) and (13). Supply oil from the pilot system at approximately2300 kPa (335 psi), goes into passage (12). An oil line connects passage (13) to the track

brakes. When passages (12) and (13) are connected, the oil pressure that causes release of

the track brakes, is the same as the pressure of the pilot system oil.

Oil pressure of approximately 205 kPa (30 psi) is enough to move spool (15) and let oilflow from passage (13) to the track brakes.

An oil pressure of approximately 1720 kPa (250 psi) in oil passage (13) is needed for complete release of the brakes. If there is a decrease of pressure in the pilot system oil to

less than 1720 kPa (250 psi), the brakes will be partially engaged. To stop operation with

partially engaged brakes, the force of spring (1) moves spool (4) when the pressure in

chamber (5) [connected to the pilot system through passage (6)] is less than 1720 kPa

(250 psi). Movement of spool (4) stops oil flow from oil passage (3) to chamber (10).

With a reduction of oil pressure in chamber (10), the force of spring (11) moves spool(15) to stop oil flow from oil passage (12) to oil passage (13). When there is no oil

pressure in passage (13), the track brakes are activated by its springs.

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Track Brake Valve

(1) Spring. (2) Valve. (3) Inlet passage (oil flow from pilot system valve). (4) Spool. (5) Oil chamber. (6)

Oil passage. (7) Plunger. (8) Oil passage. (9) Oil passage. (10) Oil chamber. (11) Spring. (12) Inlet passage(pilot system supply oil). (13) Outlet passage (oil to release brakes). (14) Outlet to tank. (15) Spool.

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Track Brake Valve

Track Brake Valve (located next to hydraulic tank)

(2) Valve. (3) Inlet (oil flow from pilot system valve). (7) Plunger. (12) Inlet passage (pilot system supply

oil). (13) Outlet passage (oil to release brakes). (14) Outlet to tank.

Speed Control And Steering Valve

View Of Speed Control And Steering Valve

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(1) Pilot valve. Controls the flow and pressure of pilot oil to the main control valves for machine movement

in the REVERSE direction. (3) Pilot oil line to the main control valve for left track REVERSE. (4) Pilot oil

line to the main control valve for left track FORWARD. (6) Pilot Valve. Controls the direction of rotation

of the tracks. (8) Pilot oil line to the main control valve for right track FORWARD. (9) Pilot oil line to themain control valve for right track REVERSE. (11) Pilot valve. Controls the flow and pressure of pilot oil to

the main control valves for machine movement in the FORWARD direction. (20) Oil line for pilot oil to the

track brake valve. (22) Oil line for supply of pilot system oil to the pilot valves for speed and direction.

Speed Control And Steering Valve

NOTE: The following description of valve operation is for machines NOT equipped withincreased pressure. The only difference in valve operation between machines equippedwith increased pressure and not equipped is how the signal oil to the track brake valve is

sent.

Forward Direction

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Cross Section Of Speed Control And Steering Valve (FORWARD Direction)

(1) Pilot valve [control of flow and pressure of pilot oil to the main control valves for machine movement

in the REVERSE direction]. (2) Spool in valve (1) [shown in NEUTRAL position]. (3) Oil line [pilot oil to

the main control valve for control of movement of left track in REVERSE]. (4) Oil line [pilot oil to the

main control valve for control of movement of left track in FORWARD]. (5) Spool in valve (6) for control

of direction of rotation of the left track (steering). (6) Pilot valve [control of the direction of rotation of the

tracks]. (7) Spool in valve (6) for control of direction of rotation of the right track (steering). (8) Oil line

[pilot oil to the main control valve for control of movement of right track in FORWARD direction]. (9) Oil

line [pilot oil to main control valve for control of movement of right track in REVERSE direction]. (10)Spool in valve (11) [shown in position for movement of the machine in FORWARD direction]. (11) Pilot

valve [control of flow and pressure of pilot oil to the main control valves for machine movement in the

FORWARD direction]. (12) Spring. (13) Oil chamber. (14) Oil passage. (15) Oil chamber [connected to

inlet (22)]. (16) Spool. (17) Oil chamber. (18) Spring. (19) Double check valve (not used on machines

equipped with increased pressure). (20) Oil line [to track brake valve]. (21) Oil chamber. (22) Inlet line

[supply of pilot oil to pilot valves (1), (6) and (11)]. (23) Oil chamber. (24) Oil chamber [connected to inlet

(22)]. (25) Oil chamber. (26) Oil passage.

When the foot pedal for FORWARD movement is pushed down, spool (10) movesagainst the force of spring (12). Spool (16) moves down to make a connection for pilot

pressure oil between chamber (15) and passage (14). Oil fills passage (14) and goes from

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passage (14) to oil chambers (13) and (25). Line (4) makes a connection for oil flow

between chamber (25) and the main control valve for left track. Line (8) makes aconnection for oil flow between chamber (13) and the main control valve for right track.

Pilot pressure oil in lines (4) and (8) shifts the spools in both track valves right, allowingflow of main system oil to the track motors. This moves both track motors in the

FORWARD direction. The machine moves FORWARD.

Oil pressure in passage (14) causes double check valve (19) to open for oil flow into line

(20). Line (20) is connected to the track brake valve. Oil pressure in line (20) to the track

brake valve causes the valve to send pilot pressure the oil to track brakes. On machines

with increased pressure, oil pressure in passage (14) is sent to the increased pressure

valve, which sends a signal to track brake valve (5). This pressure releases the brakes so

the machine can move. (See Track Brake Valve section for an explanation of valve

operation).

When there is an increase in oil pressure in passage (14), there is an increase in pressurein chamber (17) because drilled passages in spool (16) make a connection between

passage (14) and chamber (17). The pressure of the oil and the force of spring (18), in

chamber (17), moves spool (10) against the force of spring (12) to stop the flow of oil

from inlet (22) to passage (14) when the two forces are in balance.

In this way, the pressure of the oil in passage (14) is controlled by the amount of

compression of spring (12). When the compression of spring (12) is at its maximum, the

oil pressure in passage (14) is the same as the pressure of the pilot system oil.

Spring holds spools (2), (5), (7) and (10) in the NEUTRAL position. When these spoolsare in the NEUTRAL position, inlet (22) and chambers (15) and (24) are connected to the

pilot system oil and have a pressure of approximately 2300 kPa (335 psi). All other oil passages and chambers in pilot valves (1), (6) and (11) are open to tank pressure.

Right Pivot Turn

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Cross Section Of Speed Control And Steering Valve (RIGHT PIVOT Turn)

(1) Pilot valve (controls flow and pressure of pilot oil to the main control valves for machine movement in

the REVERSE direction). (2) Spool in valve (1). (4) Oil line for pilot oil to the left track main control valve

for FORWARD movement. (5) Spool in valve (6) (controls direction of left track-steering). (6) Pilot valve

(controls direction of rotation for left and right tracks). (7) Spool in valve (6) (controls direction of right

track-steering). (8) Oil line for pilot oil to the right track main control valve for FORWARD movement.

(10) Spool in valve (11). (11) Pilot valve (controls flow and pressure of pilot oil to the main control valves

for machine movement in the FORWARD direction). (13) Oil chamber. (14) Oil passage. (25) Oil

chamber. (26) Oil passage. (27) Spring (outer). (28) Spring (inner).

Spool (10) is pushed down for FORWARD movement of the machine. Partial movement

of the steering control lever to the right moves spool (7) down against the force of spring

(28). When the retainer on spring (28) makes contact with the retainer on spring (27),

spool (7) has stopped the flow of pilot oil between passage (14) and chamber (13). This

stops the flow of pilot oil through line (8) to the right track control valve. The spool in theright track valve moves to the NEUTRAL position. This stops the flow of main system

oil to the right track motor, which stops rotation of the right track.

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Pilot oil in passage (14) flows through chamber (25) and line (4). Pilot pressure oil in line

(4) shifts the spool in the left track control valve right, allowing flow of main system oilto the left track motor. This moves the left track motor in the FORWARD direction. The

machine turns to the right in a "PIVOT" turn.

The functions of the oil passages inside spools (5) and (7) are:

1. Modulation of the flow of oil and pressure between passage (14) and oil lines

(4) and (8) when spool (7) is moved to start or stop the flow of oil between them.

2. To keep an open connection for oil return to tank at all times for correct

operation of the pressure reducing characteristics of valves (1) and (11).

When spool (2) is in the NEUTRAL position, the oil that goes through the drilled

passages in spools (5) and (7) goes to tank through passage (26).

Right Spot Turn

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Cross Section Of Speed Control And Steering Valve (RIGHT SPOT Turn)

(4) Oil line for pilot oil to the left track main control valve for FORWARD movement. (6) Pilot valve

(controls direction of rotation for left and right track). (7) Spool in valve (6) (controls direction of righttrack-steering). (9) Oil line for pilot oil to the right track main control valve for REVERSE movement. (10)

Spool in valve (11). (11) Pilot valve (controls flow and pressure of pilot oil to the main control valves for

machine movement in the FORWARD direction). (14) Oil passage. (21) Oil chamber. (25) Oil chamber.

(27) Spring (outer). (28) Spring n (inner).

Spool (10) is pushed down for FORWARD movement of the machine. Movement of the

steering control lever all the way to the right moves spool (7) down against the force of springs (27) and (28) until a connection is made between passage (14) and chamber (21).

Line (9) connects chamber (21) to the main control valve for right track. Pilot pressure oil

in line (9) shifts the spool in the right track control valve left, allowing flow of mainsystem oil to the right track motor. This moves the right track motor in the REVERSE

direction.

At the same time, pilot oil in passage (14) flows through chamber (25) and line (4). Pilot

pressure oil in line (4) shifts the spool in the left track control valve right, allowing flow

to main system oil to the left track motor. This moves the left track motor in theFORWARD direction.

With the right track moving in the REVERSE direction and the left track moving in the

FORWARD direction, the machine makes a "SPOT" turn to the right.

Reverse Direction

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Cross Section Of Speed Control And Steering Valve

(REVERSE Direction)

(1) Pilot valve (controls flow and pressure of pilot oil to the main control valves for machine movement in

the REVERSE direction). (2) Spool in valve (1). (3) Oil line for pilot oil to the left track main control valve

for REVERSE movement. (9) Oil line for pilot oil to the right track main control valve for REVERSEmovement. (21) Oil chamber. (22) Inlet line (supply oil to pilot valves). (23) Oil chamber. (24) Oil chamber

[connected to inlet (22)]. (26) Oil passage. (29) Spool. (30) Spring.

When the foot pedal for REVERSE movement is pushed down, spool (2) moves against

the force of spring (30). Spool (29) moves down to make a connection for pilot pressure

oil between chamber (24) and passage (26). Oil fills passage (26) and goes from passage

(26) to chambers (21) and (23). Line (3) makes a connection for oil flow between

chamber (23) and the main control valve for left track. Line (9) makes a connection for oil flow between chamber (21) and the main control valve for right track. Pilot pressure

oil in lines (3) and (9) shifts the spools in both track valves left, allowing flow of main

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system oil to the track motors. This moves both track motors in the REVERSE direction.

The machine moves in REVERSE.

Track Control Valves

Track Control Valve(Right Track Valve Shown)

(1) Overspeed valve (REVERSE). (2) Oil line for main system oil to motor for left track, FORWARD. (3)

Oil line for main system oil from the front pump. (4) Inside passage. (5) Oil line for main system oil to

motor for left track, REVERSE. (6) Oil passage. (7) Overspeed valve (FORWARD). (8) Springs. (9) Spool.

(10) Main control valve for left track. (11) Oil passages (tank). (12) Oil chamber. (13) Oil chambers. (14)

Oil chamber. (15) Pilot oil line to main control valve for left track, FORWARD.

The control valves for tracks (left and right) are the same. The oil flow to the right track control valve comes from the output of the front bent-axis piston pump. The oil flow to

left track control valve (10) through oil line (3) comes from the output of the rear bent-

axis piston pump. The characteristics and operation of both left and right track control

valves are similar to the characteristics and operation of the other main control valves inthe front and rear valve banks. (See Boom, Bucket And Stick Control for explanation of

oil flow, load check valves, line relief valves and makeup valves). The difference

between the track control valves and the others is the addition of overspeed valves (1)

and (7).

System Oil Flow (Right Track Forward)

In the other control valves, passage (11) and chamber (12) are connected when pilot oil

pressure in line (15) moves spool (9). This allows main system oil from line (3) out line

(2). Return oil is free to go to tank. However, in the track valves, passage (6) is between

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passage (11) and chamber (12). Movement of spool (9) connects passage (6) to chamber

(12). Return oil in line (5) and chamber (12) can not go directly to tank passage (11). Itmust go from chamber (12) through passage (6) and then to tank passage (11).

Passage (4) inside of left track control valve (10) makes a connection between chamber

(14) and the end of overspeed valve (7). When spool (9) is moved to the right, aconnection is made between chambers (13) and (14) for main system oil from line (3).

The main system oil in chamber (14) goes to the right track motor through line (3). At the

same time, pressure goes through the inside passage from chamber (14) to the end of

overspeed valve (7). Movement of overspeed valve (7) opens a connection between

passages (6) and (11). Return oil, from the right track motor, in line (5) can go to tank

from chamber (12) through passage (6) to passage (11).

When the machine moves down a grade fast enough to cause the motor to overspeed,there will be a decrease in pressure in line (2) and chamber (14).

When oil pressure in line (2) and chamber (14) decreases to about 1200 kPa (175 psi), the

force of spring (8) moves overspeed valve (7) right. This stops the flow of return oil to passage (11). The restriction of the return oil causes an increase in oil pressure in line (5)

and a resistance to the rotation of the motor. There is a decrease in motor rpm until its

input flow rate is the same as the rate of output flow from the pump. In this way, themotor can not turn faster than the pump. Pressure in line (2) is held at more than 1200

kPa (175 psi) and cavitation at the pumps is not possible.

Blocker Valve


(1) Blocker valve. (2) Outlet (to main control valve for left track. (3) Inlet (pilot pressure from shuttle

valve). (4) Inlet (main system oil from main control valve for right track).

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(1) Blocker valve. (2) Outlet (to main control valve for left track. (3) Inlet (pilot pressure from shuttle

valve). (4) Inlet (main system oil from main control valve for right track). (5) Outlet (to tank).

Blocker Valve

When the pilot valve for swing is activated, pilot oil goes to the main control valve for swing and to a shuttle valve. Since the main control valve for swing is the first valve in

the rear main control valve group, all of the flow from the rear pump could be used to

turn the upper structure. If one of the track valves was activated at the same time therewould be no oil flow or pressure to turn the left track motor. To prevent this from

happening, pilot oil from the shuttle valve goes in inlet (3) on blocker valve (1) and

moves the stem to the left. This opens a passage from inlet (4) to outlet (2) for main

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system oil from the front pump to go to the main control valve for the left track. Both

tracks will move but at a reduced speed.

Track Motors

225D Track Motors

Track Motor (Typical Example)

(1) Pin (pivot). (2) Pistons (seven). (3) Barrel. (4) Port plate. (5) Case. (6) Head. (7) Control slot. (8) Oil

passage (pin lubricating). (9) Control slot. (10) Cover. (11) Nut. (12) Bearing. (13) Shim. (14) Ring. (15)

Bearing. (16) Shaft. (17) Retaining plate.

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Two track motors (20) and (23) are the same. They are fixed displacement, bent-axis

piston motors. Each motor is operated by pressure oil from one of the two variabledisplacement pumps (the two pump-to-motor circuits are separate at all times). A change

in the direction of oil flow through a motor will not change the amount of output torquefrom the shaft of the motor.

Oil flow through the motor can be in either direction. A change to the direction of oil

flow changes the direction of rotation of barrel (3), piston (2) and drive shaft (16).

The components of the motor that turn are drive shaft (16), nut (11), retaining plate (17),

pistons (2) and barrel (3). The parts that do not turn are head (6), housing (5), port plate

(4), shims (13), ring (14) and cover (10).

Oil from the pump flows through the combiner and control valve for the right or left

track. The pressure oil then flows into either control slot (7) or (9) (depending on thedirection of track rotation) in head (6); through the same control slot (7) or (9) in port

plate (4) and into the cylinders [in barrel (3)] that are over the inlet control slot.

The cylindrical piston heads are held in sockets in shaft (16) by retaining plate (17).Pistons (seven) (2) are positioned in barrel (3). Barrel (3) rotates about pivot pin (1)

which is at a fixed angle of 40° to the axis of shaft (16). Because of this bent-axis

arrangement between pistons and barrel, the seven pistons (2) move in and out of their cylinders as pressure oil leaves and enters the cylinders. This forces the piston, and in

turn shaft (16) and barrel (3), to rotate.

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As shaft (16), piston (2) and barrel (3) continue to rotate, the piston reaches top center

(fully retracted position). At the same time, the cylinder begins to overlap the control slot(outlet passage) (9) or (7). At this point the piston starts to move down. In moving down,

the piston pushes oil out of the cylinder into control slot (9) or (7) of port plate (4),through control slot (9) or (7) of head (6) and on to the control valve and tank.

The ball (head) of center pin (1) is the pivot point for barrel (3). Oil passage (8) provides

lubricating oil to a drilled passage in pin (1). The oil then flows to the pivot pin socket

and on through passages to bearings (12) and (15). This oil drains from case (5) through

port (18).

229D - 231D Track Motors

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Track Motor (Typical Example)

(1) Cover. (2) Flange. (3) Port for case drain. (4) Shaft. (5) Retaining plate. (6) Pin (pivot). (7) Piston

(seven). (8) Barrel. (9) Housing. (10) Adjustment screw. (11) Head. (12) Port plate. (13) Centering pin. (14)Ring. (15) Bearing. (16) Shim. (17) Bearing. (18) Ring. (19) Disc. (20) Disc.

Track Motors And Brakes (Typical Example)

(27) Right track brake. (28) Right track motor. (29) Left track motor. (30) Left track brake. (31) Track

brake line. (32) Drain lines. (33) Pump oil lines. (34) Pump oil lines. (35) Track brake line.

When the machine is traveling, turning or both, pilot oil flows through line (31) to track brake (30) and line (35) to track brake (27). The pilot oil then releases the track brake

allowing track motors (28) and (29) to operate.

Depending on desired movement (FORWARD or REVERSE) pump oil flows to and

from the motors through lines (33) (left track motor) and lines (34) (right track motor).

Case drain oil returns to tank through lines (32).

The two track motors are identical. They are fixed displacement, bent-axis piston motors.

Each motor is operated by pressure oil from one of the two variable displacement pumps(the two pump-to-motor circuits are separate at all times). A change in the direction of oil

flow through a motor will change the amount of output torque from the shaft of the

motor.

Oil flow through the motor can be in either direction. A change to the direction of oil

flow changes the direction of rotation of barrel (8), piston (7) and drive shaft (4).

The components of the motor that turn are drive shaft (4), ring (14), retaining plate (5), pistons (7) and barrel (8). The parts that do not turn are head (11), housing (9), port plate

(12), shims (16), ring (18) and cover (1).

Oil from the pump flows through the combiner and control valve for the right or left

track. The pressure oil then flows through inlet ports into either control slot (21) or (22)(depending on the direction of track rotation) in head (11); through similar control slots(23) or (24) in port plate (12) and into the cylinders [in barrel (8)] that are over the inlet

control slot.

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Head (End view)

(11) Head. (21) Control slot. (22) Control slot.

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Port Plate [Viewed from head (11)]

(12) Port plate. (23) Control slot. (24) Control slot. (25) Groove. (26) Slot.

The cylindrical piston heads are held in sockets in shaft (4) by retaining plate (5). Pistons

(seven) (7) are positioned in barrel (8). The barrel rotates about pivot pin (6) which is at a

fixed angle of 24 degrees to the axis of shaft (4). Because of this bent-axis arrangement between shaft and barrel, the seven pistons move in and out of their cylinders as pressure

oil leaves and enters the cylinders. This forces the piston, and in turn shaft (4) and barrel

(8), to rotate.

As shaft (4), piston (7) and barrel (8) continue to rotate, the piston reaches top center

(fully retracted position). At the same time, the cylinder begins to overlap the control slot

(outlet passage) (23) or (24). At this point the piston starts to move down. In moving

down, the piston pushes oil out of the cylinder into control slot (23) or (24) of port plate

(12), through control slow (21) or (22) of head (11) and on to the control valve and tank.

Oil from the case drain provides lubricating oil. Oil flows through groove (25) and slot

(26) in plate (12), through the center of adjustment screw (10) and disc (19) to a drilled

passage in pin (6). The ball (head) of center pin (6) is the pivot point for barrel (8). Oil

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229D And 231D Cross Section Of Track Brake

(1) Cavity. (2) Housing. (4) Springs. (5) Plates (six). (6) Discs (five). (7) Adapter. (8) Piston. (9) Coupler.

Each track motor has a brake (10) on the output shaft of the motor. At all times, adapter (3), for 225D, or coupler (9), for 229D and 231D, connects the output shaft of the motor

and the input shaft of the final drive. The machine can not move when the adapter (3) [or

coupler (9)] is stopped from turning. Housing (2) is connected to the final drive housing

with bolts and can not turn. Teeth on the outer circumference of the plates (5) engage

with teeth on the inner bore of housing (2). Plates (5) are held by housing (2). Teeth onthe inner circumference of discs (6) engage with teeth on the outer circumference of

adapter (3) [or coupler (9)]. The adapter or coupler can not turn when discs (6) and plates

(5) are held together by the force of springs (4).

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Track Brake (Typical Example)

(10) Track brake.

Normally, the force of springs (4) push against adapter (7) and piston (8) to hold the

plates and discs together. When a travel pedal is activated, cavity (1) gets oil pressurefrom the pilot system oil.

Oil pressure in cavity (1) moves piston (8) against adapter (7) to compress springs (4).This releases the force on discs (6) and plates (5). When the force holding the discs and

plates together is released, adapter (3) [or coupler (9)] is free to turn when the track motor

turns to turn the input shaft of the final drive.

Final Drives

When the final drives are disconnected, the machine has no brakes. To

disconnect the final drive with the machine on a slope would allow a

"runaway" condition. Before the final drives are disconnected, either

put blocks in the path of the tracks or connect the towbar to the towing

machine. After towing the machine to the desired location, either block

both tracks (front and rear), keep it connected to the towing machine or

engage the final drives. If the failure is in a final drive, engaging the

final drive may not insure that the brake on the failed final drive will be

effective. If one of the gears has lost some of its teeth, the sprocket may

be rotated even though the brake is engaged and the disconnectmechanism is engaged.

225D Final Drives

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Cross Section Of Final Drive

(1) Track sprocket. (2) Gear. (3) Bracket. (4) Retainer. (5) Spline.

The adapter in the track brake connects input gear (2) and the output shaft of the track motor. As gear (2) rotates, spline (5) starts in motion a series of gears which turn sprocket

(1).

To move the machine when the engine is stopped and not cause damage to the track

brake and motors, there must be a separation between the final drive gears and the track motors. Remove bracket (3) and back out retainer (4) approximately 50.8 mm (2 in)[height of bracket (3)].

After the retainer is backed out, there is no connection between the series of final drive

gears and the track motor and brake. The machine can now be moved.

229D - 231D Final Drives

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Cross Section Of Final Drive

(1) Track sprocket. (2) Rod. (3) Coupling. (4) Springs (twenty). (5) Pinion. (6) Spline. (7) Nut. (8) Plug.

The coupler in the track brake connects coupling (3) and the output shaft of the track

motor.

Rod (2) goes through coupling (3) and pinion (5). Nut (7) on rod (2) holds coupling (3)against pinion (5). The pinion and coupling have matched serrations (sawtooth

configuration) that allows the coupling to drive the pinion. As pinion (5) rotates, spline(6) starts in motion a series of gears which turns sprocket (1).

To move the machine when the engine is stopped and not cause damage to the track

brake and motors, there must be a separation between the final drive gears and the track

motors. Remove plug (8) and turn nut (7) counterclockwise. As nut (7) is loosened,compressed springs (4) start to relax and force apart coupling (3) and pinion (5). When

the respective serrations on the coupling and pinion clear each other, there will be no

connection between the series of final drive gears and the track motor and brake. Nut (7)

will clear approximately 50.8 mm (2 in) of rod (2) before the drive motor is disconnected

from the final drive gears.

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Schematic For Swing Control


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Schematic For 225D (Earlier Style Shown)

(1) Bent-Axis Piston Motor. Installed to give movement to the upper structure (swing).

(2) Swing Orifice Solenoid Valve. When electrically energized, this valve opens a restricted opening

(orifice) between lines (4) and (5) to give a slower stop.

(3) Line Relief Valve For Swing. This valve limits the pressure in the swing circuits to 18 300 ± 345 kPa

(2650 ± 50 psi) for 225D and 229D, to 20 000 ± 345 kPa (2900 ± 50 psi) for the 231D.

(4) Oil line for main system oil from control valve for swing motor, swing RIGHT.

(5) Oil line for main system oil from control valve for swing to swing motor, swing LEFT.

(6) Makeup Valves.

(7) Crossover Valves For Boom And Stick Operation. These valves are controlled by the pilot valves for

boom and stick movement. They control the flow of oil from the front pump (stick crossover) and rear

pump (boom crossover). When they are activated, the flow from one pump combines (goes together) with

the flow from the other and boom and /or stick speed of operation is increased.

(8) Main Control Valve For Stick. This valve is controlled by the pilot valve for stick movement. It controls

the flow of oil from the rear pump to the stick cylinder.

(9) Main Control Valve For Left Track. This valve is controlled by the pilot valve for left track movement.

It controls the flow of oil from the rear pump to the left track motor.

(10) Main Control Valve For Swing. This valve is controlled by the pilot valve for swing movement. It

controls the flow of oil from the rear pump to the swing motor.

(11) Blocker Valve. When the swing circuit is activated, this valve is controlled by pilot pressure oil from

the shuttle valve. It controls the flow of main system oil from the main control valve for right track (front

pump) to the main control valve for the left track.

(12) Oil line for pilot oil to blocker valve from shuttle valve.

(13) Shuttle valve. This valve allows the swing pilot pressure signal to open the blocker valve.

(14) Oil line for pilot pressure oil to main control valve for swing LEFT.

(15) Oil line for pilot pressure oil to main control valve for swing RIGHT.

(16) Oil line for supply of pilot pressure oil to pilot control valves.

(17) Oil line for main system oil from the combiner valve (rear pump) to the main control valves for swing,left track, stick and boom crossover.

(18) Pilot Control Valve. Manually operated for control of pilot pressure oil to the main control valves for

the stick and swing.

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Excavator

(22) Upper structure.

The upper structure of the excavator is turned 360° on the undercarriage by bent-axis

piston motor (1). The oil supply for the swing circuit comes from the bent-axis piston

pump (19) through line (17) and main control valve (10) for swing. The return passagesin main control valve (10) are common with the return oil passages for control valve (9)

for the left track, control valve (8) for the stick, and boom and stick crossover controlvalve (7).

All of the output of oil from pump (19) is sent to control valve (10) through line (17).

Control valve (10) uses supplied oil to control swing RIGHT movement through line (4)

and swing LEFT movement through line (5).

Swing Motor And Brake

(1) Bent-axis piston motor. (3) Relief valve for swing circuit. (23) Swing brake.

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The operation of control valve (10) for swing is similar to the operation of the other

control valve groups. (See Boom, Bucket And Stick Control section for an explanation of valve operation). There is a makeup valve (6) for each output oil line to the swing motor.

Movement of the spool in control valve (10) is controlled by the pressure of pilot system

oil in pilot lines (14) and (15). Modulation of oil pressure in lines (14) and (15) is done by the spool in pilot valve (18). Oil pressure to the inlet of the pilot valve, must always be

approximately 2300 kPa (335 psi) while the engine is running. Pilot valve (18) has the

capacity to take the 2300 kPa (335 psi) inlet oil pressure and send oil to either line (14) or

(15) at pressures between zero and 2300 kPa (335 psi). Modulation of the pressure in

lines (14) and (15) will give partial movement of oil from pump (19) to swing motor (1).

The swing circuit is protected by its own relief valve. There are two line relief valves inthe group. One valve protects the circuit during swing RIGHT movement and the other

valve protects the circuit during swing LEFT Movement.

When valve (10) is in NEUTRAL and swing rotation causes the swing motor to pump oil

through line (4) or line (5), swing relief valve (3) will open when oil pressure is

approximately 18 300 kPa (2650 psi) for the 225D and 229D and to 20 000 kPa (2900

psi) for the 231D. The oil that is dumped by the relief valve goes to the line that is not

pressurized. The 18 300 kPa (2650 psi), for the 225D and 229D and 20 000 kPa (2900 psi) for the 231D, pressure in line (4) or line (5) is used as a brake to stop the rotation of

upper structure (22).

Swing Orifice Valve

Top View Front Main Control Valve(2) Swing orifice valve.

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Right Console

(24) Switch.

Swing orifice valve (2) is electrically operated. By moving switch (24) to the right, valve

(2) opens an orifice between lines (4) and (5).

During a swing operation where a slower and smoother stop is important, switch (24)energizes valve (2) which in turn diverts part of the pressurized oil to the line that is not

pressurized.

Swing Motor

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Cross Section Of Swing Drive

(23) Swing brake. (25) Input shaft. (26) Output shaft.

Swing motor (1) works the same as the track motors. (See Speed And Direction Control

for explanation of motor operation).

The output shaft of the swing motor is connected to input shaft (25) of the swing drive.

The output shaft of the swing motor turns shaft (26) through a series of gears.

Swing Brake And Swing Lock Pin

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View Of Right Side Of Operator's Seat (Earlier Style Shown)

(27) Brake lever. (28) Lock pin lever.

A manually-activated, expanding shoe-type brake (23) on the shaft of one of the gears

gives added braking capacity. The manual brake SHOULD NOT be used to stop rotation.Move the swing control lever to NEUTRAL and use the restriction of main system oil to

stop rotation of the upper structure.

Hand control lever (27) for the swing brake is at the right side of the operator's seat. To

adjust for swing brake wear turn the end of the handle on the brake lever.

To prevent rotation of the upper structure, the swing lock pin can be engage when the

upper structure is aligned with the track in the FORWARD or REVERSE direction.

NOTICEEngage the swing lock pin only when the upper structure is aligned

with the track. DO NOT attempt to engage the swing lock pin when the

upper structure is rotating.

To engage the lock pin, push lever (28) down and forward. To disengaged the lock pin, pull lever (28) up and back.

Automatic Engine Speed Control(Attachment)

Introduction

The purpose of the Automatic Engine Speed Control is to gain fuel savings by reducing

engine speed during "non-use or dead time" periods. Examples of "non-use or dead time"

periods are: the time waiting for a truck to position itself for loading, the time waiting for

a crew to set a pipe in a trench, or the time the operator takes when stopping work to talk

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to someone. Basically, "non-use or dead time" is any time the machine is at rest (not

working).

The Automatic Engine Speed Control has two modes of operation. Mode 1 is an idling

speed mode. This speed should not be confused with low idle rpm. Idling speed mode is a

higher rpm. Mode 2 is an economy operation mode. This intermediate speed is used whenfull engine power is not required to do the work. See chart below for specific speeds

(rpms).

Left Hand Console (Earlier Style Shown)

(1) Mode switch.

With mode switch (1) in the Mode 1 or Mode 2 position, Automatic Engine SpeedControl decreases engine speed to a preset idling speed setting during periods when there

is no operator demand for engine power. The operator's demand for engine power is

determined by sensing the pilot pressure from the four pilot control valve functions

(boom, bucket, stick and swing) and electrical signals from the auxiliary and travel

functions.

When mode switch (1) is in the Mode 1 position (left) and the governor control lever is pulled back into the high idle position, engine speed is decreased to the preset idling

speed setting after three seconds when the highest pilot pressure is below 140 kPa (20

psi) and there is no input from the travel or auxiliary circuits. Engine speed returns to the

high idle setting when pilot pressure increases above 140 kPa (20 psi) or the auxiliary or

travel circuits are activated.

When mode switch (1) is in the Mode 2 position (right) and the governor control lever is

pulled back into the high idle position, the engine speed is decreased to the preset idling

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speed setting after three seconds when the highest pilot pressure is below 140 kPa (20

psi) and there is no input from the travel or auxiliary circuits. Engine speed goes to a preset intermediate speed setting when the highest pilot pressure is above 140 kPa (20

psi) or an auxiliary circuit is activated. Engine speed will go to the high idle setting whenthe travel circuit is activated in Mode 2.

When the mode switch is in the OFF position (center), engine rpm is controlled by the

position of the governor control lever.

The Automatic Engine Speed Control linkage in the operator's station is preset to

determine the idling and intermediate speed settings. The governor control lever does not

move when the engine speed changes. If the governor control lever is not pulled all the

way back into the high idle position, the Automatic Engine Speed Control will stilloperate. The high idle setting that the speed control returns to is then determined by the

position of the governor control lever.

System Operation

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Operator's Platform

(1) Solenoid. (2) Spring assembly. (3) Control module. (4) Line. (5) Cylinder group. (6) Shaft assembly.

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Right Hand Console

(2) Spring assembly. (5) Cylinder group. (6) Shaft assembly. (7) Rod end (intermediate speed). (8) Rod end

(idling speed). (9) Governor cable assembly.

Bottom View Of Operator's Platform

(4) Supply oil line to solenoid. (10) Hydraulic and directional lock valve. (11) Pilot oil supply line.

Cross Section Of Cylinder Group

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(5) Cylinder group. (12) Spacer. (13) Piston. (14) Cavity. (15) Cylinder rod. (16) Cylinder rod. (17) Cavity.

(18) Piston. (19) Spacer.

Cross Section Of Spring Assembly

(2) Spring assembly. (20) Rod assembly. (21) Spring.

NOTE: Ports C1 and C2 are stamped on the solenoid assembly. Ports P1 and P2 arestamped on the cylinder group.

Mode 1 Operation

Oil supply to solenoid (1) comes from pilot oil supply line (11) to hydraulic and

directional lock valve (10). Solenoid supply oil line (4) is connected to the pilot supply

line before the lock valve. This allows the Automatic Engine Speed Control to function,even though the lock valve may be in the LOCK position.

Solenoid (1) directs pilot oil to cavity (14) or (17) in cylinder group (5). When there is no

electrical signal to it, solenoid (1) rests in the closed centered position. Supply oil fromline (4) is blocked and the two solenoid ports (C1 and C2) to cylinder group (5) are open

to tank.

When control module (3) sends an electrical signal to the solenoid for Mode 1 operation,

the solenoid energizes and pulls it's cartridge assembly inward. This opens a path for pilot

oil to flow through port C2 and the line to cylinder group port P2. Pilot oil fills cavity(17) in the cylinder group and moves piston (18) until it rests against spacer (19). As the

piston moves, it pulls cylinder rod (16) with it.

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As rod (16) moves, it pulls the shaft assembly arm it is fastened to. This pivots shaft

assembly (6) and the other lower arms clockwise. Governor cable assembly (9) is pushed back, reducing engine rpm to the preset idling speed setting. Cylinder rod (15) is pushed

into the cylinder body, but has no effect on system operation. The case of springassembly (2) fastened to the top shaft assembly arm moves clockwise. Since spring rod

(20) is held stationary by the governor control locking mechanism, spring (21) is

compressed as the spring case moves.

There are now two forces working on shaft assembly (6): the pilot oil pressure in cavity

(17) that moved it clockwise and compressed spring (21) trying to pull it

counterclockwise. When there is a demand for engine power, solenoid (1) is de-

energized. The cartridge assembly returns to the closed centered position. Pilot oil in

cavity (17) now goes to tank through the solenoid. Spring (21) pulls the shaft assembly

arm, which rotates shaft assembly (6) counterclockwise. The lower arm fastened to

governor cable assembly (9) rotates. This pulls the cable back to the high idle setting.

Rod end (8) is fastened to the shaft assembly arm. It is used to adjust idle speed setting.

Turn the rod end to change rod length. Increasing rod length will decrease the amount of

engine rpm lowered. Decreasing rod length will increase the amount of engine rpm

lowered.

Mode 2 Operation

At first, the operation of Mode 2 is the same as Mode 1. When the electrical signal fromcontrol module (3) is sent to solenoid (1), the solenoid energizes, causing cylinder rod

(16) to move governor cable assembly (9) to the preset idle speed setting.

In Mode 2, when a demand for engine power (other than travel) occurs, the electrical

signal to the solenoid changes instead of stopping. An electrical signal is sent to the

solenoid to energize the other side. This cause the cartridge assembly to be pushed out.

This opens a path for pilot oil to flow through port C1 and the line to cylinder group port

P1. Pilot oil fills cavity (14) in cylinder group (5) and moves piston (13) until it rests

against spacer (12).

At the same time, pilot oil from cavity (17) is allowed to go to drain. Compressed spring

(21) pulls the shaft assembly and arms counterclockwise (as in Mode 1). Shaft assembly

(6) pivots until cylinder rod (15) is pulled against piston (13), stopping rotation. Governor

cable assembly (9) has now been pulled to the intermediate speed setting.

Rod end (7) fastened to the shaft assembly lever is used to adjust intermediate speed

setting. Turn the rod end to change rod length. Increasing rod length will decrease the

amount of engine rpm lowered. Decreasing rod length will increase the amount of engine

rpm lowered.

Component Operation

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Governor Lever And Cable Assembly

Right Hand Console

(1) Governor lever. (2) Spring assembly. (3) Shaft assembly. (4) Bracket assembly. (5) Cylinder group. (6)

Governor cable assembly. (7) Governor control locking mechanism.

The mechanism that controls movement of the governor cable assembly is installed in the

right arm of the operator's seat. Bracket assembly (4) holds shaft assembly (3). Shaft

assembly (3) pivots in the bracket assembly. The shaft assembly has three arms on the

bottom and one on the top. The three lower arms are fastened to governor cable assembly

(6) and the two rods from cylinder group (5). The top arm is fastened to the case of springassembly (2). Spring assembly (2) contains a spring that collapses (loads) when it's rod isextended. The extendable rod from the spring assembly is fastened to governor control

locking mechanism (7). Governor lever (1) is also fastened to the locking mechanism.

Governor locking mechanism (7) operates so that a load put on it from the governor lever

mounting side allows the locking mechanism to move. However, any load put on it from

the spring assembly mounting side locks the mechanism in place. This assures that during

normal operation, no outside load on the governor cable assembly will change the enginerpm setting.

During normal machine operation, governor lever (1) is pulled back to increase engine

rpm. As the governor lever pivots, it moves the governor locking mechanism. The

locking mechanism pulls on the spring rod. The resistance to movement is not enough to

pull the rod out of the spring assembly. Spring assembly (2) moves, pulling the top armof the shaft assembly. Shaft assembly (3) pivots counterclockwise in the bracket. The bottom arms pull governor cable assembly (6) (increasing engine rpm) and extend both

rod assemblies from cylinder group (5).

Implement Circuit Inputs

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(8) Stick/swing check valve group. (9) Line. (10) Line. (11) Boom/bucket check valve group. (12) Check

valves (eight). (13) Implement circuit pilot pressure lines.

Check Valve Group

(8) Stick/swing check valve group. (11) Boom/bucket check valve group. (12) Check valves.


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(10) Line. (14) Manifold. (15) Tee. (16) Differential pressure switch. (17) Line. (18) Travel pressure

switch.

The implement circuit has eight inputs: boom RAISE, boom LOWER, bucket OPEN, bucket CLOSE, stick IN, stick OUT, swing RIGHT and swing LEFT. Each implement

input has a pilot pressure oil line from the pilot control valves to the main control valves.

Each pilot pressure oil line is teed into by a separate line (13) that goes to check valve

groups (8) and (11). Four lines (13) go to each check valve group. Each check valve

group contains four check valves (12), one for each implement function. When an

implement is operated, pilot signal oil pressure flows through pilot line (13) for thatfunction and opens its check valve in the check valve group. Pilot signal oil flows into the

common passage in the valve body. Signal pressure holds the other three check valves

closed. This prevents leakage into the other pilot lines. Signal pressure from stick/swing

check valve group (8) goes through line (9) to boom/bucket check valve group (11). If

two or more implement functions are being used at the same time, the check valves ineach group resolve the highest pilot signal oil pressure. The highest signal resolved

pressure is then sent through line (10) to pressure switch manifold (14). Pilot signal oilfills the cavity in the manifold. Pilot signal pressure is felt on the end of differential pressure switch (16).


(18) Travel pressure switch. (19) Control module. (20) Solenoid. (21) Brake release oil line.

Differential pressure switch (16) has pilot signal pressure at the manifold end and tank

pressure from line (17) at the other end. The differential switch is looking for a 140 kPa

(20 psi) difference between tank and signal pressure. When signal pressure reaches a

pressure 140 kPa (20 psi) above tank pressure, switch (16) opens and breaks the electrical

signal to control module (19). The loss of an electrical signal tells the control module toshift solenoid (20) to the closed center position. This provides a path for any pressure oil

in cylinder group (5) to go to tank. Engine speed returns to the high idle setting (Mode 1)or intermediate speed setting (Mode 2) before the implement moves.

The engine speed is able to return to the speed setting before the implement moves

because differential pressure switch (16) needs only a 140 kPa (20 psi) rise in pilot

pressure (above tank pressure) to open the switch. This stops the electrical signal to the

control module. The same pilot pressure is sent to the main control valve for that

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implement function. The main control valves need 415 to 550 kPa (60 to 80 psi)

(depending on implement) of pilot pressure before the spool will move.

When an implement operation stops, check valve (12) for that function closes. This

causes a loss of pilot signal oil pressure to differential switch (16). Pilot signal oil in

manifold (14) cavity goes to tank through an orifice in tee (15). Signal oil is constantlygoing to tank when the manifold cavity has pressure. The loss of oil through the orifice

does not affect differential pressure switch performance, as long as the orifice does not

become obstructed. When the pressure difference between signal and tank drops below

140 kPa (20 psi), switch (16) closes and an electrical signal is sent to control module

(19). After three seconds, a timing mechanism in the control module sends an electrical

signal to solenoid (20), telling it to shift. Pilot oil is sent to cylinder group (5), shifting it.

Engine speed goes to an idling speed.

Travel Circuit Inputs

The travel circuit has four inputs: FORWARD, REVERSE, RIGHT steer and LEFT steer.

The common line for each of these functions is signal line (21) to release the brakes.

When the machine is equipped with a travel alarm, electrical signal input to controlmodule (19) comes from brake oil pressure switch (18). If the machine is not equipped

with a travel alarm, a pressure switch is added to the brake signal line for signal input.

When a travel function is operated, oil pressure to release the brakes closes pressure

switch (18). An electrical signal is sent to control module (19). The control module stopsany electrical signal to solenoid (20). The solenoid shifts to the closed center position.

This provides a path for any pressure oil in cylinder group (5) to go to tank. Engine speedreturns to the high idle setting (Mode 1) or (Mode 2) before the machine moves.

The engine speed is able to return to the high idle setting before the machine moves

because the signal oil sent to release the brakes (before machine movement) also closes

pressure switch (18).

When a travel function stops, oil pressure to release the brakes stops. The loss of oil

pressure in signal line (21) allows pressure switch (18) to open. The electrical signal to

the control module stops. After three seconds, a timing mechanism in the control module

sends an electrical signal to solenoid (20), telling it to shift. Pilot oil is sent to cylinder

group (5), shifting it. Engine speed goes to an idling speed.

Auxiliary Circuit Inputs

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Electrical schematic

(22) Diode assembly. (23) ON input. (24) HIGH SPEED input.

Electrical schematic

(25) Diode assembly. (26) COUNTERCLOCKWISE rotation input. (27) CLOSE input. (28) CLOCKWISE

rotation input. (29) OPEN input.

The 225D, 229D and 231D auxiliary circuit inputs comes from clamshell, hammer or grapple attachments. The clamshell has OPEN (29) and CLOSE (27) electrical inputs.

The hammer has ON (23) and if equipped HIGH SPEED (24) electrical inputs. Thegrapple has OPEN (29), CLOSE (27), CLOCKWISE rotation (28) and

COUNTERCLOCKWISE rotation (26) electrical inputs. When an attachment with two

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or more inputs is added, the Automatic Engine Speed Control group adds diodes (22) or

(25) to the electrical harness. The diode acts as a resolver, taking the two or more possible electrical inputs down to a single electrical input. The single input is then sent to

control module (19).

When an auxiliary function is operated, an electrical signal is sent to control module (19).The control module stops any electrical signal to solenoid (20). The solenoid shifts to the

closed center position. This provides a path for any pressure oil in cylinder group (5) to

go to tank. Engine speed returns to the high idle setting (Mode 1) or intermediate speed

setting (Mode 2).

When an auxiliary function stops, the electrical signal to the control module stops. After

three seconds, a timing mechanism in the control module sends an electrical signal to thesolenoid, telling it to shift. Pilot oil is sent to cylinder group (5), shifting it. Engine speed

goes to an idling speed.

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225d Hyd Sys