Hydraulics IOE PPT

•Basics of Hydraulics•Basics of Hydraulics•Major applications in Earth Moving Equipment•Major Components of Hydraulic System •Hydraulic System DesignHydraulic System Design

Basics of HydraulicsyLIQUIDS HAVE NO SHAPE OF THEIR OWN.

They acquire the shape of any container Be‐cause of this oil in a hydraulic system They acquire the shape of any container. Be cause of this, oil in a hydraulic system will flow in any direction and into a passage of any size or shape.

LIQUIDS TRANSMIT APPLIED PRESSURE IN ALL QDIRECTIONS.LIQUIDS ARE PRACTICALLY INCOMPRESSIBLELIQUIDS ARE PRACTICALLY INCOMPRESSIBLE.LIQUIDS PROVIDE GREAT INCREASES IN WORK FORCE FORCE.

This principle helps you to stop a large machine by pressing a brake pedal.

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HOW A HYDRAULIC SYSTEMWORKSHOW A HYDRAULIC SYSTEM WORKS1 The PUMPwhich moves the oil1. The PUMPwhich moves the oil.2. The CYLINDER which uses the moving oil to do work.

h ld h l h l fl3. CHECK VALVES to hold the oil the oil flow.4. A RESERVOIR (and its Ancillaries) to store the oil.4 ( )5. The CONTROL VALVE directs the oil flow.6 The RELIEF VALVE protects the system from high 6. The RELIEF VALVE protects the system from high

pressures.G h fl d i i7. Gauges show flow and pressure at various points.

8. Accumulator (if fitted) smoothens the performance.9. Filters to separate the contamination.10. Prime mover to drive the pump.0. e ove to d ve t e pu p.



Drive unitDrive unitHydraulic systems are driven by motors (electrical Hydraulic systems are driven by motors (electrical motors, combustion engines).Electrical motors generally provide the Electrical motors generally provide the mechanical power for the pump in stationary hydraulicshydraulicsCombustion engines are generally used in mobile hydraulics


ADVANTAGESFLEXIBILITY‐Unlike the mechanical method of power transmission where the relative positions of the engine and work site must remain relatively

t t ith th fl ibilit f h d li li b d t l t constant with the flexibility of hydraulic lines, power can be moved to almost any location.MULTIPLICATION OF FORCE‐small forces can be used to move large f gloads.SIMPLICITY‐The hydraulic system has fewer moving parts, fewer points of wear And it lubri cates itselfwear. And it lubri‐cates itself.COMPACTNESS‐The hydraulic system can handle more horsepower for its size than either of the other systems.ECONOMY‐This is the natural result of the simplicity and compactness which provide relatively low cost for the power transmitted. Also, power and frictional losses are comparatively smallfrictional losses are comparatively small.SAFETY‐fewer moving parts such as gears, chains, belt and electrical contacts than in other systems. Overloads can be more easily controlled by

l f l h bl h h l d d h husing relief valves than is possible with the overload devices on the other systems.


DISADVANTAGESEFFICIENCY‐While the efficiency of the hydraulic system is much better than the electrical system it is system is much better than the electrical system , it is lower than for the mechanical trans‐mission of power.NEED FOR CLEANLINESS‐Hydraulic systems can be damaged by rust, corrosion, dirt, heat and breakdown g y , , ,of fluids. Cleanliness and proper maintenance are more critical in the hydraulic system than in the other critical in the hydraulic system than in the other methods of transmission.FIRE HAZARD D lFIRE HAZARD‐ Due to neglegence.


APPLICATIONSAPPLICATIONS










Major Components of Hydraulic Systemj p y y

ReservoirReservoirTankFiltFilters

PumpsValves

Check ValvesCheck ValvesDirectional ValvesR li f V lRelief Valves

Hydraulic accumulatorsCylinders/Motors


Hydraulic reservoiryThe reservoir in a hydraulic system fulfils several tasks.

It acts as an intake and storage reservoir for the hydraulic fluid required for operation of the hydraulic fluid required for operation of the system;It dissipates heat;It dissipates heat;It separates air, water and solid materials;I b il i b il d d i It supports a built‐in or built‐on pump and drive motor and other hydraulic components, such as

l l t tvalves, accumulators, etc.


H d li iHydraulic reservoirThe reservoir consists of

Reservoir bodyIntake and return linesB ffl d ti l tBaffle and separating plateVentilation and exhaustMagnetic plugMagnetic plug

The size of the reservoir depends onPump deliveryp yThe heat resulting from operationThe volume of liquidThe place of applicationThe circulation timeTh i f th i i t l ifi d b it h i l The size of the reservoir is not classified by its physical dimensions but its liquid capacityReservoir size (litres) = pump (litres/min) x 3( ) p p ( / ) 3


Volume of Reservoir

2 3 times delivery ofReservoir

2 - 3 times delivery of pump in 1 minute

Pump

FillerReturn Connection

Breather with filter

Pump

Return lineReturn line

Level indicatorAccess panelpanel

Suction line

Drain PlugBaffles

Strainer


Hydraulic filterReservoir AccessoriesHydraulic filter

The task of the filter is to reduce the contamination in the system to anacceptable level in order to protect the various components fromp p pexcessivewear.

Filler cap (breather cap)I h ld b i i h h l d b i h i hi h It should be air tight when closed, but may contain the air vent which filters air entering the reservoir to provide a gravity push for proper oil flow.

Oil level gaugeIt shows the level of oil in the reservoir without having to open the reservoir.

Intake filterIt is usually a screen that is attached to the suction pipe to filter the hydraulic oil.

Drain plugIt allows all oil to be drained from the reservoir. Some drain plugs are magnetic to help remove metal chips from the Some drain plugs are magnetic to help remove metal chips from the oil.


Reservoir AccessoriesBaffle plate

It is located lengthwise through the centre of the tank g gand is 2/3 the height of the oil level. It is used to separate the outlet to pump from the return li Thi i it fl i t d f th line. This ensures a circuitous flow instead of the same fluid being recirculated. The baffle prevents local turbulence in the tank allows The baffle prevents local turbulence in the tank, allows foreign material to settle, get rid of entrapped air and increases heat dissipation.

Suction and return linesThey are designed to enter the reservoir at points where air turbulence are least. They can enter the reservoir at the top or at the sides, but their ends should be near the bottom of the tank their ends should be near the bottom of the tank. If the return line is above the oil level, the returning oil can foam and draw in air.can foam and draw in air.


S ti d t liSuction and return lines

Suction line Return line


Reservoir AccessoriesHydraulic filters

The task of the filter is to reduce the contamination in the system to an acceptable level in order to in the system to an acceptable level in order to protect the various components from excessive wear.

CoolersIn hydraulic systems, friction causes energy losses when the hydraulic fluid flows through the lines and components.This causes the hydraulic fluid to heat up.To a certain extent, this heat is given off to the environment via the oil reservoir, lines and other componentsThe following cooling devices are available:Air cooler : difference in temperature of up to 25°Cp p 5possible.Water cooler : difference in temperature of up to 35°cpossible.pOil cooling by means of air fan cooler : when large quantities of heat must be dissipated.


Reservoir AccessoriesHeaters

Heating elements or flow preheaters are Heating elements or flow preheaters are used for heating and preheating hydraulic fluidfluid.Heaters are often required to ensure that optimum operating temperature is quickly optimum operating temperature is quickly attained.Thi i t th t th t i This is to ensure that once the system is started up, the hydraulic fluid quickly reaches the optimum iscositreaches the optimum viscosity.If the viscosity is too high, the increased f i i d i i l d friction and cavitations lead to greater wear.



Hydraulic PumpsHydraulic PumpsThe pump basically performs two functions:

It creates a partial vacuum at the pump inlet port. The vacuum enables the atmospheric pressure to force fluid from the reservoir into the pumpthe reservoir into the pump.The mechanical action of the pump traps this fluid within the pump cavities, transports it through the pump, and p p , p g p p,forces it into the hydraulic system.

It is often assumed that pumps create pressure, but the sole purpose of pumps is to create flow.Pressure is created by resistance to flow.A pump is a mechanism designed to produce the flow necessary for the development of pressure.It cannot itself produce pressure, since it cannot provide resistance to its own flow.


Hydraulic pumpsy p pThree basic types of hydraulic pump can be yp y p pdistinguished on the basis of the displacement volume:volume:Constant pumps

Fi d di l t lFixed displacement volumeAdjustable pumps

Adjustable displacement volumeVariable capacity pumpsVariable capacity pumps

Regulation of pressure, flow rate.


HYDRAULIC PUMP FAMILYHYDRAULIC PUMP FAMILYHYDRAULIC

PUMPS

U C UU C UPUMPS

GEAR VANE PISTON

FIXED VARIABLE

EXTERNAL INTERNAL FIXED VARIABLE AXIAL AXIAL

BENT AXIS BENT AXIS

RADIAL1/2/2010 Satya Narayan Shah 29

Hydraulic pumpsy p p

Pump ratingRated by the amount of fluid that can be displaced for each revolution of the pump shaftSpecified in cubic inches or cubic centimeter per revolution

Displacement is defined as the volume of oil moved or displaced during each cycle of a pump. There are two forms of displacement :• Non‐positive displacementp p• Positive displacementPositive displacement pumpPositive displacement pump

Delivers to the system a specific amount of fluid per stroke, revolution or cyclerevolution or cycle


Hydraulic pumps The centrifugal pumpis an example of theis an example of thenon‐positive aspect, iti l th

•Besides being positive displacement pumps, they are also categorized as either: simply moves the

fluid and allows forb k fl

either:•Fixed displacement pumps•Variable displacement pumps back flow.Variable displacement pumps

•Fixed displacement pumps move the same volume of oil with every cycle.

•This volume is only changed when theThis volume is only changed when the speed of the pump is changed.

•Variable displacement pumps can vary the volume of oil they move with each cycle - even at the same speedcycle even at the same speed.

•These pumps have an internal

Satya Narayan Shah 31

mechanism which varies the output of oil.1/2/2010

Fixed & Variable displacement pumpsFixed

Fixed displacement pumps move the same volume of oil with every cycle. y yThis volume is only changed when the speed of the pump is changedthe pump is changed.

VariableVariable displacement pumps can vary the volume of oil they move with each cycle even volume of oil they move with each cycle ‐ even at the same speed. These pumps have an internal mechanism which varies the output of oil.p


Types of hydraulic pumpsTypes of hydraulic pumpsMost pumps used on today’s systems are of three Most pumps used on today s systems are of three basic designs:• Gear pumps• Gear pumps• Vane pumpsPi • Piston pumps

All three designs work on the rotary principle; a rotating unit inside the pump moves the fluid


Gear pumpsGear pumpsThey are widely used because they are simple and y y y peconomical. While not capable of a variable displacement While not capable of a variable displacement, they can produce the volume needed by most systems using fixed displacement systems using fixed displacement. Often, they are used as charging pumps for larger

f h system pumps of other types.


External gear pumpGear pumps are fixed displacement pumps displacement pumps since the displaced volume which is volume which is determined by the tooth gap is not tooth gap is not adjustable.


EXTERNAL GEAR PUMPEXTERNAL GEAR PUMP

ANIMATIONANIMATION1/2/2010 Satya Narayan Shah 36

EXTERNAL GEAR PUMP CHARACTERISTICSEXTERNAL GEAR PUMP CHARACTERISTICS

Typical displacements to 250 cm3/rTypical displacements to 250 cm3/r

Typical pressures to 250 bar

Fixed displacement only


Fixed displacement onlyFixed displacement only

Good speed range, limited indirect


Good speed range, limited indirect drive capability, simple multiple assembliesdrive capability, simple multiple assemblies

Generally noisyGenerally noisy

Good contamination sensitivity

Poor serviceability

Good contamination sensitivity

Poor serviceabilityPoor serviceability

Compact, low weight

Poor serviceability

Compact, low weight

Low cost.Low cost.1/2/2010 Satya Narayan Shah 37

Internal gear pumpsThe internal gear pump also uses two gears, but now a spur gear is mounted inside a larger geara spur gear is mounted inside a larger gear.The spur gear is in mesh with one side of the larger

d b th di id d th th id b gear and both gears are divided on the other side by a crescent shaped separator. The drive shaft turns the spur gear, which drives the larger gear.g g


INTERNAL GEAR PUMPINTERNAL GEAR PUMP


INTERNAL GEAR PUMP CHARACTERISTICSINTERNAL GEAR PUMP CHARACTERISTICS



d d l l


d d l lFixed displacement only

Good speed range


Good speed rangeGood speed range

Simple multiple assemblies

Good speed range

Simple multiple assembliesp p

Low noise

p p

Low noise

Good contamination sensitivityGood contamination sensitivity

Poor serviceabilityPoor serviceability

Good fluid compatibility.Good fluid compatibility.1/2/2010 Satya Narayan Shah 40

VANE PUMPS•Vane pumps are fairly versatile pumps and can bedesigned as single, double, or even triple units.g g p•All vane pumps move oil using a rotating slotted rotorwith vanes fitted into the slots.with vanes fitted into the slots.Two types of vane pumps are most often used:Balanced Vane Pumps The rotor is driven by the drive shaft andBalanced Vane Pumps-The rotor is driven by the drive shaft and turns inside an oval rotor ring. The vanes are fitted into the rotor slots and are free to move in or out. The pump has two inlet ports, located opposite each other. And it has two outlet ports, also on opposite sides of the pump. Both sets are connected to a central inlet and outlet.

Unbalanced Vane Pumps- The unbalanced vane pump uses theUnbalanced Vane Pumps- The unbalanced vane pump uses the same basic principle of a turning rotor with vanes working inside a fixed rotor ring. However, the operating cycle only happens once each revolution. So this pump has only one inlet and one outlet port. Also, the slotted rotor is now set offside in a circular ring.


VANE PUMP PRINCIPLEVANE PUMP PRINCIPLE


Balanced vane pumpsThe balanced vane pump is strictly a fixed displacement type pump. In the balanced vane pump, the rotor is driven by the drive shaft and turns inside an oval rotor ring. The vanes are fitted into the rotor slots and are free to move in and out.Typical displacements to 200 cm3/rTypical pressures to 280 barTypical pressures to 280 barFixed displacement onlyP id i fProvides prime mover soft‐startSimple double assembliesLow noiseGood serviceabilityy


Balanced vane pumpsp p


BALANCED VANE PUMPBALANCED VANE PUMP


Unbalanced vane pumpUnbalanced vane pumpThe unbalanced vane pump can have a fixed or a variable displacement variable displacement. It uses the same basic principle of a turning rotor with vanes working inside a fixed rotor ring. However, the operating cycle only happens once , p g y y ppeach revolution. So this pump has only one inlet and one outer So this pump has only one inlet and one outer port.Al th l tt d t i t ff id i Also, the slotted rotor is now set offside in a circular ring.


Unbalanced vane pumpp p


Unbalanced vane pump


Unbalanced variable vane pumpUnbalanced variable vane pump


VARIABLE VANE PUMP PRINCIPLEVARIABLE VANE PUMP PRINCIPLE






VARIABLE VANE PUMPVARIABLE VANE PUMP


MULTIPLE VARIABLE VANE PUMPMULTIPLE VARIABLE VANE PUMP


FIXED VANE PUMP CHARACTERISTICSFIXED VANE PUMP CHARACTERISTICS


Typical pressures to 280 barTypical pressures to 280 bar

Fixed displacement onlyFixed displacement only

Provides prime mover soft‐startProvides prime mover soft‐start

Simple double assembliesSimple double assembliesp

Low noise

p

Low noise

Good serviceability.Good serviceability.Good serviceability.Good serviceability.


VARIABLE VANE PUMP CHARACTERISTICSVARIABLE VANE PUMP CHARACTERISTICS

Typical displacements to 10

/

Typical displacements to 10

/cm3/r


cm3/r




Simple multiple assembliesSimple multiple assemblies

Range of pump controls


Range of pump controlsg p p

Low noise

g p p

Low noise

Low cost.Low cost.


Piston pumpsPi f f d d h d li Piston pumps are often favoured on modern hydraulic systems which use high speeds and high pressures.

l dHowever, piston pumps are more complex and more expensive than the other two types. They can be designed for either fixed or variable displacement.Most piston pumps are either:• Axial piston pumpsp p p• Radial piston pumpsAxial piston means that the pistons are mounted in lines Axial piston means that the pistons are mounted in lines parallel with the pump's axis (a line down the centre).R di l i t th t th i t t Radial piston means that the pistons are set perpendicular to the pump's centre like the sun's rays.


Piston pumps ‐ introductionp p


Axial piston pump


Axial piston pumpAxial piston pump








Axial piston pump


Axial piston pump


FIXED AXIAL PISTON PUMP CHARACTERISTICSFIXED AXIAL PISTON PUMP CHARACTERISTICS

Typical displacements to 500 cm3/rTypical displacements to 500 cm3/r500 cm /r500 cm /r


l i l blil i l bliMultiple assemblies possibleMultiple assemblies possible

High overall efficiencyHigh overall efficiencyHigh overall efficiencyHigh overall efficiency

Compact package.Compact package.1/2/2010 Satya Narayan Shah 66

FIXED DISPLACEMENT PISTON PUMPFIXED DISPLACEMENT PISTON PUMP

QQQQ

Q = (No. of Pistons) x (Piston Size) x (Piston Stroke) x (Drive Speed)Q = (No. of Pistons) x (Piston Size) x (Piston Stroke) x (Drive Speed)1/2/2010 Satya Narayan Shah 67

VARIABLE DISPLACEMENT PUMP - MAX FLOWVARIABLE DISPLACEMENT PUMP - MAX FLOW

STROKESTROKE

QQQQ


VARIABLE DISPLACEMENT PUMP - REDUCED FLOWVARIABLE DISPLACEMENT PUMP - REDUCED FLOW

STROKESTROKE

QQQQ


VARIABLE DISPLACEMENT PUMP - REDUCED FLOWVARIABLE DISPLACEMENT PUMP - REDUCED FLOW

STROKESTROKE

QQQQ


VARIABLE DISPLACEMENT PUMP - ZERO FLOWVARIABLE DISPLACEMENT PUMP - ZERO FLOW

STROKESTROKE

QQQQ


VARIABLE DISPLACEMENT PUMP - ZERO FLOWVARIABLE DISPLACEMENT PUMP - ZERO FLOW

STROKESTROKE


VARIABLE DISPLACEMENT PUMP - REVERSED FLOWVARIABLE DISPLACEMENT PUMP - REVERSED FLOW

QQ


VARIABLE DISPLACEMENT AXIAL PISTONVARIABLE DISPLACEMENT AXIAL PISTON


FIXED AXIAL PISTON PUMP CHARACTERISTICSFIXED AXIAL PISTON PUMP CHARACTERISTICS

Typical displacements to 500 cm3/rTypical displacements to 500 cm3/r500 cm /r500 cm /r


l i l blil i l bliMultiple assemblies possibleMultiple assemblies possible

High overall efficiencyHigh overall efficiencyHigh overall efficiencyHigh overall efficiency

Compact package.Compact package.1/2/2010 Satya Narayan Shah 75

Bent axis axial piston pumpsBent axis axial piston pumpsThe swash plate does not turn but it can be tilted The swash plate does not turn but it can be tilted back and forth. Th l f th h l t t l th di t The angle of the swash plate controls the distance that the pistons can move back and forth in their b bores. The greater the angle, the farther the pistons travel and the more oil that is displaced by the pump.p p



Radial piston pumpIn a radial piston pump, the cylinder block rotates inside a circular rotor. As the block rotates centrifugal force charging pressure or As the block rotates, centrifugal force, charging pressure, or mechanical action causes the piston to follow the inner surface of the ring, which is offset from the centreline of the cylinder block.g, yThe pistons takes in fluid as they move outward and discharge it as they move in.Displacements to 750+ cm3/rPressure capabilities to 350/400 barHigh noise levelSensitive to poor inlet conditions & contamination

h ll ffHigh overall efficiencyGood life expectancyL b lk iLarge, bulky unitsGood fluid compatibilityHi h tHigh cost.


Piston pumps ‐ introductionPiston pumps ‐ introduction


VARIABLE DISPLACEMENT RADIAL PISTON PUMPVARIABLE DISPLACEMENT RADIAL PISTON PUMP



CYLINDERSPiston‐Type Cylinders‐give straight move‐ment.

SINGLE‐ACTING CYLINDERS ‐ give force only one way SINGLE ACTING CYLINDERS give force only one way. Pressure oil is admitted to only one end of the cylinder, raising the load. An out‐side force such as gravity or a raising the load. An out side force such as gravity or a spring must return the cylinder to its starting point.DOUBLE‐ACTING CYLINDERS ‐ give force in both DOUBLE ACTING CYLINDERS give force in both directions. Pressure oil is admitted first at one end of the cylinder, then at the other, giving two‐way power.cylinder, then at the other, giving two way power.

Vane‐Type Cylinders‐give rotary movementd b l h h f d lIn a round barrel, the shaft and vane rotate as pressure oil

enters. Oil is discharged through the outlet hole in the h id f h li d other side of the cylinder.













Hydraulic accumulatorsyHydraulic accumulators are used for:Storing energyAbsorbing shockAbsorbing shockBuilding pressure regularlyg p g yMaintaining constant pressureTypes of hydraulic accumulators:Gas loaded accumulatorGas loaded accumulatorWeight loaded accumulatorSpring loaded accumulator


Types Hydraulic Accumulatorsyp y

Gas loaded accumulatorsWeight loaded accumulators Spring loaded accumulators


Characteristics of hydraulic accumulatorsyWeight loaded accumulatorConstant pressure is obtained

S i l d d lSpring loaded accumulatorCan be mounted in any positionCan be mounted in any position

Gas loaded accumulatorsGas loaded accumulatorsthe selection and use of this accumulator depends upon the

d l d f h pressure and volume needs of the systemsystem


PNEUMATIC ACCUMULATORSPNEUMATIC ACCUMULATORSUses inert gases like dry Nitrogeng y gOil and gas chambers are separated by

bl dd d hpiston, bladder or diaphragmGas is compressed while excess oil is taken Gas is compressed while excess oil is taken during off load period and expands when supplying oil to the systemFailure of packing seal causes mixing of gas Failure of packing seal causes mixing of gas and oil

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Precautions for Pneumatic AccumulatorsNEVER FILL AN ACCUMULATOR WITH OXYGEN!An explosion could result if oil and oxygen mix under pressure.p yg pNever fill an accumulator with air. When air is compressed, water vapor in the air condenses and can cause rust. This in turn ma damage seals and r in the acc m lator Also once air leaksmay damage seals and ruin the accumulator. Also, once air leaks into the oil, the oil becomes oxidized and breaks down.Always fill an accumulator with an inert gas such as dryAlways fill an accumulator with an inert gas such as dry nitrogen. This gas is free of both water vapor and oxygen; this makes it harmless to parts and safe to use.Never charge an accumulator to a pressure more than that recommended by the manufacturer. Read the label and observe the "working pressure "the working pressure.Before removing an accumulator from a hydrau-lic system, release all hydraulic pressure.y pBefore you disassemble an accumulator, release both gas and hydraulic pressures.

h di bl l k h di dWhen you disassemble an accumulator, make sure that dirt and abrasive material does not enter any of the openings1/2/2010 99Satya Narayan Shah

SPRING-LOADED ACCUMULATORSSPRING LOADED ACCUMULATORSIn operation, pressure oil loads the piston by compressing the spring When pressure drops thecompressing the spring .When pressure drops, the spring forces oil into the system.The accumulator can be used as a gradual pressureThe accumulator can be used as a gradual pressure builder for an automatic transmission. When the transmission is shifted pressure drops and thetransmission is shifted, pressure drops and the accumulator sends a "surge" of oil in to "take up slack " This fills the chamber behind the clutchslack." This fills the chamber behind the clutch pistons. Then pressure builds gradually for a smooth engagement of the clutchengagement of the clutch.By controlling the flow of oil to the accumulator, the time needed to charge it can also be controlled


SPRING-LOADED ACCUMULATORSSPRING LOADED ACCUMULATORSThe operation of spring‐loaded accumulators can be

i d b h i ) h h f h i ) h varied by changing 1) the strength of the spring, 2) the length of the spring, 3) the preload on the spring, 4)

)the size of the piston or, 5) the length of the piston stroke.



Hydraulic ValvesyHydraulic valves regulateHydraulic valves regulate

PressureDirectionVolume

T f lTypes of valvePressure control valvesPressure control valvesDirectional control valvesVolume control valves


Pressure Control Valves (PCV) ( )PCV are used to limit or reduce system pressureUnload a pumpSet the pressure

Examples of PCV areRelief valves

d lPressure reducing valvesP l Pressure sequence valves etc


Relief ValvesRelief ValvesUsed as safety valvesPrevents the increase of system pressure f h ifi d from the specified pressure rangeCracking pressure is the pressure at hich Cracking pressure is the pressure at which the relief valves first begin to opene e e a es s beg o opeFull flow pressure is the pressure at which the valve passes its full quantity of oil


Pressure Reducing ValvesTo keep the pressure in one branch of circuit below than that of main circuitWh t ti thi l i When not operating this valve is openThe spring tension can be adjusted using The spring tension can be adjusted using screwThis valve will limit maximum pressure in the secondary circuit irrespective of pressure changes in the main circuitpressure changes in the main circuit


Pressure sequence ValvesTo control the sequence of flow to various b h f i itbranches of circuitValves allow flow to a second function Valves allow flow to a second function only after a first has been fully satisfiedWhen closed, the valve directs oil freely to the primary circuitto the primary circuitWhen opened, the valve diverts oil to a p ,secondary circuith d li d b i i k The second cylinder begins its stroke

once first completes its strokeonce first completes its stroke1/2/2010 107Satya Narayan Shah

Directional control valvesDirects the flow of oil in hydraulic system

TypesTypesCheck valvesCheck valvesSpool valves

Check valves:‐o One way valveo Open to allow flow in one direction but close to pprevent flow in the opposite direction

o Mostly used to stop reverse flowo Mostly used to stop reverse flow1/2/2010 108Satya Narayan Shah

Spool Directional valvepDirects oil to start, operate and stop the actuating units on modern h d li hydraulic systemS l l b t i d b it Spool valve can be categorized by its position and way of directing the oil position and way of directing the oil lineFor example three position and four p pway valve


Spool Directional valvep


Spool Directional valveSpool Directional valve


Spool Directional valvep


Volume control valvesControls the volume or flow of oil usually by throttling or divertingSpeed of cylinder or motor is

l t d b thi lregulated by this valveMostl used in fi ed displacement Mostly used in fixed displacement type of valve type of valve
















Hydraulic filterFilters the contamination from the oilIt can be taken from the machine and l d d i i i i d If cleaned during servicing period. If clogged bypass valve comes in actionclogged bypass valve comes in actionIs generally cartridge types ge e a y ca dge ypeHydraulic filter generally is in between y g yreturn line and tank






Hydraulic hosesHydraulic hosesCarries hydraulic oil from one ycomponent to the another in hydraulic systemsystemAre of high pressure and low as per the il fl lioil flow line

Flexible in natureFlexible in natureCan be connected with another pipe h h lithrough couplingSometimes steel pipes can be used for Sometimes steel pipes can be used for connecting two components if they are closed to otherclosed to other


Hydraulic hoses






Hydraulic fluidThe hydraulic fluid is the transmitting medium of the

hydraulic system It performs various tasks:hydraulic system. It performs various tasks:Transmission of hydraulic energyPrevention of corrosion of moving internal partsRemoval of dirt, abrasive matter, etcDissipation of heatLubricationLubricationSealing


Hydraulic fluid requirementsMust not boil, vaporize or freeze within the temperature limits of the systemp yMust not corrode the internal partsVi it t i t blViscosity must remain stableMust be chemically stableCapable of resisting foamingCapable of separating from waterCapable of separating from waterCompatible with seals and gasketsLubricating abilityOxidation resistanceLoad carrying capacity


Too high a viscosity increases friction, resulting in :Too high a viscosity increases friction, resulting in :High resistance to flow.Increased power consumption due to frictional lossIncreased power consumption due to frictional loss.High temperature caused by friction.Increased pressure drop because of the resistance.Increased pressure drop because of the resistance.Possibility of sluggish or slow operation.Difficulty in separating air from oil in reservoir.y p gGreater vacuum at the pump inlet, causing cavitation.Higher system noise level.g y

And should the viscosity be too low :I t l l k iInternal leakage increases.Excessive wear.Pump efficiency may decrease causing slower operation of the actuatorPump efficiency may decrease, causing slower operation of the actuator.Increased temperature result from leakage losses


Types of hydraulic fluidsTypes of hydraulic fluidsPetroleum oilPetroleum oilFire resistant fluidsFire resistant fluids• Water glycols• Water glycols• Water‐oil emulsionWater oil emulsionSynthetic oilSynthetic oil


Typical hydraulic circuit yp y. Control valve

Pressure ReliefValveL.H. Cylinder R.H. CylinderValveL.H. Cylinder

Main pumpHydraulic filter

Tank



Design of a simple hydraulic systemDesign of a simple hydraulic systemWhen designing a simple hydraulic system, we When designing a simple hydraulic system, we need to calculate the following:Pressure force and areaPressure, force and areaSpeed of an actuatorFlow velocity in pipesPipe size requirementsPipe size requirementsWork, horsepower and torqueR i i iReservoir sizing


Pressure indicates work loadResistance of a load generates pressure. Pressure equals to the force of the load divided Pressure equals to the force of the load divided by the piston area. We can express this relationship by the general formula:P = pressure; f = force and a = area

FAF P =A


Force is proportional to pressureForce is proportional to pressure and areaand area

When a hydraulic cylinder is used to clamp orWhen a hydraulic cylinder is used to clamp orpress, its output force can be computed as follows:

F = p x a


Computing piston areaThe area of a piston can be computed by thisformulaformula

π 2dxA π= dx

4A=

4


Speed of an actuatorHow fast a piston travels or a motor rotates depends on its size and the rate of oil flow into it depends on its size and the rate of oil flow into it. To relate flow rate to speed, consider the volume h b fill d i h i that must be filled in the actuator to cause a given amount of travel.

x AreaSpeedVolume x AreaSpeedTimeVolume =

TimeVolume

Speed =Area

Speed =


Velocity in pipesVelocity in pipesThe velocity at which the hydraulic fluid flows The velocity at which the hydraulic fluid flows through the lines is an important design consideration because of the effect of velocity on consideration because of the effect of velocity on friction.Generally the recommended velocity ranges are:Generally the recommended velocity ranges are:• Pump inlet line = 0.61 – 1.22 metres per second• Working lines = 2.13 – 6.10 metres per second


Pipe size requirementsIf the LPM and desired velocity are known, use this relationship to find the cross sectional area:this relationship to find the cross‐sectional area:

16667xLPMsecond)permm(inVelocity

16667 x LPM )(mm Area 2 =second)per mm (inVelocity


Pipe size requirementsWhen the LPM and size of pipe is given, use thisformula to find what the velocity will be:formula to find what the velocity will be:

16667LPM)(mmArea

16667x LPM )secondper (mm Velocity 2=

Alternatively, the area can be obtained from theselection chart

)(mmArea

selection chart.


Pipe size requirementsSelect the proper conductor internal conductor internal diameter if the flow rate is knownrate is known.

Determine exactly what ythe velocity will be if the conductor size and flow rate are known.


Work and powerWork and powerWhen a force is exerted through a distance, work When a force is exerted through a distance, work is done.

Work = force x distance

Work is usually expressed in joules. Work is usually expressed in joules. For example, if a 50n weight is lifted 3m, the work done is 150nm or jdone is 150nm or j.


Work and powerThe previous formula does not take into consideration how fast the work is done. consideration how fast the work is done. The rate of doing work is called power.

WorkorDistance x ForcePower=Time

or Time

Power

The usual unit of power is the horsepower (watt), abbreviated hp (w). (1 hp = 746 watts)( ), p ( ) ( p 74 )One watt is equivalent to 1 newton lifted one metre in one second)metre in one second)


Horsepower in a hydraulic systemIn the hydraulic system, speed and distance are indicated by the LPM flow and force is indicated indicated by the LPM flow and force is indicated by pressure. Th i ht h d li thi Thus, we might express hydraulic power this way:

MetresSquareNewtons x

MinutesLitres Power =

q


Horsepower in a hydraulic systemBy changing the units, we get

barxLPM600

barx LPM kW =600


Horsepower in a hydraulic systemThese horsepower formulas tell the exact power being used in the system being used in the system. The horsepower required to drive the pump will b h t hi h th thi i th t i be somewhat higher than this since the system is not 100% efficient. The formula is changed when the average efficiency (η) is taken into account.y

barxLPMηx 600

bar x LPMkW =η


Horsepower and torqueHorsepower and torqueThe following are general torque‐power formulasThe following are general torque power formulasfor any rotating equipment:

kW x 9550Torque =rpm

q

9550rpmx Torque kW =

9550


Margin of errorMargin of errorWhen working on the formulas, we must take into When working on the formulas, we must take into consideration the margin of error if it is given.

Working pressure, p = operating pressure –i f margin of error


Reservoir sizingReservoir sizingFor industrial use, a general sizing rule is used:For industrial use, a general sizing rule is used:

T k i (li ) l Tank size (litres) = pump lpm x 3


Given the following:Given the following:• Load = 35 000NDistance 0 5m• Distance = 0.5m

• Operating pressure = 60 bar• Margin of error = 10%• Rate of raising load = 0.15 m/sec• Flow velocity = 2.5 m/sec• System efficiency = 90%System efficiency = 90%


A f i tArea of pistonLoad is 35000 NPressure is 60 bar

25 m0.0065000 35ForceArea === 5 m0.0065

10x 54Pressure Area


Velocity

Rate at which load is to be raised Rate at which load is to be raised = 15 cm/sec = 0.15m/sec 15 cm/sec 0.15m/secWhich is equal to 9 m/minq 9 /


R t f il flRate of oil flowR t f il fl t l t Rate of oil flow = travel rate x area

= 9 x 0.00659 x 0.0065= 0.0585 m3/min= 0.0585 x 1000

litres/minlitres/min= 58.5 litres/min5 5 /


Wattage of motor

barxLPMx600barx LPM kW =η6058 5

x 600 η

6.5kW60x 58.5kW == 6.5kW 0.9x 600

kW


I id di t f iInside diameter of pipeTo determine the inside diameter of the pipe if a To determine the inside diameter of the pipe if a flow velocity of 2.5 m/sec is to be maintained. U i th f 6 LPM d / Using the nomogram, for 6.5 LPM and 2.5 m/sec, we get:Area of fluid conductor = 4 cm2


Diameter of hydraulic hoseWith the area of fluid conductor being 4 cm2The diameter of the hydraulic hose can be obtained:y

4 d x 4

2 =π

4x44

4x 4 d =π

cm 2.26 d =


Reservoir sizingReservoir size

Reservoir size = 58.5 x 3

= 175.5 litres


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Hydraulics IOE PPT