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Graham Spencer Festo Didactic 02.02.2010 1
Basic Principles of Hydraulics
Symbols
Page 19
شركت مهندسي رانش هيدروليك سهند طراحي و ساخت سيستمهاي هيدروليك
تبريز –ايران 09144142432: تلفن همراه
0411-3802509: فكس
Graham Spencer Festo Didactic 02.02.2010 2
Symbols
Fixed Displacement One direction of flow. Constant delivery for constant speed
Variable Displacement One direction of flow. Variable delivery for constant speed
Directional of flow reversible. Variable delivery for constant speed.
Pumps
Pressure compensated variable pumpOne direction of flow, adjustable spring and pump case drain.Method of adjustment is shown on the arrow
Hydraulic Energy Source(simplified representation)Page 21
Graham Spencer Festo Didactic 02.02.2010 3
Symbols
Motors
Fixed Displacement
Variable Displacement
One direction of rotation. Constant shaft speed for constant flow rate
Either direction of rotation, depending on direction of flow. Constant shaft speed for constant flow rate.
Either direction of rotation. Speed variable for constant flow.
Electric Motor
Engine
M
M
Drive units
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Symbols
Semi rotary actuator Limited rotary movement eg
1800
x y
Equipment to transform a pressure x in to a pressure y
Single acting
Continuous
Pressure Intensifiers
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Actuators
Symbols
Single Acting Returned by external force
Spring return
Vent
Telescopic Cylinder
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Actuators
Symbols
Double acting Double ended piston rod
Cushioned Variable cushioning at both ends.
Double acting Forward and return stroke under powerSingle piston rod.
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Directional Control Valves
Symbols
Porting(2 position)
Two Way2/2 way valve
Normally closed
Three Way
3/2 way valve
Normally closed
Four Way4/2 way valve
Changeover
A
P
A
P T
A B
P TPage 24
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Valve DescriptionNumber of Ports 3
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Number of Control positions
Number of Ports 3
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Valve Description
Graham Spencer Festo Didactic 02.02.2010 10
(Number of Boxes)
2Number of Control positions
Number of Ports 3
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Valve Description
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Method of Operation
Push Button
(Number of Boxes)
2Number of Control positions
Number of Ports 3
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Valve Description
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Method of Return
Spring
Method of Operation
Push Button
(Number of Boxes)
2Number of Control positions
Number of Ports 3
Page 24
Valve Description
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Method of Return
Spring
Method of Operation
Push Button
(Number of Boxes)
2Number of Control positions
Number of Ports 3
Normally closed or Normally open
Flow path blocked when valve is at rest
Flow path open when valve is at rest
Normally Closed
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Valve Description
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SymbolsDirectional Control Valves
3 position valves
Closed centre
Open centre
Tandem centre
A B
P T
A B
P T
A B
P T
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SymbolsDirectional Control Valves
3 position valves Floating Centre
Regenerative Centre
A B
P T
A B
P T
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SymbolsMethods of Operation General manual operation
Usually used to represent a manual override
Lever operation
Foot Pedal operation
Push Button operation
Detent operationUsually used with lever operation
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SymbolsMethods of Operation
Roller operation
Spring operationUsually used as a return or centring function
Solenoid operation
Internal pilot or 2 stage operationUsually used with solenoid operation
Pilot operation
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SymbolsNon return valves
FreeOpens if inlet pressure is higher than outlet pressure
Spring loaded Opens if inlet pressure is higher than outlet pressure plus spring load
Pilot operated Can be opened to permit reverse flow by means of pilot pressure
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SymbolsPressure Controls
Pressure Relief Valve
Single stage with internal drain
With external drain
Also sometimes represented so
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SymbolsPressure Controls
Pressure Relief Valve Remote pilot control with
internal drain
Internally piloted or 2 stage relief valve
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SymbolsPressure Controls
Pressure Regulating Valves
Downstream pressure control Forward flow only external drain
A
B
3 way pressure regulating valve
Downstream pressure control.If outlet pressure exceeds set pressure, flow is diverted to tank.
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SymbolsPressure Controls
Pressure regulator with reverse flow by-pass built in
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A
B
SymbolsPressure Controls
Pressure Relief Pressure Regulator
Shown normally closed
Shown normally open
Pressure operation from inlet
Pressure operation from outlet
Valve is closed until the pressure at the inlet is high enough to open it (set pressure). Flow is then usually to tank.
Valve is open until the pressure at the outlet is high enough to close it (set pressure). Flow is usually to cylinder or other part of the circuit.
Comparison
Graham Spencer Festo Didactic 02.02.2010 25
SymbolsPressure Controls
Sequence Valves Maintains upstream pressure, allows flow through to other functions.
Two stage sequence valve
Maintains upstream pressure, allows flow through to other functions.External drain
Counterbalance valve
Provides controlled backpressure for load support.With built in by-pass
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SymbolsFlow Controls
Non pressure compensated
Flow proportional to preset area times the square root of the pressure drop across restrictor
Flow restricted in one direction only.
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SymbolsFlow Controls
Pressure Compensated
Flow proportional to preset area irrespective of valve pressure drop. Direction of flow as indicated (non reversible). Excess flow must find alternative path.
Pressure & Temperature Compensated
Preset area automatically adjusts to compensate for viscosity changes
Bypass Regulator Excess flow bypassed internally
Also sometimes
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SymbolsFlow Controls
Flow dividerInput flow is divided to 2 flows of fixed ratioPressure compensated.
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SymbolsProportional Valves Valve with 2 distinct operating positions,
fully open and fully closed, and an infinite number of intermediate positions.
4/3 directional control valve, proportional.3 distinct operating positions with closed centre position and an infinite number of intermediate positions.Solenoid current is controlled through proportional amplifier.
Servo valveControlled by a torque motor.Direction of movement is dependent on voltage polarity.Amount of movement is dependent on magnitude of current.Page 32
Graham Spencer Festo Didactic 02.02.2010 30
SymbolsModulating Control Valves
More often referred to as Proportional Control Valves and usually solenoid operated.
With these valves there is a known relationship between the position of the spool and the flow through the valve. Therefore flow (speed) can be controlled electronically without the need for adjusting manual valves.
Spool Travel
FlowRate
Full flow
Proportional Valve
Conventional valve
Graham Spencer Festo Didactic 02.02.2010 31
SymbolsMiscellaneous
Reservoirs Vented to atmosphere
Return line below fluid level
Return line above fluid level
Header tank
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SymbolsMiscellaneous
Conditioning UnitsFilter or Strainer
Cooler
Water cooled
Heater
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SymbolsMiscellaneous
Shut off valve
Accumulator
Gas type
Pressure Gauge
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Hydraulic Formulae
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Force (F) = Area (A) x Pressure (P)Newtons (N) Square metres (sq. m) Pascals (Pa)Pounds (lbf) Square inches (sq. in) Pounds/sq.in (psi)
Note:* The pascal is a very small unit of pressure.
100 Kpa= 10N = 14.5 psi = 1 Barcm2
e.g. 5000KPa = 50 Bar = 725 psi
F = A x P P = F A = FA P
-------------------------------------
Hydraulic Formula
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Flow Rate = Flow Velocity x Flow areametres 3 / sec metres / second metres 2
Usually flow rate is given in Litres/minute and flow area given in cm2 or mm2 . Care must be taken to ensure the correct multiples are used.Eg. Calculate the cross sectional area required for the suction line of a pump delivering 40 l/min with a maximum flow velocity of 1.2 m/s.
Area = Flow rate 40 l/min = 40/60 x 10-3 m3/sFlow velocity
Area = 40 x 10 -3 m2
60 x 1.2
Area = 0.555 x 10 -3 m2 (Pipe bore of 26.6mm)--------------------------------------------------------------------------
Volume of cylinder (base end) = Piston area x stroke length
Volume of cylinder (rod end) = (Piston area - Rod area) x stroke length
Hydraulic Formula
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Graham Spencer Festo Didactic 02.02.2010 37
Hydraulic Formula
Work done = Force x distance moved
Force on a piston = Pressure x area of pistonSo, work done = Pressure x area x distance moved
Area x distance moved= Volume
SoWork done = Pressure x volume
Power is the rate of doing work or, work done per unit of time.
Volume per unit time is flow rate - m3/second
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Graham Spencer Festo Didactic 02.02.2010 38
Hydraulic Formula
SoHydraulic power = Pressure x Flow rate
If pressure is in Pascals (N/m2) and the flow rate is in m3/second then
Hydraulic power = Pressure x Flow rate - (Nm/s) = Watts
It is usual to give flow rate in litres/minute and pressure in bars. To use these units in the calculation the following conversion has to be made.
Hydraulic Power (kW) = Pressure (bar) x Flow rate (l/min)
600
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Bar x 100,000 x Flow rate (L/min) = Power in kilowatts60,000,000
To calculate power in Watts the following formula can be used
Pressure x Flow rate = Power
N x m3 = Nm = Wattsm2 sec sec
To use more useful units.
Bar times 100,000 = N/m2 L/min divided by 1000 then divided by 60 = m3/sec
So Bar x 100,000 x Flow rate (L/min) = Power in Watts60,000
Pressure (Bar) x Flow rate (L/min) = Power in kW600
Graham Spencer Festo Didactic 02.02.2010 40
1) If a system pressure of 3000 p.s.i acts on a piston area of 3 sq ins, (approx 2 ins diameter) what force will be produced?
2) If a force of 10,000 lb is produced from a cylinder with a piston area of 2.5 sq ins, what is the pressure build up in the system?
3) If a force of 15,000 Newtons is produced in a cylinder with a piston area of 20 sq cm, what is the pressure build up in the system?
4) A cylinder with piston area 150 sq cm and stroke length of 400cm must fully extend in 15 seconds. What flow rate (in Litres/min) must the pump deliver to achieve this?
5) If a hydraulic pump is delivering a flow of 40 litres / min against a pressure of 150 bar, what is the power consumption (in KW) at the pump?
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Method of Return
Method of Operation
(Number of Boxes)
Number of Control positions
Number of Ports
Normally closed
or Normally open
Graham Spencer Festo Didactic 02.02.2010 44
x y
Graham Spencer Festo Didactic 02.02.2010 45
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A1 A2 A3
B1 B2 B3
P T
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A1
A2
A3
B1
B2
B3
P T
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A1 A2 A3
B1 B2 B3
P T
Graham Spencer Festo Didactic 02.02.2010 49
A1 A2 A3
B1 B2 B3
P T
Graham Spencer Festo Didactic 02.02.2010 50
A1 A2 A3
B1 B2
P T
Graham Spencer Festo Didactic 02.02.2010 51
A1 A2 A3
B1 B2
P T
شركت مهندسي رانش هيدروليك سهند طراحي و ساخت سيستمهاي هيدروليك
تبريز –ايران 09144142432: تلفن همراه
0411-3802509: فكس
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