graham spencer festo didactic12.09.20151 basic principles of hydraulics symbols page 19

Graham Spencer Festo Didactic

19.04.23 1

Basic Principles of Hydraulics

Symbols

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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)

1


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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 Way

4/2 way valve

Changeover

A

P

A

P T

A B

P TPage 24


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Valve Description Number of

Ports3

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Number of Control positions

Number of Ports

3

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Valve Description


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(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)


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)


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)


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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Pressure Relief Valve Remote pilot control

with internal drain

Internally piloted or 2 stage relief valve

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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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Pressure regulator with reverse flow by-pass built in

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A

B


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


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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 ControlsPressure 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.

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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


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SymbolsMiscellaneous

Reservoirs

Vented to atmosphere

Return line below fluid level

Return line above fluid level

Header tank

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Conditioning Units Filter or

Strainer

Cooler

Water cooled

Heater

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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 = F A 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/s Flow 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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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/secondPage 38


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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)

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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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graham spencer festo didactic12.09.20151 basic principles of hydraulics symbols page 19

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