1. Basic principles of hydraulic symbols

2. Symbols
Pumps
One direction of flow. Constant delivery for constant speed
Fixed Displacement
Variable Displacement
One direction of flow. Variable delivery for constant speed
Pressure compensated variable pump
One direction of flow, adjustable spring and pump case drain.
Method of adjustment is shown on the arrow
Directional of flow reversible. Variable delivery for constant speed.
Hydraulic Energy Source
(simplified representation)

3. Symbols Drive units M Electric Motor M Engine Motors
One direction of rotation. Constant shaft speed for constant flow rate
Fixed Displacement
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.
Variable Displacement

4. Pressure Intensifiers
Symbols
Semi rotary actuator
Limited rotary movement eg 1800
Pressure Intensifiers
Equipment to transform a pressure x in to a pressure y
Single acting
x y
Continuous

5. Symbols Actuators Single Acting Returned by external force
Spring return
Vent
Telescopic Cylinder

6. Symbols Actuators Forward and return stroke under power Double acting
Single piston rod.
Double acting
Double ended piston rod
Cushioned
Variable cushioning at both ends.

7. Symbols Directional Control Valves A P 2/2 way valve Two Way
Normally closed
Two Way
Porting
(2 position) A
P T
3/2 way valve
Normally closed
Three Way
A B
P T
4/2 way valve
Changeover
Four Way

8. Valve description 3
Number of Ports

9. Valve description 3
Number of Ports
Number of Control positions

10. 3 2 Valve description Number of Ports Number of Control positions
(Number of Boxes)

11. 3 2 Push Button Valve description Number of Ports
Number of Control positions 2
(Number of Boxes)
Push Button
Method of Operation

12. 3 2 Push Button Spring Valve description Number of Ports
Number of Control positions 2
(Number of Boxes)
Push Button
Method of Operation
Method of Return
Spring

13. 3 2 Push Button Spring Normally Closed Valve description
Number of Ports 3
Number of Control positions 2
(Number of Boxes)
Push Button
Method of Operation
Flow path blocked when valve is at rest
Method of Return
Spring
Normally Closed
Normally closed
Flow path open when valve is at rest
or Normally open

14. Symbols Directional Control Valves Closed centre 3 position valves
Open centre A B P T
Tandem centre

15. Symbols Directional Control Valves 3 position valves Floating Centre
Regenerative Centre

16. Symbols Methods of Operation General manual operation
Usually used to represent a manual override
Lever operation
Foot Pedal operation
Push Button operation
Detent operation
Usually used with lever operation

17. Symbols Methods of Operation Pilot operation Roller operation
Spring operation
Usually used as a return or centring function
Solenoid operation
Internal pilot or 2 stage operation
Usually used with solenoid operation

18. Symbols Non return valves
Opens if inlet pressure is higher than outlet pressure
Free
Spring loaded
Opens if inlet pressure is higher than outlet pressure plus spring load
Pilot operated

19. Symbols Pressure Controls Single stage with internal drain
Pressure Relief Valve
Also sometimes represented so
With external drain

20. Symbols Pressure Controls Pressure Relief Valve
Remote pilot control with internal drain
Internally piloted or 2 stage relief valve

21. Symbols Pressure Controls A Pressure Regulating Valves
Downstream pressure control Forward flow only external drain B
Downstream pressure control.
If outlet pressure exceeds set pressure, flow is diverted to tank.
3 way pressure regulating valve

22. Symbols Pressure Controls
Pressure regulator with reverse flow by-pass built in

23. Symbols Pressure Controls - comparison
Pressure Relief Pressure Regulator
Pressure operation from inlet A B
Pressure operation from outlet
Shown normally closed
Shown normally open
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.

24. Symbols Pressure Controls
Maintains upstream pressure, allows flow through to other functions.
Sequence Valves
Maintains upstream pressure, allows flow through to other functions.
External drain
Two stage sequence valve
Provides controlled backpressure for load support.
With built in by-pass
Counterbalance valve

25. Symbols Flow 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.

26. Symbols
Flow Controls
Flow proportional to preset area irrespective of valve pressure drop. Direction of flow as indicated (non reversible). Excess flow must find alternative path.
Pressure Compensated
Also sometimes
Pressure & Temperature Compensated
Preset area automatically adjusts to compensate for viscosity changes
Bypass Regulator
Excess flow bypassed internally

27. Symbols Flow Controls Input flow is divided to 2 flows of fixed ratio
Pressure compensated.
Flow divider

28. Symbols Proportional 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 valve
Controlled by a torque motor.
Direction of movement is dependent on voltage polarity.
Amount of movement is dependent on magnitude of current.

29. Symbols Modulating 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
Flow
Rate
Full flow
Proportional Valve
Conventional valve

30. Symbols Miscellaneous Vented to atmosphere Reservoirs
Return line below fluid level
Return line above fluid level
Header tank

31. Symbols Miscellaneous Conditioning Units Filter or Strainer Cooler
Water cooled
Heater

32. Symbols Miscellaneous Pressure Gauge Shut off valve Accumulator
Gas type

33. Hydraulic formulae

34. Hydraulic formula 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 = Bar
cm2
e.g. 5000KPa = 50 Bar = psi
F = A x P P = F A = F
A P

35. Hydraulic Formula Flow Rate = Flow Velocity x Flow area
metres 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 m3/s Flow velocity
Area = 40 x m2
60 x 1.2
Area = x m2 (Pipe bore of 26.6mm)
Volume of cylinder (base end) = Piston diameter x stroke length
Volume of cylinder (rod end) = (Piston dia - Rod dia) x stroke

36. Hydraulic Formula Work done = Force x distance moved
Force on a piston = Pressure x area of piston
So,
work done = Pressure x area x distance moved
Area x distance moved = Volume So
Work 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

37. Hydraulic Formula So Hydraulic 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

38. Hydraulic Formula Force (F) = Area (A) x Pressure (P)
Newtons (N) Square Centimetres (sq. cm) Pascals (Pa)
Pounds (lbf) Square inches (sq. in) Pounds/sq.in (psi)
Bar
Note:
* The pascal is a very small unit of pressure.
100 Kpa = 10N = 14.5 psi = Bar
cm2
e.g. 5000KPa = 50 Bar = 725 psi
F = A x P P = F A = F
A P

39. To calculate power in Watts the following formula can be used
Pressure x Flow rate = Power
N x m3 = Nm = Watts
m2 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 Watts
60,000
Bar x 100,000 x Flow rate (L/min) = Power in kilowatts
60,000,000
Pressure (Bar) x Flow rate (L/min) = Power in kW
600

40. 1). If a system pressure of 3000 p. s
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?

41. Number of Control positions
Number of Ports
Number of Control positions
(Number of Boxes)
Method of Operation
Method of Return
Normally closed
or Normally open

42. x y