1. Fluid Power Control

2. Module:03 ~ Hydraulic SYSTEM COMPONENTS
FLUID POWER
Module:03 ~ Hydraulic SYSTEM COMPONENTS
Sources of Hydraulic Power
Construction and working of pumps – Variable displacement pumps
Actuators:
Hydraulic cylinders, performing linear motion
Hydraulic motors, performing continuous rotary motion
Hydraulic rotary actuators, performing limited angular
Control Components:
Pressure Control Valve
Direction control valve
Flow control valves

3. Pressure Control Valves
control components
FLUID POWER
Pressure Control Valves
What is a PCV?

4. Pressure Control Valves
control components
FLUID POWER
Pressure Control Valves
Why do we need a PCV in hydraulic circuit?
Limiting maximum system pressure at a safe level.
Regulating/reducing pressure in certain portions of the circuit.
Unloading system pressure.
Assisting sequential operation of actuators in a circuit with pressure control.
Reducing or stepping down pressure levels from the main circuit to a lower pressure in a sub-circuit

5. Pressure Control Valves
control components
FLUID POWER
Pressure Control Valves
Types:
Pressure-relief valve.
Pressure-reducing valve.
Unloading valve
Pressure-sequence valve.

6. Pressure-Relief Valve
FLUID POWER
control components - PCV
Pressure-Relief Valve
What is a Pressure Relief Valve for?
Comparison with a fuse in an electrical system.
Construction and Working Principle.

7. Pressure-Relief Valve
control components - PCV
FLUID POWER
Pressure-Relief Valve
Spool (1), Housing (2), Spring (3), Spring seat (4), & Adjusting knob (5).
max

8. Pressure-Relief Valve
control components - PCV
FLUID POWER
Pressure-Relief Valve
SUMMERY:
The pressure at which the valve begins to open is known as cracking pressure
The pressure that exists at full pump flow can be substantially greater than cracking pressure.
It is the maximum pressure level permitted by the relief valve.
Spring stiffness determines the difference between full pump flow pressure and cracking pressure.

9. Pressure-Relief Valve
control components - PCV
FLUID POWER
Pressure-Relief Valve
Points to note:
It limits the maximum pressure in a hydraulic circuit by keeping it below a preset level.
It provides protection against any overloads; or it limits the force or torque produced by hydraulic cylinders or motors.
It can bypass fluid anytime, or all the time, without intervention by maintenance.
A well-designed circuit never bypasses fluid unless there is a malfunction. This eliminates most overheating problems and saves energy.
Note the external adjusting screw varies spring force and, thus, the pressure at which the valve begins to open (cracking pressure) also varies.

10. Pressure-Relief Valve
control components - PCV
FLUID POWER
Pressure-Relief Valve
Graphical Symbol

11. Pressure-Relief Valve
control components - PCV
FLUID POWER
Pressure-Relief Valve
Symbolic Representation of Partial Hydraulic Circuit
Typical Hydraulic Power Pack

12. Pressure-Relief Valve
control components - PCV
FLUID POWER
Pressure-Relief Valve
A relief valve is not needed if a pressure-compensated vane pump is used.

13. FLUID POWER
control components - PCV
Pressure-Relief Valve
A pressure-relief valve has a pressure setting of 140 bar. Compute the power loss (kW) across this valve if it returns all the flow, m3/s, back to the tank from a pump.
50 bar
100 bar

14. Pressure-Relief Valve
FLUID POWER
control components - PCV
Pressure-Relief Valve
A pressure-relief valve contains a poppet with an area of 4.2 cm2 on which the system pressure acts. During assembly, a spring with a spring constant of 3300 N/cm is installed in the valve to hold the poppet against its seat. The adjustment mechanism is then set so that the spring is initially compressed to 0.5 cm from its free-length condition. In order to pass full pump flow through the valve at the pressure-relief valve pressure setting, the poppet must move 0.30 cm from its fully closed position.
(a) Determine the cracking pressure.
(b) Determine the full pump flow pressure (pressure-relief valve pressure setting).
(c) What should be the initial compression of the spring in pressure-relief valve if the full pump flow is to be 40% greater than the cracking pressure?
50 bar
100 bar

15. A Typical Hydraulic Circuit where a pressure Reducing Valve is needed.
FLUID POWER
control components - PCV
Pressure-Reducing Valve
50 bar
A Typical Hydraulic Circuit where a pressure Reducing Valve is needed.
What is a Pressure- Reducing Valve?
Why is a Pressure- Reducing Valve used in a hydraulic system?
100 bar

16. Pressure-Reducing Valve
control components - PCV
FLUID POWER
Pressure-Reducing Valve
How does it work?
..\video\Edited\Function of a Pressure Reducing Valve in a Hydraulic System.wmv

17. Pressure-Reducing Valve
control components - PCV
FLUID POWER
Pressure-Reducing Valve
APPLICATION

18. Graphical Symbol Pressure-Reducing Valve control components - PCV
FLUID POWER
Pressure-Reducing Valve
Graphical
Symbol

19. control components - PCV
FLUID POWER
Pressure-Reducing Valve
APPLICATION
Draw a hydraulic circuit for controlling two double acting cylinders by two separate 4/3 solenoid operated spring centered closed neutral DCV. Assume actuator -2 will be operated at reduced pressure.

20. Dumps excess fluid with little or no pressure.
control components - PCV
FLUID POWER
Unloading Valve
Normally closed type
Dumps excess fluid with little or no pressure.
It unloads the pump.

21. Application of unloading valve
control components - PCV
FLUID POWER
Application of unloading valve
in a punching press

22. Application of unloading valve in a punching press
control components - PCV
FLUID POWER
Unloading Valve
Application of unloading valve in a punching press
(High-Low circuit)

23. control components - PCV
FLUID POWER
Unloading Valve

24. control components - PCV
FLUID POWER

25. Operation of UNLOADING VALVE control components - PCV FLUID POWER
TANK PORT
PILOT PORT
PUMP PORT

26. UNLOADING VALVE With as an Integral Part control components - PCV
FLUID POWER
UNLOADING VALVE
With
CHECK VALVE
as an Integral Part

27. ** APPLICATION OF UNLOADING VALVE **
control components - PCV
FLUID POWER
** APPLICATION OF UNLOADING VALVE **

28. control components - PCV
FLUID POWER

29. ** APPLICATION OF UNLOADING VALVE **
control components - PCV
FLUID POWER
** APPLICATION OF UNLOADING VALVE **

30. Unloading Valve ¬ Points to note:
control components - PCV
FLUID POWER
Unloading Valve ¬ Points to note:
It allows rapid discharge of pressurized oil near atmospheric pressure.
These valves are very reliable and seldom require maintenance, adjustment or replacement.
An unloading valve requires no electric signals. This eliminates the need for maintenance.
An unloading valve is used to perform operations such as stamping, coining, punching, piercing, etc.

31. Application Sequential Valve:
control components - PCV
FLUID POWER
Sequential Valve:
Application
A machining operation where the work-piece must be clamped with a certain force before the cutting tool starts moving to make contact with the work-piece.

32. control components - PCV
FLUID POWER
Sequential Valve: B B P A P A A

33. control components - PCV
FLUID POWER
Sequential Valve: B P A

34. control components - PCV
FLUID POWER
Sequential Valve: B P A P

35. control components - PCV
FLUID POWER B P A P
Sequential Valve

36. Application Sequential Valve:
FLUID POWER
control components - PCV
Sequential Valve:
Application
The Hydraulic Circuit for a clamp cylinder to extend first to hold a work-piece and then a second cylinder to extend to bend the work-piece in the desired shape.

37. control components - PCV
FLUID POWER
Sequential Valve:
Application