Hydraulic Valves

1. Hydraulic Valves

2. Objectives related to Valves
1. State the function of a valve.
2. Describe the three types of valves.
3. List the four uses of pressure control valves.
4. Describe two types of relief valves, and their uses.
5. State the difference in cracking pressure and full-flow pressure.
6. Describe the two main types of pressure reducing valves.
7. State the function of a pressure sequencing valve.
8. State the function of unload valves.
9. List and describe the five types of directional control valves.
10. Explain the difference in a valve stack and a unibody valve.
11. List and describe two types of volume control valves.
12. List and describe the types of flow control valves.
13. List and describe the types of flow divider valves
14. Describe the proper procedures to follow before and during valves disassembly.
15. Describe the proper procedures to follow in reassembly of valves.
16. List and describe three ways valves can be actuated/operated.
17. Identify six common valve symbols

3. Obj 1. Functions of a valve
• direct the flow of fluid
• regulate the pressure
• control volume

4. Obj. 2 Three types of valves
• Pressure – adjust psi for some purpose
• Directional -- route the fluid to the desired
actuator
• Volume Control or Flow Control -- control
the amount of flow

5. Obj 3 Uses of pressure control
valves
• Limit system pressure
• Reduce pressures
• Set pressure at which oil enters a circuit
• Unload a pump

6. Obj. 4 Types of relief valves, and
their uses
• Direct acting -- used with low volume and
infrequent use
• Pilot operated -- used with high volume
with little pressure difference

7. Obj 5. Difference in cracking
pressure and full-flow pressure
• cracking -- pressure at which valve begins
to open
• full-flow -- pressure at which valve is
allowing max flow

8. Obj 6. Two main types of pressure
reducing valves
• Constant reduced – Set to reduce a certain amount below the
operating system pressure.
– Ex. 1, Set constant reduced pressure at 500 psi and the system
pressure is 2000 pressure, the valve will keep the system pressure at
1500
– Ex. 2, Set at 500 psi and system pressure is 3000 pressure is reduced
to 2500
– Ex. 3, set at 250 psi and system pressure is 3000, the pressure is
reduced to 2750
– Also is ______ below the system pressure,
• Fixed amount pressure – Set to be one pressure no matter what
the system pressure is.
– Ex. 1, Fixed pressure is set for 1500 psi and the system pressure goes
to 2000 psi the pressure in the circuit stays the same at 1500
– Ex. 2, using info from Ex. 1, if the pressure goes to 3000 the pressure
stays the same in the circuit at 1500 psi.
– 1500 no matter what (unless total system pressure drops below 1500)

9. Obj 7. Function of a pressure
sequencing valve
• controls flow between branches/circuits
• first one then another branches/circuits

10. Obj 8. Function of unload valves
• Directs flow back to the reservoir

11. Obj 9. Five types of directional
control valves
1. Check valves
2. Rotary Valves
3. Pilot Operated Poppet Valves
4. Electro-hydraulic Valves
5. Spool Valves
1. Unibody
2. Stack

12. Obj 10. Difference in a valve stack
and a unibody valve

13. Obj 11 & 12 & 13 & 14. Types of
volume control valves
1. Flow control -- control amount of flow
1. Restrict flow -- Usually non-compensated--
Compensated valves do not adjust for
pressure changes
1. Needle (non-compensated)
2. Gate (non-compensated)
2. Divert flow -- usually compensated
2. Flow dividers – direct flow to two or more
circuits

14. Obj 12. Types of flow control valves

15. Obj 13. Types of flow divider valves

16. Obj 14. Proper procedures to follow
before & during valves disassembly

17. Obj 15. Proper procedures to follow
in reassembly of valves

18. Obj 16. Three ways valves can be
actuated/operated
• Operators for directional-control valves are
either;
– Mechanical or manual (many different ways to
manually operate a valve).
– Pilot – makes use of low volume system
pressure
– Electrical or Electronic
– A combination of the above

19. Obj 17. Common valve symbols