Hydraulic Valves

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Hydraulic Valves
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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.
• Describe the proper procedures to follow in
  reassembly of valves.
• List and describe three ways valves can be
  actuated/operated.
• Identify six common valve symbols

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Obj 1. Functions of a valve

• direct the flow of fluid
• regulate the pressure
• control volume

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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

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Obj 3 Uses of pressure control valves

• Limit system pressure
• Reduce pressures
• Set pressure at which oil enters a circuit
• Unload a pump

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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

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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

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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)

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Obj 7. Function of a pressure sequencing valve

• controls flow between branches/circuits
• first one then another branches/circuits

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Obj 8. Function of unload valves

• Directs flow back to the reservoir

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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
6. Unibody
7. Stack

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Obj 10. Difference in a valve stack and a unibody
valve
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Obj 11 12 13 14. Types of volume control
valves

1. Flow control -- control amount of flow
2. Restrict flow -- Usually non-compensated--
   Compensated valves do not adjust for pressure
   changes
3. Needle (non-compensated)
4. Gate (non-compensated)
5. Divert flow -- usually compensated
6. Flow dividers direct flow to two or more
   circuits

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Obj 12. Types of flow control valves
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Obj 13. Types of flow divider valves

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Obj 14. Proper procedures to follow before
during valves disassembly
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Obj 15. Proper procedures to follow in reassembly
of valves
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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

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Obj 17. Common valve symbols
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