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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.

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

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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 isallowing 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 at1500

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 whatthe system pressure is.

Ex. 1, Fixed pressure is set for 1500 psi and the system pressure goesto 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 pressurestays 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 Valves4. Electro-hydraulic Valves

5. Spool Valves

1. Unibody2. 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

1. Restrict flow -- Usually non-compensated--

Compensated valves do not adjust for

pressure changes1. Needle (non-compensated)

2. Gate (non-compensated)

2. Divert flow -- usually compensated2. 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 ElectronicA combination of the above

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Obj 17. Common valve symbols

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