Hydraulic Valves

Question 1

Pressure relief valves can either be maximum pressure or ________?

Answer 1

Unloading valves

Question 2

What are the two basic designed of maximum pressure release valves?

Answer 2

Direct acting (simple relief)

Piloted operated relief (two stage or compound relief valves

Question 3

Where would you find direct acting relief valve?

Answer 3

Can handle small flows or where accurate control of pressure is not important.

Question 4

What are the three things relief valves perform?

Answer 4

Cracking pressure
Full flow pressure
Pressure override

Question 5

A maximum pressure relief valves uses 33.3% more energy to maintain full flow through it. Which valve will only use 5 % override?

Answer 5

Pilot operated relief valve

Question 6

Trouble shooting pilot operated pressure control valves

Question 7

What is the purpose of a sequencing valve?

Answer 7

To control the order of operation

Question 8

Problems and remedies for sequence valve.

Question 9

Why is a counter balance used?

Answer 9

Used to control vertical cylinders that are loaded so they do not fall freely due to gravity. Identical to sequence valves except the internal drain had replaced the sequence valves external drain.

Question 10

Counter balance faults and remedies

Answer 10

Question 11

Why are brake valves needed?

Answer 11

They prevent overspeeding when an overrunning load is applied

They prevent excessive build up when decelerating or stoping a load.

Question 12

Stack valves are bolted together in a stack and can control one or more actuators. What is the advantage of stacking valves?

Answer 12

More compact and less lines connecting the system together. Less chance for leaks.

Question 13

Why is used to seal the stacks together?

Answer 13

O rings

Question 14

What is the order of you should stack “stack valves”?

Answer 14

• Relief valve be placed closed to the sun plate so it can protect the whole system.
• flow controls are placed between pilot to open check valves and the actuator to avoid chatter.
• the directional control is placed at the top of the stack to supply pressure and flow controls.

Question 15

How is the stack valve supplied and drained?

Answer 15

Through the sub plate or manifold. Always at the bottom.

Question 16

The four ISO sizes for stack valves are:

Answer 16

Question 17

What is the advantage of a cartridge valve?

Answer 17

Very compact design, mounted to a manifold block. They are very popular because of there compact design and reduction of external hoses which are possible leak points.

Question 18

What are the two basic types of cartridge valves?

Answer 18

Screw in (30-35 gpa)

Slip in (large flow over 30 gpa

Question 19

Can you have multiple flow paths with slip in cartridges?

Answer 19

Yes you can select different sizes depending on the amount of flow needed for the required amount of flow.

Question 20

How is a slip in cartridge valve indicated if it is used as a flow control?

Answer 20

A triangle on the poppet

Question 21

In a slip in cartridge what is the designation for the pilot port?

Answer 21

Ap

Question 22

Which of the slip in or screw in cartridge valves can be re built?

Answer 22

Slip in

Question 23

What is the advantage of a proportional valve?

Answer 23

It can be moved to an infinite number of positions within its working rang by the varying electrical input

Question 24

What are the advantages of proportional valves?

Answer 24

• Simple design
• great accuracy
• simple circuit designs
• ideal for applications that can benefit from electronic control but do not require high accuracy
• more rugged and dirt tolerant the. Servo valves

Question 25

How do you vary the force in a proportional valve?

Answer 25

By varying the electrical input

Question 26

What type of spool is unique to proportional valves?

Answer 26

Notched spool.

They are used to accurately shift the spool and control the size of the port openings.

Question 27

What is the purpose of an amplifier card?

Answer 27

To increase the small signal from the input device.

Large power input is needed to drive the solenoid

Question 28

What is a dither signal for?

Answer 28

To help stop the spool from hanging up due to friction, magnetism in the solenoid, gravity or inertia in the spool

Question 29

What does LNVDT mean?

Answer 29

Linear variable differential transformer

Question 30

What is the difference between open loop (no feedback) and closed inner loop system and a closed outer loop system?

Answer 30

Open loop the controller cannot sense how accurately the actuator is responding to the control setting.

Closed inner loop system sends a signal to the controller to give it the position of the spool. (LVDT). Cannot correct inaccuracy.

Closed outer loop system connects a position sensor on the actuator to the summing junction in the amplifier control. Can correct the position of the actuator

Question 31

What are the three types of pressure controls for proportional valves?

Answer 31

Nozzle

Plate

Poppet

Question 32

Which pressure control should be mounted so that the solenoid is not at the top?

Answer 32

Nozzle type

This prevents air from becoming trapped in the core tube

Question 33

What is the advantage of the plate pressure control?

Answer 33

Highly responsive and accurate because they do not depend on springs to control the pressure

Question 34

What must you do after installing a proportional flow control?

Answer 34

Bleed the air from the ends of the solenoid.

Question 35

What is a servo valve?

Answer 35

Directional/flow control valve with an internal feedback mechanism built into the valve itself

Question 36

What is more accurate, servo valve or solenoid?

Answer 36

Servo valve