Valves - Part A

Question 1

Pressure reducing valves

Answer 1

-

Question 2

Pressure relief valves

Answer 2

-

Question 3

Unloading valve

Answer 3

-

Question 4

Why would you need an external drain on a valve

Answer 4

• there could be pressure downstream
  - pressure reducing valve
  - sequence valve

Question 5

Right angle check valve

Answer 5

-can handle larger flow because the poppet moves out of the path of flow

Question 6

Difference between counterbalance and brake valve

Answer 6

• brake is only after a motor and counter is after a cylinder
• brake has in external pilot before the motor and an internal for after the motor. Counter can have an internal or external

Question 7

Restrictor compensator

Answer 7

• restricts the flow to the main throttle

- maintains speed throw pressure and temperature fluctuation

Question 8

Reverse flow bypass

Answer 8

• allows fluid to return to tank through the valve as long as the reverse pressure is less than the system pressure
• allows speed control in one direction and full speed in the other

Question 9

Bypass compensator

Answer 9

• maintains speed regardless of pressure
• only works with meter in
• has a built in overload relief valve 20psi

Question 10

Pilot to open check valves

Answer 10

• normally closed
• can be used to lock cylinder in place similar to a counterbalance.
• area ratio must be greater than area ratio of cylinder
• can be opened by a pilot to allow flow in opposite direction.

Question 11

Pilot to close check valve

Answer 11

• normally open and held open by a spring

- used to ensure the accumulator is depressurized when the pump is shut off

Question 12

4 ways to unload a pump

Answer 12

• venting a relief (remotely)
• unloading relief
• on/off valve (when using an accumulator)
• pilot operated unloading valve (2 pump system)

Question 13

Pressure compensator

Answer 13

• (hydrostat) used to ensure steady flow regardless of changes in the load pressure
• when it senses an increase in load it increases the flow

Question 14

Types of pressure compensators

Answer 14

• bypass (has a built in overload relief valve, only works with meter in because pilot passage is on the downstream side)
• restrictor (restricts flow to the main throttle spool when the load drops, requires a reverse flow check valve)

Question 15

Check valves

Answer 15

• always flow in one direction and are drawn opposite of intended flow.
• they reduce flow because the ball valve blocks partial flow, except the right angle check valve

Question 15

Pressure compensator

Answer 15

• (hydrostat) used to ensure steady flow regardless of changes in the load pressure
• when it senses an increase in load it increases the flow

Question 16

Types of pressure compensators

Answer 16

• bypass (has a built in overload relief valve, only works with meter in because pilot passage is on the downstream side)
• restrictor (restricts flow to the main throttle spool when the load drops, requires a reverse flow check valve)

Question 17

Types of directional control valves

Answer 17

-rotary spool, sliding spool and poppet (check valve)

Question 18

Pilot chokes on DCV’s

Answer 18

-allows a quick or gradual response to the main spool

Question 19

Regenerative DCV centre

Answer 19

-when you need more speed for the cylinder you can slide the spool to this position and it will send the fluid from the rod end to the cap end. However, doing this will create back pressure on the rod end and reduces he force that can be delivered.

Question 20

Temperature compensator

Answer 20

-maintains speed when temperature fluctuates

Question 21

Overspend control valve

Answer 21

-prevents speed increase if DCV is suddenly shifted

Question 22

Pilot lines for valves

Answer 22

-are behind the arrow normally closed valves and in front of the arrow for normally closed valves

Question 23

Charge pump

Answer 23

• re-circulates case drain flow
• primary pump to drive motor
• circulates oil through filter and cooler when required

Question 24

External pilot

Answer 24

• increases the download force capability

- bad if something happens to that line the valve the valve won’t open.

Question 25

Pressure override

Answer 25

-the pressure above the max relief setting in order to raise and keep the poppet raised in the max relief valve in direct acting

Question 26

Cross port relief valve

Answer 26

-used with a bi-directional motor to control motor speed, similar to a brake valve with a uni-directional motor.