Valves - Part A Flashcards
Pressure reducing valves
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Pressure relief valves
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Unloading valve
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Why would you need an external drain on a valve
- there could be pressure downstream
- pressure reducing valve
- sequence valve
Right angle check valve
-can handle larger flow because the poppet moves out of the path of flow
Difference between counterbalance and brake valve
- 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
Restrictor compensator
- restricts the flow to the main throttle
- maintains speed throw pressure and temperature fluctuation
Reverse flow bypass
- 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
Bypass compensator
- maintains speed regardless of pressure
- only works with meter in
- has a built in overload relief valve 20psi
Pilot to open check valves
- 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.
Pilot to close check valve
- normally open and held open by a spring
- used to ensure the accumulator is depressurized when the pump is shut off
4 ways to unload a pump
- venting a relief (remotely)
- unloading relief
- on/off valve (when using an accumulator)
- pilot operated unloading valve (2 pump system)
Pressure compensator
- (hydrostat) used to ensure steady flow regardless of changes in the load pressure
- when it senses an increase in load it increases the flow
Types of pressure compensators
- 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)
Check valves
- 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
Pressure compensator
- (hydrostat) used to ensure steady flow regardless of changes in the load pressure
- when it senses an increase in load it increases the flow
Types of pressure compensators
- 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)
Types of directional control valves
-rotary spool, sliding spool and poppet (check valve)
Pilot chokes on DCV’s
-allows a quick or gradual response to the main spool
Regenerative DCV centre
-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.
Temperature compensator
-maintains speed when temperature fluctuates
Overspend control valve
-prevents speed increase if DCV is suddenly shifted
Pilot lines for valves
-are behind the arrow normally closed valves and in front of the arrow for normally closed valves
Charge pump
- re-circulates case drain flow
- primary pump to drive motor
- circulates oil through filter and cooler when required
External pilot
- increases the download force capability
- bad if something happens to that line the valve the valve won’t open.
Pressure override
-the pressure above the max relief setting in order to raise and keep the poppet raised in the max relief valve in direct acting
Cross port relief valve
-used with a bi-directional motor to control motor speed, similar to a brake valve with a uni-directional motor.
