Hydraulic Valves Flashcards
What is a hydrostat?
A pressure compensated flow control
What are the three types of servo valves?
flapper nozzle
Jet pipe
Staging spool
What are four ways to unload a pump?
vent the relief
Unloading relief valve
On off valve
Pilot operated unloading valve
What is the purpose of a pilot to open check valve?
Valve can be opened by a pilot to allow flow in the opposite direction
What are the three types of pressure controls in a proportional valve?
nozzle
Plate
Poppet
where are brake valves used and what do they do?
They are used on the discharge from hydraulic motors.
They prevent over speeding and excessive pressure buildup when stopping or slowing down a load
what are transducers?
Sensors that measure position, pressure or velocity
what are the two main components of a servo valve?
Torque motor
Spool valve
What is a servo valve?
A directional or flow control valve with an internal feedback mechanism built into the valve
what is a proportional valve?
A solenoid operated valve that uses a proportional solenoid
What are the five types of pressure control valves?
Relief valves, pressure, reducing valves, sequence valves, counterbalance valves, and brake valves
what is the purpose of an amplifier card?
To increase the signal from the pilot device
What can proportional valves be used for?
to stop an actuator at any point in its stroke.
Control the speed of an actuator.
Control the acceleration and acceleration of an actuator.
What is a dead band compensator
It briefly boost the power to make the spool jump across the overlap distance between ports
what is gain?
The number of times the output voltage is greater than the input voltage
Output/input
What is hysteresis?
A term used to express how accurately the spool moves compared to the input current
what is dither?
A small high frequency, alternating current applied to the solenoid to prevent the spool from getting hung up/stuck
what is the purpose of an overspeed control?
It prevents a sudden Russia fluid through the flow control when the directional control is suddenly opened
what is the purpose of a pilot to close check valve?
Valve is held open by a spring and closed by a pilot to prevent reverse flow
what are the four control functions in an amplifier card?
Dead compensation
dither signal
Gain
Ramps
What are the two types of pressure compensators?
bypass
Restrictor
What are three types of valve elements to control flow in a directional control valve?
sliding spool
Rotary spool
Poppet
what are the two types of pressure relief valves?
Maximum relief valve
Unloading valve
what six input devices provide signals to the amplifier card?
joystick
PLC
potentiometers
Temperature sensor
Pressure transducers
Tach generators
what is used to to control the electrical input of a proportional valve?
Amplifier card
what is the ramp function?
It controls how fast the voltage to the solenoid is increased or decreased
- it controls acceleration and deceleration*
what is special about a proportional solenoid?
It can move to an infinite number of positions
what is metre in flow control?
Controls the flow going into the cylinder to control its speed
Controls extension and retraction
Where would you place a metre in flow control valve if you want to control extension and retraction?
Before the directional control valve
what happens if the spring on a sequence valve is set too low?
The second cylinder will move too soon
what is venting a relief valve?
Unloading the entire system from our location, remote from the relief valve
What are the three types of flow control valves?
metre in
Metre out
Bleed off
what happens if the spring on a sequence valve is set too high?
The second cylinder will not move
What are the three types of control valves?
pressure control
Flow control
directional control
what are metering notches?
Notches in the school that control the flow rate from the valve
where is the relief valve placed on the stack valve?
Closest to the sub plate
where is the directional control valve placed on a stack valve?
At the top of the stack
what is the difference between a stack valve and a cartridge valve?
Cartridge valves use a poppet stack valves use a spool
what are the two types of cartridge valves?
Screw in
Slip in
What is the main advantage of a proportional valve over a servo valve?
They are more rugged and dirt tolerant
what is the purpose of an open school centre design?
It allows the pump to circulate freely, but does not lock the cylinder
what is the purpose of a closed spool centre design?
It locks the cylinder and blocks the flow
What is the purpose of a float spool centre design?
It shuts off the pump flow, but allows motor to coast freely
what is the purpose of a tandem school centre design?
It locks the cylinder, but allows the pump to circulate back to the reservoir
