Mechatronics Essay

3759 Words Aug 14th, 2011 16 Pages
Poppet or check shut off valves
Pressure relief valve simulation
Function
Leak free sealing of flow in one direction.
Allows flow in only one direction.
Provides positive back pressure on a system when fitted with a spring.
Also used as simple low pressure relief valves.
Setting
Fixed spring to control the opening or cracking pressure
Fit valves without springs vertically
Variations
Pilot operated – can be opened by pilot pressure to allow flow back through valves.
Can be used as leak free directional valves. Typically for low flow, high pressure situations or for very high flows where directional valves are expensive or not suitable.
Directional control valves
Function
Stops/starts flow or directs flow into A or B service
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Setting
Can only reduce system pressure not increase it.
Pilot pressure - Changes in pilot drain or backpressure can effect the pressure setting.
Variations
Pilot or direct operated
Backflow capability - Some systems require backflow capability in case downstream pressures go up as well as down.
Pilot operated - controls setting remotely.
Proportional control valves
Function
Proportionally control the flow into the A or B lines depending on the angle of a hand leaver or value of electrical control signal.
Also available as proportional relief and reducing valves.
Setting
Proportional valves require a significant pressure drop across the valve to accurately control the flow, say 30 bar.
Require good fluid cleanliness
Require suitable electrical control cards
Variations
Manual or electrical operation.
Spool centre leakages vary depending on free flow path or pressure venting.
Pilot or direct operated valves. Low flows generally direct acting, large flows piloted.
Valve response times may vary.
Control pressure drop across valve to give repeatable flow accuracy independent of system.
Servo directional control valves
Function
Very accurately control the flow into the A or B lines depending on the electrical control signal. Generally used in high performance closed loop control systems.
Setting
Servo valves require a significant pressure drop across the valve to accurately control the

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