Hydraulics. Hydraulic Pressure Control

Transcription

1 Hydraulics Hydraulic Pressure Control

2 Direct Acting Pressure Relief Valve Normally Closed:

3 Pilot Operated Relief Valve (Compound/ two stage) Small pilot relief valve + Main relief valve

4 Pilot Operated Relief Valve (Compound/ two stage)

5 Pilot Operated Relief Valve (Compound/ two stage)

6 Pilot Operated Relief Valve with remote control

7 Pilot Operated Relief Valve with remote control Whenever pump flow and pressure are not needed:

8 Pressure Override: Pressure Override= Full-flow pressure - cracking pressure

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10 Cross-over Pressure Relief Valve Preventing shifting shock in motor Provides a shock absorbing or cushioning effect

11 Unloading Valve: An unloading valve reads the pressure in an external line, rather than in its own line Both relief and unloading valves send flow back to the tank

12 Unloading Valve Circuit:

13 Unloading Valve Circuit: Example: metal stamping machine High flow (speed)-low pressure (force) in a part of the stroke Low flow (speed)- high pressure (force) in another part of the stroke

14 Unloading Valve Circuit:

15 Pressure Reducing Valve: Maintain a reduced pressure level in a branch circuit of a hydraulic system The reducing valve reads the pressure downstream( after the valve) The relief valve reads the pressure upstream( before the valve) Normally close Normally open

16 Pressure Reducing Valve Application: Energy loss Heat Generation

17 Sequence Valve: Sequence valve is a pressure valve that is used to force two actuators to be operated in sequence Instead of sending flow back to the tank, a sequence valve allows flow to a branch circuit when a present pressure is reached

18 Sequence Valve Application: A clamp cylinder extends first to hold a work piece, then a second cylinder extends to bend the work piece into a desired shape

19 Sequence Valve Application: Setting by trial and error

20 Sequence Valve Application: Both cylinders retracting

21 Sequence Valve Application: The bending cylinder will extend only after the clamp cylinder is fully extended and the clamp cylinder will retract only after the bending cylinder is fully retracted

22 Counterbalance Valves: Counterbalance valves are pressure control valves that are used to prevent a load from accelerating uncontrollably

23 Counterbalance Valves: When the DCV is shifted to lower the weight, the cylinder will not extend until a preset pressure is reached in the rod end The check valve allows the counterbalance valve to be bypassed when the cylinder is retracted Sequence valve requires an external drain, while a counterbalance valve does not because it can be drained internally Setting by trial and error

24 Brake Valves: Like counterbalance valves are used to prevent load from accelerating uncontrollably counterbalance valves are used with cylinders; brake valves are used with hydraulic motors Commonly used in circuits in which the motor must lower a large weight When the weight is lowered, it may tend to drive the motor, instead of the motor lowering the weight (overrunning) (motor acting as a pump!!!!!) Sensing the pressure at both sides A simple winch circuit

25 Pressure-compensated Pumps: Have the ability to limit the maximum pressure in a hydraulic circuit by reducing their displacement Decreasing due to leakage

26 Pressure-compensated Pumps: Hydraulic press circuit Pressure must be maintained for a period of time The valve could not go to the neural due to leakage and then pressure drop Heat generation

27 Pressure-compensated Pumps: Hydraulic press circuit Rule of thumb: pressure relief valve 10% higher than the compensator setting

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