Hydraulics Hydraulic Pressure Control
Direct Acting Pressure Relief Valve Normally Closed:
Pilot Operated Relief Valve (Compound/ two stage) Small pilot relief valve + Main relief valve
Pilot Operated Relief Valve (Compound/ two stage)
Pilot Operated Relief Valve (Compound/ two stage)
Pilot Operated Relief Valve with remote control
Pilot Operated Relief Valve with remote control Whenever pump flow and pressure are not needed:
Pressure Override: Pressure Override= Full-flow pressure - cracking pressure
Cross-over Pressure Relief Valve Preventing shifting shock in motor Provides a shock absorbing or cushioning effect
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
Unloading Valve Circuit:
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
Unloading Valve Circuit:
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
Pressure Reducing Valve Application: Energy loss Heat Generation
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
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
Sequence Valve Application: Setting by trial and error
Sequence Valve Application: Both cylinders retracting
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
Counterbalance Valves: Counterbalance valves are pressure control valves that are used to prevent a load from accelerating uncontrollably
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
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
Pressure-compensated Pumps: Have the ability to limit the maximum pressure in a hydraulic circuit by reducing their displacement Decreasing due to leakage
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
Pressure-compensated Pumps: Hydraulic press circuit Rule of thumb: pressure relief valve 10% higher than the compensator setting