ABSTRACT
Pressure control limits the force/torque produced by an actuator. Because of the high power density of a fluid power circuit, pressure control is a critical safety, as well as functional, issue.
Five pressure-control valves (relief, unloading, sequence, pressure reducing, and counterbalance) are available. The principle of operation for all these valves is similar—a hydraulic force is opposed by a spring force. When pressure builds to the point where the hydraulic force is greater than the spring force, the valve spool is shifted, and flow is redirected. The relief, unloading, sequence, and counterbalance valves are all normally closed valves. Pressure rise at the valve inlet causes it to open. The pressure-reducing valve is a normally open valve, and pressure rise at the valve outlet causes it to close.
Pressure control is a key safety issue. Correct selection and functioning of the pressure control elements cannot be overemphasized.
