The valves enable the regulation of system pressure to adjust the force on a hydraulic piston rod or the torque on a hydraulic motor shaft. Pressure relief valves are used to set the maximum pressure in the circuit and protect it from overloading. Pressure reducing valves permanently maintain the output pressure at the set value while protecting the appliance from overloading. Unloading valves are designed for economical pressure control in accumulator-operated circuits that serve as a power source for emergency control.