Hydraulic press relief valve is a kind of control valve, mainly plays the role of constant pressure relief, pressure stabilization, system unloading and equipment safety maintenance. Constant pressure relief effect: In the constant pressure pump energy-saving regulation system, the constant pressure pump provides a stable flow rate. When the system pressure increases, the flow demand will decrease. At this time, the relief valve of the hydraulic press opens so that the residual flow can overflow back to the tank, ensuring that the inlet pressure of the hydraulic press relief valve, i.e. the pump outlet pressure, is stable (the valve opening is often opened with the pressure wobble).

　　Hydraulic press relief valve generally has two structures: 1. Direct-acting hydraulic press relief valve 2. Pilot-operated hydraulic press relief valve.

　　The main requirements of hydraulic press relief valve are: large regulating range, small regulating error, small pressure fluctuation, sensitive action, large overload and low noise.

　　The hydraulic press directly driven by oil pump has the following characteristics:

　　1. The travel speed of the movable cross beam of the hydraulic press depends on the liquid supply of the pump and has nothing to do with the deformation resistance of the forging in the process. If the supply of liquid from the pump is constant, the operating speed of the hydraulic press is a fixed value.

　　2. The sum power consumed by the pump is related to the deformation resistance of the machined workpiece. If the operation deformation resistance is large, the sum power consumed by the pump is also large, and vice versa.

　　3. The uniform speed movement of the movable beam and the change of the pump supply force can be used as the signal of the operating distributor to complete the automatic control of the hydraulic press.

　　4. Low investment, small floor space and simple daily maintenance. The pump in the pump direct drive system is selected according to the larger working speed and pressure of the hydraulic press, but when the hydraulic press is short in filling stroke, return stroke, auxiliary process and required working pressure, the pump is not fully utilized, especially for the large tonnage hydraulic press, the utilization factor is very low. Therefore, hydraulic presses tend to drive the operating speed and pressure in stages.