According to the principle of action, the pressure reducing valve can be divided into automatic or movable type. The automatic pressure reducing valve is a valve which reduces the pressure at the inlet end of the valve to a required outlet pressure through the throttling action of the opening and closing parts (discs). When the pressure and flow at the inlet end of the valve change, the valve can use the energy of its own medium to automatically adjust the flow rate to keep the pressure at the outlet basically stable. He-movable pressure relief valve is a valve which converts the pressure change into electric signal, and controls the actuator to make the valve move by electric signal, and keeps the outlet pressure basically stable at the regulated value.

The definitions are as follows:

Direct acting pressure relief valve: the use of outlet pressure changes, direct control of open and close parts (discs) movement of the valve.

Pilot pressure relief valve: by the pilot valve and the main valve, is the change of outlet pressure through feedback to control the main valve action valve.

Membrane type pressure reducing valve: diaphragm is used as the sensing element to drive the valve of the opening and closing part (disc) movement.

Piston type pressure reducing valve: piston is used as a sensing element to drive the valve of the opening and closing part (disc) movement.

Bellows pressure relief valve: the use of bellows as a sensitive element to drive the movement of the open and close parts (discs) of the valve.

Setting value: the outlet pressure value regulated by the pressure reducing valve according to the working condition.

Inlet pressure: medium pressure at the inlet end of the pressure reducing valve.

Outlet pressure: the pressure at the outlet of the pressure reducing valve.