Working principle of pressure relay

A pressure relay is a hydraulic and electrical conversion element that uses the pressure of a liquid to open and close electrical contacts. When the pressure of the system reaches the set value of the pressure relay, it sends out the electric signal, which makes the electrical components (such as electromagnets, motors, time relays, electromagnetic clutches, etc.) move, makes the oil circuit unload and change direction, performs the sequential action of the components, or closes the motor so that the system stops working, and plays a safe and protective role.

The pressure relay has four structural forms: plunger type, diaphragm type, spring tube type and bellows type. The following pair of plunger type pressure relays has a brief introduction for the work principle.

When the liquid pressure entering from the oil inlet of the lower end of the relay reaches the set pressure value, the plunger is pushed upward. The displacement is amplified by the lever and the micro-switch is pushed forward. Changing the compression amount of spring can adjust the action pressure of relay.

Application occasions: for safety protection, control of the sequential action of the executive components, for the opening and closing of the pump, for the unloading of the pump.

Note: the pressure relay must be placed in a place where the pressure changes significantly to produce electrical signals. If the pressure relay is placed on the return circuit, the pressure relay will not work because the return circuit is directly connected to the tank and the pressure does not change.