Pressure switch Working Principle

Pressure Switch

A pressure switch is a form of switch that makes electrical contact when a certain set pressure has been reached on its input. This is used to provide on/off switching from a pneumatic or hydraulic source. The switch may be designed to make contact either on pressure rise or on pressure fall.

This is a device designed to monitor a process pressure and provide an output when a set pressure (setpoint) is reached. A pressure switch does this by applying the process pressure to a diaphragm or piston to generate a force which is compared to that of a pre-compressed range spring.


pressure switch

Pressure Switch has 3 contacts.


NO (Normally Open)

NC (Normally Closed)

A spring is used in pressure switch when pressure increases this spring comes in tension. A pressure is also set using adjusting screw when increasing or decreasing pressure comes to this pressure contact changes from NC to NO or from NO to NC.

A differential pressure is also used In pressure Switch. In this pressure Switch, two Pressures are used.

1.Differential Pressure.

2.main Pressure.

Let Suppose main Pressure is 4kg/cm^2 and Differential Pressure is 1 kg/ cm^2, then on increasing pressure contact will change from NC to NO at 5 kg/cm^2 and on decreasing pressure from NO to NC at 3 kg/cm^2.


Pressure switch

The connection of a Pressure Switch

2 wires are connected in a pressure switch

One is connected in common and other is connected in NO or NC according to the application.


Pressure Switch Connections

How to check a pressure switch

  • Step 1: first we check the continuity between common between normally closed (NC).
  • Step 2: Now after increasing the pressure when pressure is equal to set pressure we check the continuity between common and normally open (NO).
  • Step 3: now we will decrease the pressure and when decreasing pressure is equal to the set pressure again we will get continuity between common and normally closed (NC).