Pressure Switches Basics

What is the pressure switches?

A pressure switch is an instrument that automatically senses a change in the measured pressure and opens or closes an electrical switching element when a predetermined pressure is reached.

A pressure switch is a digital instrument as compared to other pressure gauges discussed so far, which are analog instruments. Pressure switches have pressure-sensing elements that make a small movement when the measured pressure varies. Most common sensing elements are:

  • Diaphragms

  • Bourdon tubes

  • Bellows

Working of a pressure switch:

The pressure measuring elements (sensors) produce the necessary movement to actuate the electrical switching element. These switches are normally snap acting single pole double throw (SPDT) types. Since they are SPDT switches, they have one normally open (NO) and one normally closed (NC) and one common © terminal to which electric power can be connected.

The switch is said to change over when the common pole changes from NC to NO. By doing this either the electric power can be connected or disconnected instantly on actuation of the switch. While connecting the power, check the nameplate details of the pressure switch for the contact rating to prevent burn out of the contacts.

Applications of Pressure switches:

  • Safety devices

  • Alarm

  • Control elements within a system

  • Steam power plant

  • Electric motors

  • Gas compressors

  • Boiler

  • Steam turbines