What Are The Parts And Principle of a Pressure Switch?

Pressure Switch:

A device that is designed to measure the pressure and give out output in order to show any changes in the pressure. This is done when the pressure is applied to a diaphragm or a piston which in turn produces a force which then gets checked with the spring that in its original position.

A pressure switch can find out the exact amount of air or liquid pressure. In most of the pressure switch Switzer, bellow or diaphragm type sensors are present. The way this diaphragm or bellow sensor moves causes a switch present inside to indicate with an alarm or start an action.

Every pressure switch has a different type of design and a different kind of sensing element which can be a bellow or diaphragm. One of the most common is the one with diaphragms or bellows as the sensing elements.

For this one, let’s have a look into a pressure switch that has a piston to sense the change in pressure. The piston run pressure switch also works on the same principle as a bellow type switch or a diaphragm switch works.

What are the parts of a pressure switch?

There are around 7 basic parts in pressure switches:

  • A Microswitch
  • A trip button that’s insulated
  • A pin for operating
  • A nut which is used to set the trip
  • Spring
  • A Piston that will be used as a sensing element
  • A case for the switch

A Microswitch

When the pressure flows through the switch, a microswitch is used to make or break a circuit. The micro-switch in the sectional view is a single pole double throw switch.

This switch is made up of one normally closed contact & an open contact. When the pressure switch starts operating, the normally opened contact gets closed and the normally closed contact opens up.

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Microswitches that have a gold contact are normally used on low voltage or the circuits that are considered safe as they have low voltage. if the circuit has high voltage then a silver contact is used instead of gold contacts.

A trip button that’s insulated

This button causes the normally opened and normally closed contacts to switch when the pressure switch actuates.

A pin for operating

The operating pin is attached to the operating piston. When the piston actuates as a result of inlet pressure changes, the operating pin either moves up and make contact with the trip button or moves down and breaks contact with the trip button.

A nut which is used to set the trip

The trip range screw is used so you could adjust the pressure switch’s setpoint. If you reduce the compression on the spring than this can be easily done. The lesser the compression, the lower the setpoint for the pressure switch.


This is a pre-compressed spring and the force generated by this determines the pressure at which the switch operates.

Piston that will be used as a sensing element

This is the part of the pressure switch in contact with the process. The process pressure acting upon the area of the operating piston generates the force that opposes that of the range spring.

A case for the switch

The enclosure containing the micro-switch and other accessories of the pressure switch is called the switch case or housing. For a switch with a pneumatic output two or more bulkhead connections are provided for the output connections. Switch housings are usually available in either aluminium or stainless steel.

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Operating Principle of a Pressure Switch

The inlet pressure is applied to the bottom of the operating piston. This piston is forced upwards by the inlet pressure against the range spring. The tension of the spring can be adjusted so that it is compressed at a certain pressure or setpoint. When this pressure is reached, the operating pin will hit the trip button on the micro-switch and change it over.

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