All About Pressure Switches! – PSI Automation

All About Mechanical Pressure Switches!

The low-cost and reliable pressure sensor

All About Mechanical Pressure Switches!

The low-cost and reliable pressure sensor

What are Pressure Switches?

Pressure switches are used to operate an electrical contact when a certain pressure in a liquid or gaseous medium is reached. They can be used to switch another device on or off from rising or falling pressure.

They are sometimes referred to as electro-mechanical pressure switches or pressure sensors.

It is important to not confuse them with pressure transducers or pressure transmitters, which convert pressure into an electrical output signal.

There are two types of pressure switches, mechanical and electrical. Today we will be talking about mechanical pressure switches.

How do mechanical pressure switches work?

Firstly, let’s look at what makes up a pressure switch.

Parts of a mechanical pressure switch

A pressure sensing element, usually a diaphragm or piston that acts as the pressure detection element.
An adjustment screw to vary the set point.
A spring to provide resistance against the pressure sensing element
Switch contacts that allow current from an external power source to pass through them when they touch.
Terminals to connect the external power source to the contacts.
Process connection, a threaded port to the switch to the process unit

In the demonstration below, we can see that the pressure switch is connected to the system at the process connection.

Here the system is not pressurised, therefore the diaphragm is in a resting position, and the electrical contacts are not touching.
As we increase pressure in the system, it causes the diaphragm to collapse and compress the spring.
Once the spring compresses enough to reach the set point, the electrical contacts touch, and a circuit is created.

This demonstration features a normally open switch, as the circuit remains open at rest, they are also made as normally closed.
However, for ease of functionality across multiple applications, they are commonly manufactured to have both NO and NC components, we call this “changeover“.

How to choose a pressure switch

Pressure switches come with a vast array of options. In order to select the correct pressure switch for your system, it is important to gather as much information as you can.

Below are the vital pieces of information we need to select the perfect switch for your application:

Pressure range or switching point – the pressure you require it to switch at, and whether it is rising or falling
Port size – usually ⅛” or ¼ and BSP or NPT
Switch type – Normally open, normally closed, or changeover
Electrical connection – usually a DIN plug, flying leads, or spade terminals
Body material – usually brass, steel, stainless steel, or plastic
Pressure sensing component – we typically stock diaphragm type switches. These come in a few material options including Nitrile (NBR) as a standard, or Viton, and EPDM options.
Maximum system pressure – also referred to as overpressure