Pressure Switch - Types, Applications, And How They Work

Switches are used for making and breaking connections within an electric circuit. Different kinds of switches are available in the market catering to various requirements, and pressure switches are one of the most used. 

The role of a pressure switch is to activate an electrical contact on reaching a specific liquid pressure. Along with maintaining the pressure of the fluid for retaining the normal levels of the system, pressure switches also guard the equipment against harm. 

This article covers various aspects of a pressure switch. Read on to know more. 

What is a pressure switch?

Before understanding what is the use of a pressure switch, we have to first know what a pressure switch is. A pressure switch is an electronic or mechanical device, which gets activated by the pressure of air, fluids or gas when air, fluids or gases reach a set point or a threshold level. Major components of pressure switches are pistons, bourdon tubes, and membranes or diaphragms which deform or move with the pressure exerted by the system. These various components are connected to one or more contacts in the switch. Abundant force is needed for opening or closing the switch, depending on its configuration. 

Also Read: An Essential Guide to Understanding Pressure Switches

Pressure switches detect pressure via different methods and are accordingly categorized as electronic or electromechanical switches.  Places, where pressure switches are commonly used include pumping systems, compressed gas systems, instrumentation systems, and HVAC systems. 

Construction of an electronic pressure switch

To understand how a pressure switch works, you need to know the construction of the switch along with its vital components. There are various key components which make up a pressure switch and they are:

• Diaphragm – The function of the diaphragm is to detect pressure. The material used for making the diaphragm is sensitive and pliable to pressure. 

• Lever – The lever activates and deactivates the switch. 

• Spring – The spring is flexible and is used for adjusting the cut-out points or set points. 

• Terminals – Terminals are the areas where the external power source connects to the contacts. 

• Electrical contacts – It is evident from the component’s name that electrical contacts allow the passage of current through them from the external power source. 

For the functioning of a pressure switch, the main component that is required is the presence or the absence of pressure. Diaphragm pressure compresses the spring in the pressure switch. When the spring tension exceeds the setpoint or cut-out point, it will close the contacts in a NO switch and open them in the NC switch. 

Variants of electronic pressure switches 

‘How many types of pressure switches are available’, is a common question that many people ask. To answer the question - there are two main variants of electronic pressure switches – mechanical pressure switches and electronic pressure switches. There are sub-variants under these switches too. 

• Electronic pressure switch

An electronic pressure switch comes with a pressure transducer, mainly with a strain gauge and with additional proprietary electronics for amplifying and converting signals into a readable display. Some electronic pressure switches come with analogue features too. These switches have switching capabilities and they can transmit variable and continuous signals representing the pressure reading. Some prominent features of an electronic pressure switch include switching function, on-site programmability of time delay, hysteresis, and setpoint. 

• Mechanical pressure switch

Mechanical pressure switches are more commonly used when compared to electronic pressure switches due to their lower cost and simplicity. These switches come with a mechanical pressure-sensing component which deforms according to the fluid pressure applied. Depending on the pressure sensing component, mechanical pressure switches have different classifications. Some of the common ones are as follows:

• Diaphragm pressure switch – This pressure switch contains a metal membrane which is joined directly to the wetted part of the switch and the diaphragm actuates the switch. 

• Bourdon tube pressure switch – The bourdon tube is a flexible elastomeric or metallic tube, which is fixed at one end and one end is free to move. It straightens when pressure increases inside the tube and this movement actuates the switch. 

• Piston pressure switch – This is the most common and popular pressure switch. With a change in fluid pressure, the piston moves axially, activating the switch. 

• Differential pressure switch – This pressure switch is used for comparing pressures between two points in any system. When the pressure between the two points exceeds a particular threshold, the switch is activated. 

Pressure switch selection criteria

While selecting pressure switches, there are several factors that you need to keep in mind. Some of the most important ones are as follows:

• The fluid used
• The pressure ranges
• The type of pressure which needs to be applied
• Operating temperature of the system
• Control system voltage
• Service life
• Fittings
• Certifications, and so on. 

Always buy pressure switches from a known and reliable brand