Pressure Switch

What is Pressure Switch, How Do They Work?

22 May , 2021 News

A pressure switch is a device designed to give an output in response to a set level of pressure.

The switch makes electrical feedback on the rise or fall of pressure. The automated response of the switch is based on pressure. Its application ranges from industries to even residences and offices.

For example, it is often used in well pump systems, electronic gas compressors, security alarms, and pressure panels in sliding doors commercially.

A differential pressure switch is very similar to a regular pressure switch. However, in this case, the switch is activated when it senses a difference in pressure between two points.

There are two main categories of pressure switch types — mechanical pressure switch and electronic pressure switch. Their working principle is the same, with a slight difference in their structures and the pressure sensing element used. The most commonly used sensing elements are bellows, diaphragms, and pistons.

How Does it Work?

Before analysing its working principle, let’s look into the structure of a primary pressure switch.

structure of a primary pressure switchFollowing are the components of a pressure switch include:

(A) Micro-switch
(B) Operating pin
(C) Range spring
(D) Operating piston
(E) Insulated trip button
(F) Switch case
(G) Trip setting nut
(H) Inlet pressure

A modern-day pressure switch primarily contains a pressure sensor and a switch contact. Whenever the pressure level is reached, the switch contact activates the electric circuit or controls it.

A mechanical pressure switch along with the primary components uses a piston as the pressuring sensing element. However, the operating principle of this and the ones with bellow or diaphragm sensing elements remains the same.

As seen, the components remain inside the switch case (F); the inlet pressure (H) moves against the operating piston (D); the resulting pressure moves the spring (C). The range of the spring can be adjusted to a set pressure that activates the switch. The operating pin (B) that is activated by the motion of the spring and piston, in turn, triggers the micro-switch (A). The micro-switch has two components — usually close contact (NC) and normally open contact (NO); when the pressure switch is triggered, the micro-switch enables the electric circuit, making the switch work. In the absence of pressure, the micro-switch’s electric contact remains NO; when the set pressure is reached, the micro-switch activates the NO electric connection, closing the circuit.

Difference in the Working of a Mechanical and Electronic Pressure Switch:

The physical mechanism of a mechanical pressure switch is activated by fluid pressure, for example, in water pumps or hydraulic systems, whereas electronic pressure switches work through electronic pressure sensors and an electronic circuit. In some of the switches adjusting pressure point is not possible as it is pre-set.

Mechanical switches can work without any auxiliary power and are known to handle higher voltages better. On the other hand, electronic switches can be adjusted to change the delay time, output signal, deadband adjustability, turndown ratio etc.

Selecting the Right Pressure Switch:

For selecting the optimal pressure switch, the user needs to take into account the type of the process media, working pressure, temperature range, deadband or differential (the time between switch set and reset point), enclosure based on type of environments and finally, the type of the pressure switch depending on the application. For example for high-pressure application one should choose a piston design and for low pressure applications diaphragm operated switch is suitable. If you have any queries, Get in Touch with Us!