Pressure Switch

Pressure Switch

A pressure switch is a device that operates an electrical contact when a setpoint fluid pressure is reached. The switch makes an electrical contact on either pressure rise or pressure fall from a certain setpoint pressure level. Pressure switches are in a wide range of industrial and residential applications like HVAC systems, well pumps, Lube oil system ,furnaces etc.

Types Of Pressure Switches

There are two main types of Pressure Switches

• Mechanical Pressure Switch
• Electronic/Solid State Pressure Switch

Mechanical Pressure Switch

A mechanical pressure switch uses a spring and a diaphragm, or piston, to control at what pressure the micro-switch is operate. The spring is the opposing force to the inlet pressure and the springs tension is adjusted with a set screw or knob. The spring tension directly correspond to the pressure at which the switch makes an electric contact. When the pressure decrease, the switch resets to its original position. The difference between the switch point and reset point is called hysteresis. These pressure switches usually have three different types of contact: normally open (NO), normally closed (NC), and changeover (COM) contacts. Changeover contacts are for both NO and NC operation.

The mechanical pressure switch is better suited for handling high voltages and amperages than an electronic pressure switch. They can be used to make a contact change for an increase or decrease in pressure.   

In picture contact set shown no.1,2 and 4 here no.1 terminal use as COM,no.2 terminal use as NC and no.4 use as NO

Types Of Mechanical Pressure Switch

• Diaphragm Pressure Switch
• Piston Pressure Switch
• Differential Pressure Switch
• Burden Tube Pressure Switch

Diaphragm Pressure Switch

It is Diaphragm based pressure Switch. Switch includes a metal membrane that is connected directly to the  part of the switch and the diaphragm that activates the switch. This switch is used for monitoring pressure and control of processes in different industries like chemical, petrochemical, gas and oil.

Piston Pressure Switch

This switch having a piston which is moves the pressure of liquid varies, the piston is axially position so that it operate the switch. This switch can detect the pressure of liquid directly or indirectly. So directly detecting mainly involves seals like O-rings to avoid the liquid from getting into the components whereas indirect detecting mainly involves a flexible diaphragm that divides the piston from the liquid.

Differential Pressure Switch

This switch is very useful in differentiating the forces between two points within a system. The two points within the system are simply connected to two process ports which are the upside or downside of the equipment. If the difference in pressures between the two sides increases a certain threshold, then a switch can be operate. These switches are applicable in monitoring pressure fall across screens, filters & tank levels.

Burden Tube Pressure Switch

This is an elliptical and flexible metallic tube that is connected to one end of the switch whereas another end is free to move. Once liquid pressure is increased within the tube, then it try to make a level, then this movement is mainly used to activate the switch. These switches are suitable for different applications like chemical, conventional power stations, and petrochemical etc.

Electronic Pressure Switch

Electronic pressure switch is solid-state switch that do not require actuation from the pressure-sensing element to operate the switch. They operate indirectly by using other properties, such as resistance and capacitance.

An Electronic Pressure Switch has basically three sections shown in the picture above.
Pressure sensor is measure the pressure and the other section controls electronics is initialized control when desire pressure is reached and we have last section Electrical connection analyze co-connection which is allow automatically control our equipment.

FAQ

What is a pressure switch used for?
The purpose of a pressure switch used to automatically activate or deactivate another device when a certain pressure is reached.

 How does a pressure switch work for water?
As water enters the tank, the level of water increases then the pressure increases. Once the pressure reaches the set point, the switch turns the pump off until water level decrease then the pressure will be decrease the pump will turn on again.

What is a pressure switch for HVAC?
An HVAC pressure switch is a optimal performance and enhance safety that is installed in both heating and cooling systems. The switch will open and cause the system to stop operating under certain conditions which may damage the system.

How do you test a pressure switch?
A pressure switch can test 3 ways but easy way to test by multimeter checking its resistance.
select the multimeter selector nob on resistance value after that check the terminal of pressure switch the resistance should be zero otherwise pressure switch is faulty.