Pressure switches are devices that are turned on or off when ever there is a drop in the pressure of a liquid or gas, against which they have been placed. When the target pressure is reached the switches automatically open/ close an electrical circuit, sound an alarm, open or close a solid state switch or electromechanical switch. Some common types of pressure switches are: gauge, differential, absolute, vacuum and sealed. These safety switches can be used to start and stop motors and fans, open doors, turn on and off lights and alarms, and anything else that can be activated by a switch. Because of their function, pressure switches are very valuable to many types of industries and they have averted many accidents over the years. Along with pressure gauges, these switches make sure that high pressure gases are within the safe levels.
The throw of the pressure switch can be either single or double throw. There are different styles of pressure switches such as: indicator, sensor element, transducer, chip, meter, gauge, recorder, totalizer and controller. There are also various types of pressure sensing units that are used in the pressure switch such as: MEMs, piston, diaphragm, piezoelectric, strain gauge, variable capacitance, semiconductor piezoresistive and vibrating element.
Generally, a pressure switch will contain a diaphragm that is filled with air. When the air pressure changes, the sides of the diaphragm will move and push against or move back from a calibrated spring. The movement of the spring is transformed to a snap switch, which is triggered when the air pressure increases or decreases. The spring is calibrated so that a specific amount of movement is equal to a change in the air pressure. If a pressure switch notices a change in air pressure and is activated, it takes a specific amount of air pressure to be taken from or added to the system to reset the calibrated spring.
The accuracy of the pressure switch is very important and periodic calibration is required to make sure that it is working correctly. The switches must be able to sustain reasonable levels of shock, vibration and fluctuations in temperatures. Pressure switches have temperature variation compensation features to take care of any minor fluctuations. The switches must be properly mounted near the sensing zone.