Pressure Switches applications and principle

A pressure switch is a device that operates electrical contacts when a preset fluid pressure is reached.The switch makes electrical contact when the pressure rises or falls from a certain preset pressure level.Pressure switches are widely used in industrial and residential applications such as HVAC systems, well pumps,furnaces,etc.A pressure switch should not be confused with a pressure sensor.Pressure transducers convert pressure into an electrical output. signal

Mechanical pressure switch 

Mechanical pressure switches use a spring and diaphragm or piston to control the pressure that triggers a micro-switch.The spring is the force that opposes the inlet pressure,and the spring preload is adjusted by a set screw or a knob.Spring preload is directly related to the pressure with which the switch makes electrical contact.When the pressure drops,the switch resets to its original state.The difference between switch point and reset point is called hysteresis.This is usually expressed as a percentage of the switch point value,eg 20%. Hysteresis is defined by the manufacturer and is not user configurable for most mechanical switches.These pressure switches typically have three different types of contacts:normally open (NO),normally closed (NC) and changeover (SPDT) contacts.Changeover contacts are available for NO and NC operation.Mechanical pressure switches are better at handling high voltages and amperages than electronic pressure switches.They can be used to alter contact to increase or decrease pressure.

Electronic pressure switch

Electronic pressure switches use an electronic pressure sensor to measure changes in inlet pressure.They have digital displays to set switch functions. Switch points can be set by the manufacturer or field programmed according to application requirements.Switching point,output signal,hysteresis,delay time, etc.are some of the functions that the user can adjust according to their needs.Electronic pressure switches are suitable for use in automated and controlled equipment systems requiring programmable functionality,digital display,flexibility,accuracy,ingress protection,and stability.

Working principle

The pressure switch shown in Figure is an example of a single-pole double-throw (SPDT) switch,which operates on a mechanical principle.All components are inside the switch box (F), which has an inlet pressure port (H).Briefly,inlet pressure pushes piston (D) against spring (C) of known resistance.The piston then activates the microswitch (A),which moves between the normally closed (NC) and normally open (NO) positions via the operating pin (B) and the isolation trip button (E).

Applications

Pressure switches are widely used in household and commercial applications as listed belowHVAC,gas cylinders,air pumps,etc.use air compressor pressure switches to monitor and control system air pressure.An oil pressure switch is used in the engine as an actuator or sensor to determine when the engine oil pressure drops below a preset level.Furnace pressure switch as a safety device for industrial and residential use.They detect negative pressure during furnace startup and shut down the furnace when the air pressure is low.Well pump pressure switches are used in understanding and commercial buildings to draw water from a well and ensure that the is is the sufficient water pressure in system to delivery water without overpressure.Water pump pressure switches for automatic regulatory of water flow in understanding,commercial and agricultural applications.Vacuum pressure switches measure vacuum or negative pressure in a system.They are used in residential boilers,electric heaters,air compressors and transmission systems.