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Inst Tools > Blog > Flow Measurement > Flow Switch : What is it? – Applications

Flow Switch : What is it? – Applications

Flow Switch is a mechanical device that is switched on or off in response to the flow or non-flow of a fluid such as air or water.

Last updated: November 2, 2023 10:37 am
Editorial Staff
Flow Measurement Switches
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A flow Switch is a mechanical switch that is switched on or off in response to the flow or non-flow of a fluid such as air or water.

Contents
Flow SwitchWhy does the Flow Switch Show the wrong indication?Applications of Flow Switch

The flow switch typically operates through the use of a paddle which gets displaced due to the force of fluid moving past it.

Flow Switch

Flow Switch Working
Image Credits: omega

The flow switch consists of a paddle system (1) which has a permanent magnet (2) located at its upper end. A reed contact (3) is positioned outside the flow above this magnet. A second, magnet (4) with opposite polarity is used to create a reset force.

The paddle system is moved once it comes into contact with the flow which is to be monitored. The magnet (2) changes its position in relation to the reed switch contact (3). The contact opens/closes depending on the contact type.

As soon as the flow is interrupted, the paddle returns to its original position, and the reed switch contact opens/closes depending on the contact type. This change in contact (NO to NC or NC to NO) will be used to indicate the required flow signal output.

Flow Switch Principle

Flow switch is a special electric device with a very simple design and of a small size. But despite its simplicity, flow switch plays an important role in the variety of different applications.

These devices are used with the purpose of protecting a pump and when the flow of air, gas, or liquid through the specific line needs to be monitored.

Also, the alarms can be triggered with the help of them when it is necessary. Switches may be specific to a type of application.

Also Read: Identify Two Pressure Switches Logic

Why does the Flow Switch Show the wrong indication?

Below are the possible causes for the false activation of the flow switch :

  • Entrapped air or gas.
  • Turbulence in tubing or unit
  • Mechanical sensor assembly damaged.
  • Liquid is too viscous.
  • Not using the fittings supplied by the manufacturer.
Water Flow Switch Principle

Applications of Flow Switch

These switches find application in the detection of fluid flow and measurement of fan speeds.

A flow switch might be used to protect a central heating system electric heating element from being energized before the airflow from the blower is established.

Flow switches might also be used to alarm if a ventilation fan in a hazardous location fails and air flow has stopped.

  • Pump protection
  • Safety spray nozzle monitoring
  • Cooling water or heat exchangers
  • Oil well system testing
  • Drain line flow
  • Relief valve monitoring

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Read Next:

  • Types of Flow Meters
  • Rotary Abutment Flow Meter
  • Image Velocimetry Principle
  • Positive Displacement meter
  • Microwave Flow Sensor Principle
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5 Comments
  • Qadir Mohtasham says:
    November 7, 2018 at 1:59 pm

    Great

    Reply
  • aravind says:
    November 11, 2018 at 7:25 pm

    sir i need PDF of this how can i get

    Reply
  • myo thant kyaw says:
    March 3, 2019 at 12:50 am

    i can not find about Vaccum swich which is used in fixed gas detection system for leakage test.

    Reply
  • joby john says:
    September 26, 2019 at 3:34 pm

    can we mount paddle type flow switch vertically

    Reply
  • Naman Modi says:
    November 28, 2020 at 9:38 am

    Excellent article on flow switch, I learned a lot of information. Flow switch we can also operate with pump. How flow switch plays a different role?

    Reply

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