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Flow Switches- Types and Their Working Processes

A flow switch, also known as a sail switch, flow indicator, or flow sensor, is a device mechanically made to respond to a liquid, gas, or steam flow, non-flow rate, or pressure where it sends a trip sign to pumps or pipes to protect them. System operators also use these switches to activate an alarm, on or off, to ensure the protection of the machine or system whenever there is a need. Here, we explain different types of flow switches with their working procedure.

How does a flow switch work?

A flow switch contains a paddle magnet, which connects the circuit at the flow channel where liquids, steam, or gasses are passing through. The substance flowing displaces the paddle sending a signal to the transducer, a secondary component of the system that further supplies it to the transmitter where one can read it.

The transmitter adjusts the working mechanism or the behavior of the parameters by measuring, recording the reading, and performing whatever the system requires, which is why flow switches are to monitor, control, and report the flow rate of various substances through a whole system or at the specific part of the system.
The flow switch performs different actions depending on its types. Some can shut off a motor or system, divert the flow, trigger an alarm, or power a pipe or pump. The flow switches that do not have paddles like ultrasonic work by bouncing a signal back at the monitoring media.

The flow switches which do not have paddle can be useful in areas where there is physically damaging, contamination of substances, dangerous occurrences, etc. The magnetic flow switches are usually effective, mainly in areas where there are conducive media.

The procedure of installing and testing a flow switch

Installing and testing a flow switch varies from type to type since various flow switches have different designs, specifications, and applications. Generally, to install and test a flow switch, one has to know what the flow switch is meant to do and how it is made. Below is a general rule that you can use to install and test most flow switches.

i) You should consider installing a flow switch on a straight line of the pipe, pump, or duct.
ii) Make sure that you have a straight pipe with a perfect length at the back and in front of the flow switch, usually a diameter of ten.
iii) Do not wire a flow switch near valves, drains, bends, wider, or narrow areas since it can destroy the flow rate at the channel.

To test a flow switch, you should observe and record the reading immediately after the flow of any substance starts or stops. By doing this, you will be able to know whether the results are correct or not. If you notice any interruption of the flow switch, then you should do some repair for it.

Types of flow switches

1. Liquid flow switches

Liquid flow switches are switches that monitor the flow rate of chemicals, lubricants, slurries, and water which is why many industrial applications use them. These kinds of flow switches are easy to use and their results will be reflected.

2. Velocity flow switches

Velocity flow switches are switches that system operators use to monitor and measure the flow rate of a moving media in velocity per minute time.

3. Gas flow switches

These are flow switches that industrial operators use in HVAC applications to measure the flow rate of steam or air.

4. Volumetric flow switches

Volumetric flow switches are switches that control and measure the flow rate of gases or liquids in volume per minute time.

The types of flow switches can be further categorized depending on the specific functions they do. We shall discuss some of the operations with each type.

1. Air or Gas flow switches

These are flow switches designed in a non-intrusive or mechanical way to measure or control the flow rate of duct heating, air filtration, or exhaust venting. Some of the examples of the uses of gas and air flow switches are;

i) Airflow switch for boilers

The airflow switch for boilers designed to allow the switching on only at a considerable speed where they monitor the right flow of waste gases using fans from the system and through the flue. The air and gas flow switch can also detect when there is any problem stopping the boiler switch from lighting up for the operator to fix it.

ii) Airflow switch HVAC and ducting

In HVAC and ducting systems, operators use an airflow switch to activate the micro-switch in case of a decrease or increase in the volume of the flow rate. They also monitor fans, filters and handle air substances.

iii) Inline airflow switches

These types of flow switches are difficult to insult and maintain since one has to ensure that there is proper feeding at an integral part of the duct. However, many industries commonly use inline flow switches due to their multi-functioning ability for a longer time. It can be used in homes, a small type of industry. 

iv) Paddle airflow switches

Air and gas being monitored in the duct displace the paddle switch directly into the channel, which activates the decrease or increase of the flow at a specified rate in the channel, which is why it is known to partly protrude in the measuring channel. The best flow device available at a cheap cost. 

2. Water and fluids flow switches

Water flow switches operate by the use of a physical paddle or ultrasonic where the paddle rotates and shows the flow rate to the transducer, which supplies the information to the transmitter to be recorded as an action signal.

Some of the types of water and fluid switches are;

i) Sprinklers’ flow switches.
ii) Water pumps flow switches.
iii) Paddle water flow switches.
iv) Inline water flow switches.

3. Flow switches for oil

Oil flow switches operate at higher temperatures and pressures since they are more hard-wearing as compared to other flow switches. They measure the flow rate of oils or fuels in industrial engines or motors.

4. Mechanical flow switches

Mechanical flow switches are flow switches that contain many parts that get activated by the direct contact of the controlled media.

5. Flow switches for thermal dispersion

It designs such that there is no moving part on it, and it controls the flow rate of heated liquids or gases passing through a pipe or channel.

Applications of flow switches

1. A flow switch uses to keep the water tanks at a designated level in storage systems and reservoirs.
2. Flow switches use to detect any leakage or blockage in pipes.
3. System operators use flow switches to protect the flow and the operating system since they can shut off in case of any danger or send a signal to the operator to fix the problem.
4. A flow switch can use in staging and failure of the pipe or pump.


flow switch is an essential device in industries, homes, commercial setups, or big buildings since it measures, monitors records, and sends a trip signal to other devices like pipes or pumps, thus ensuring their full protection in case of any dangerous occurrence. One should choose a flow switch depending on the type of application.

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