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Flow Switch

Understanding The Flow Switch

The flow switch is designed to monitor the flow of air, liquid or steam. The device transmits a trip signal through to another device in the system, called a pump. Flow switches are typically built to indicate to the pump regarding shutting off or to turn on. A flow switch has several different uses. Some of the uses of flow switches include cooling-circuit protection, pump protection, and alarms for too high or very low flow rates. Below is more information about this device.

What is it Used For?

A flow switch is uniquely built to perform specific functions according to the needs of the operator. Take an example; flow switches can stop a motor if there is no flow present. It can start a motor once a flow is present. It can sound an alarm whenever the flow stops or even shut off the alarm whenever the flow is appropriate or in line.

Liquid flow switches can also be used for air conditioning, pump systems, blending or additive systems, hot water space heating systems, water-cooled equipment, liquid transfer systems, water treatment systems, fire sprinkler systems, industrial laser coolant and swimming pool chlorination systems. Additionally, flow switches are used to power clean room filter systems, exhaust ventilating, duct type heating, air supply, and treatment systems.

What is The Definition of Flow?

Flow means the physical movement (or velocity) of gas, liquid, or steam inside a pipe that makes a switch to actuate. When there is a no-flow, this means a complete stoppage or a decrease in velocity that allows the switch to go back to its original position.

What are The Types of Flow Switches Available?

There are several different kinds of flow switches available. The vane-operated air switch utilizes the fluid that is pushing against the paddle in a liquid flow. When the current drops under the pre-set levels, it will trigger, a mechanical swim actuation lever and an internal magnetic coupling which trips the switch. The variable area liquid switch uses several modes to activate the switch and has an internal piston. The flow comes through a port, forcing pressure against a poppet.

Additionally, when the flow pressure achieves a set level, the switch will close. A high pressure switch is attached or joined to the outer side of the pipe. This device uses ultrasonic sensors to transmit ultrasonic signals when there is a change in flow detected. Finally, a thermal dispersion switch is a probe designed for measuring the difference between the temperature of the gas or liquid as its passes detecting elements and triggering a signal when there is a change.

Other Considerations

Measuring the flow rate in liquid flow is inferred by calculating liquid velocity or change in kinetic energy. The speed will depend on the pressure differential forcing the liquid through the pipe or conduit. Additionally, because the cross-sectional area of the tube is known and stays constant, the average velocity can be an indication of flow rate. Flow rate can be determined to set flow switch to a pre-determined close function.


Harwil Corp.
(805) 988-6800
Flow Switch
541 Kinetic Dr
Oxnard CA 93030 US

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