What is a flow switch

The flow switch is a device designedto control the flow of air, gas or liquid. It sends a control signal to another device in the system, serving, for example, to stop the operating mechanisms. In particular, the flow switch can control the switching on and off of pumps. Some of the common relay applications are designed to protect pumps, to control cooling systems and signaling the deviation of the flow rate from a given level.

As an example,a liquid flow and gas flow switch produced by McDonnell & Miller. Water flow switches, for example, can be used for air conditioning, in devices for heating water in water cooling systems of equipment, in fire extinguishing systems, in water purification systems, chlorination of pools, etc.

Switches controlling airflow can be used for ventilation of premises, filtration system in heating mains, air supply, purification and treatment systems.

The concept of flow means physical movement(speed) of the liquid, gas or vapor in the pipe, which drives the flow switch. The absence of a flow means a decrease in its velocity to zero; until it stops completely, allowing the switch to return to its original position.

To set a certain thresholdthe flow switch (setpoint), the speed must be preset in accordance with the application conditions. For example, the relay can stop the engine if there is no flow, start it, if the duct is present, give a sound in the event of a flow stop, or turn off the alarm if the indicator returns to normal.

There are several different types of flow switch, the most common of which is a turbine-type instrument.

Turbine flowmeters are indispensable in common industrial applications for liquids and gases. They combine excellent performance with quality and reliability.

The fluid entering into engagement with the rotor blades of the blade turbine located in the flow path causes its rotation with an angular velocity proportional to the flow velocity.

Rotating inside the pipe rotor, usinga special device, converts the flow rate into a pulsed electrical signal. The total impulse electrical signal is directly connected to the total flow in such a way that its frequency is directly proportional to the flow velocity of the liquid (gas) flowing through the flow switch. This signal is processed by an electronic circuit, which eventually forms the output circuit of the flow switch in the form of a mechanical contact.

Turbine switches are used fordetection of fluid flow and measurement of fan speed. They can also be used to protect the heating system with electrical heating elements, regulating the intensity of the airflow coming from the fan. Turbine air flow switches can also be used to provide an alarm, in case of inefficient operation or a complete stop of the fan.

In addition to this common type of flow switch,there are many others, differing in the arrangement of the mechanism and the principle of action. The choice of the manufacturer and the type of device depends on the application conditions and the requirements for its technical characteristics in each particular case.