A flow switch is a device designed to control the flow of air, gas or liquid. It sends a control signal to another device in the system, serving, for example, to stop running mechanisms. In particular, the flow switch can control the activation and deactivation of pumps. Some of the common applications of relays are for pump protection, for controlling cooling systems, and for signaling flow rate deviations from a predetermined level.
The liquid and gas flow switches shown in the figure, manufactured by McDonnell & Miller, can serve as an example. Water flow switches, for example, can be used in air conditioning, water heating devices, cooling water systems, fire extinguishing systems, water treatment systems, pool chlorination, etc.
Switches that control the air flow can be used for room ventilation, filtration systems in heating mains, air supply, purification and treatment systems.
The concept of flow means the physical movement (velocity) of a liquid, gas or vapor in a pipe, which actuates the flow switch. No ductmeans a decrease in its speed to zero, i.e. to a complete stop, allowing the switch to return to its original position.
To set a specific flow switch threshold (setpoint), the speed must be pre-set depending on the application conditions. For example, the relay can stop the engine if there is no flow, start it if there is flow, sound if the flow is interrupted, or turn off the alarm if the indicator returns to normal.
There are several different types of flow switch, the most common being the turbine type.
Turbine meters are indispensable in general industrial applications for liquids and gases. They combine excellent performance with quality and reliability.
The fluid medium, engaging with the rotor blades of a bladed turbine located in the path of the flow, causes it to rotate with an angular velocity proportional to the flow velocity.
The rotor rotating inside the pipe, with the help of a special device, converts the flow rate into a pulsed electrical signal. The total pulsed electrical signal is directly related to the total flow in such a way that its frequency is directly proportional to the flow rate of the liquid (gas) flowing through the flow switch. This signal is processed by the electronic circuit, which eventually forms the output circuit of the flow switch in the form of a mechanical contact.
Turbine switches are used forfluid flow detection and fan speed measurement. They can also be used to protect a heating system with electric heating elements by regulating the intensity of the airflow coming from the fan. Turbine flow switches can also be used to give 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 that differ in the mechanism and principle of operation. The choice of manufacturer and type of device depends on the conditions of use and the requirements for its technical characteristics in each particular case.
