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, which serves, for example, to stop working mechanisms. In particular, a flow switch can control the on and off of pumps. Some of the general applications of relays are designed to protect pumps, to control cooling systems and to signal the deviation of the flow rate from a given level.
As an example, the fluid and gas flow switches shown by McDonnell & Miller are shown in the figure. Water flow relays, for example, can be used for air conditioning, in devices for heating water in equipment water cooling systems, in fire extinguishing systems, in water purification systems, pool chlorination, etc.
Switches that control the air flow can be used for ventilation, filtration systems in heating mains, air supply, purification and treatment systems.
The concept of flow means the physical movement (speed) of a liquid, gas, or vapor in a pipe that drives a flow switch. The absence of a duct means a decrease in its velocity to zero, i.e. until it stops completely, allowing the switch to return to its original position.
To set a specific threshold for the flow switch (setpoint), the speed must be pre-set depending on the application. For example, in the absence of a duct, a relay can stop the engine, start it if a duct is present, give a sound in case of a duct shutdown, or turn off an alarm if the indicator returns to normal.
There are several different types of flow switches, the most common of which is a turbine type device.
Turbine flow meters are indispensable in general industrial applications for liquids and gases. They combine excellent performance with quality and reliability.
The fluid, engaging with the blades of the rotor of a blade impeller located in the path of flow, causes its rotation with an angular velocity proportional to the flow velocity.
A rotor rotating inside the pipe, using a special device, converts the flow rate into a pulsed electrical signal. The total pulsed electrical signal is directly connected to the total flow in such a way that its frequency is directly proportional to the velocity of the fluid (gas) flowing through the flow switch. This signal is processed by an electronic circuit, which ultimately forms the output circuit of the flow switch in the form of a mechanical contact.
Turbine switches are used to detect fluid flow and measure fan speed. They can also be used to protect a heating system with electric heating elements by adjusting the intensity of the air flow coming from the fan. Turbine air flow switches can also be used to signal 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 arrangement of the mechanism and the principle of operation. The choice of the manufacturer and the type of device depends on the conditions of use and the requirements for its technical characteristics in each case.