Flow switches are devices used to detect the presence or absence of flow in a pipeline or system. They are typically installed in fluid handling systems to monitor flow conditions and trigger an action based on predefined flow criteria. Flow switches are commonly used for flow control, pump protection, equipment safety, and process automation. Here are the types of flow switches:

1. Paddle Flow Switches: Paddle flow switches consist of a paddle or vane inserted into the flow stream. When fluid flow exceeds a certain threshold, the flow velocity pushes the paddle, causing it to pivot or rotate. This movement actuates a switch mechanism, signaling the presence of flow. Paddle flow switches are often used in applications with relatively low flow rates and clean fluids.

2. Piston-Operated Flow Switches: Piston-operated flow switches utilize a piston or shuttle mechanism that moves in response to fluid flow. When flow reaches a predefined level, the piston is displaced, triggering a switch to indicate flow presence. Piston-operated flow switches are suitable for applications with moderate to high flow rates and are often used in industrial process systems.

3. Vortex Shedding Flow Switches: Vortex shedding flow switches detect flow based on the vortex shedding principle. They feature a bluff body or shedder bar positioned in the flow stream. As fluid flows past the bluff body, alternating vortices are shed on either side, causing the bluff body to oscillate. This oscillation is detected by a sensor, which triggers a switch to indicate flow. Vortex shedding flow switches are used in applications with relatively high flow rates and are suitable for both liquids and gases.

4. Magnetic Flow Switches: Magnetic flow switches utilize magnetic field disruption to detect flow. They consist of a magnetic sensor and a target or flow sensor element placed in the flow stream. When fluid flow moves the target, it disrupts the magnetic field, which is detected by the sensor, triggering a switch. Magnetic flow switches are often used in applications with conductive fluids, such as water and chemicals.

5. Thermal Flow Switches: Thermal flow switches operate based on the principle of heat transfer. They use a thermal sensor or probe inserted into the flow stream. When fluid flow passes over the sensor, it absorbs or dissipates heat, causing a change in temperature. This change in temperature is detected by the sensor, triggering a switch to indicate flow presence. Thermal flow switches are suitable for applications with low flow rates and are often used in HVAC systems, process heating, and cooling applications.

These are the main types of flow switches commonly used in industrial and commercial applications. The selection of a flow switch depends on factors such as flow rate, fluid type, temperature, pressure, and the specific requirements of the application.