Flow switches are devices used to monitor the flow of liquids, gases, or steam in pipelines and systems. They detect the presence or absence of flow and trigger an action, such as activating an alarm, controlling a valve, or shutting down equipment, based on predefined flow conditions. There are several types of flow switches, each with its own principle of operation and applications:

1. Paddle Flow Switches:

   • Principle of Operation: Paddle flow switches have a paddle or vane that extends 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.
   • Applications: Paddle flow switches are commonly used for pump protection, low flow detection, equipment safety, and process control in applications with relatively low flow rates and clean fluids.

2. Piston-Operated Flow Switches:

   • Principle of Operation: Piston-operated flow switches use 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.
   • Applications: Piston-operated flow switches are suitable for applications with moderate to high flow rates and are used for pump protection, flow monitoring, and process control in industrial process systems.

3. Vortex Shedding Flow Switches:

   • Principle of Operation: 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, triggering a switch to indicate flow.
   • Applications: Vortex shedding flow switches are used in applications with relatively high flow rates for pump protection, flow monitoring, and process control in industries such as water treatment, HVAC, and chemical processing.

4. Magnetic Flow Switches:

   • Principle of Operation: 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.
   • Applications: Magnetic flow switches are often used for flow monitoring, pump protection, and process control in applications with conductive fluids such as water, wastewater, and chemicals.

5. Thermal Flow Switches:

   • Principle of Operation: 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.
   • Applications: Thermal flow switches are used in applications with low flow rates for pump protection, flow monitoring, and process control in HVAC systems, process heating, and cooling applications.

These are some of the main types of flow switches and their 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.