A flow switch is a mechanical switch that is switched on or off in response to the presence or absence of flow of fluid through it. Reed Switches are used in flow switches to detect a set value of flow. Flow Switches can be manufactured to either operate in a normally-closed or a normally-open form.
A sail switch, vane switch or flow switch is a mechanical switch that is actuated on or off in response to the flow or non-flow of a fluid such as air or water. A sail switch typically operates through the use of a paddle or a diaphragm which gets displaced due to the force of fluid or air moving past it. Sail switches find application in the detection of fluid flow and measurement of fan speeds. A sail switch might be used to protect a fan forced pellet stove, central heating system, electric heating element from being energized before the air flow from the blower is established. Sail switches might also be used to alarm if a ventilation fan in a hazardous location fails and air flow has stopped. For some HVAC systems, a sail switch can activate an electronic air cleaner, a humidifier, or other equipment in response to airflow from the system fan.