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.[1] 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.[2] 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.[2] 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.[3]


  1. ^ Matthew J. Darr; et al. (2007). "A Robust Sensor for Monitoring the Operational Status of Agricultural Ventilation Fans". Transactions of the ASABE. 50 (3): 1019. doi:10.13031/2013.23142.
  2. ^ a b Steven J. Hoff; et al. (June 2009). "Real-Time Airflow Rate Measurements from Mechanically Ventilated Animal Buildings". Journal of the Air & Waste Management Association. 59 (6): 685. doi:10.3155/1047-3289.59.6.683. PMID 19603736. S2CID 46390769.
  3. ^ "Honeywell S688A1007 Sail Switch SPDT". Bel-Aire. Retrieved 20 December 2015.