Flow control switch

 Flow control
Flow switch & sensor & meter is used to control and monitor the flow of water, oil, air, gas and other medium.

Flow Switch is a mechanical switch that is switched on or off in response to the flow or non-flow of a fluid such as air or water. Flow switch might be used to protect a central heating system electric heating element from being energized before the air flow from the blower is established. And might also be used to alarm if a ventilation fan in a hazardous location fails and air flow has stopped.