Detecting when water flow stops

Flowmeters are used to measure liquid flow. However, if you only need a notification that flow is present or not and don’t need to know the quantity of liquid, there are simpler methods.

A flow switch is an on/off device that will indicate whether or not a liquid is moving. They can be either Normally Open (NO), meaning that the switch is not conducting when there is no flow, or Normally Closed (NC) meaning that the switch is conducting when there is no flow. Having both types available offers flexibility to a design. One of the nice things about a flow switch is that is is very simple to build a visual indicator of whether the liquid is flowing or not. By using a light (bulb or LED) or a buzzer and a flow switch you can build a simple low flow alarm.

They are available in various pressure ratings that set the threshold of flow/no flow.

Flow switches generally present less resistance to flow than a flow meter, so there is less pressure loss across the switch.

As with flowmeters, our PRT232 is an easy way to read a flow switch and get an indication of fluid flow into your PC via an RS232 serial connection.