How to Select a Flow Switch for Liquids


Gems Sensors manufactures Flow Switches that can be used to detect liquid flow.  These flow switches can indicate when a system has lost flow or has too much flow.  Most common is a loss of flow as coolant flow is crucial for many applications to prevent equipment from overheating.  Flow switches will not indicate the actual flow rate, they will only indicate when flow has reached the setpoint.  If your application requires you to know the flow rate, then you will need a flow sensor like Gems Rotor Flow or Gems Flow Turbines. 


First step is to review the average flow rate in your system, which will then determine what flow setpoint you need.  The flow setpoint will typically be at least 25% less than the low end of your flow rate.  It’s important to not select a setpoint too close to the normal flow rate as you could receive nuisance trips.  You also want to make sure your setpoint is not low enough that the flow rate will not damage your equipment even before the flow switch setpoint.  Also, flow switches may have a 10-20% accuracy, so make sure that tolerance does not cause your setpoint to fall within your normal flow rate. 


For example, a flow setpoint of 1 GPM with a 20% accuracy may switch as low as .8 GPM and as high as 1.2 GPM. 


Gems Flow Switches have setpoints down to 50 ml/min and up to 50 gal/min. 


Gems utilizes four basic operating principles, piston, shuttle, paddle, and electronic.  Review each operating principle to determine which suits your application the best. 





Electronic flow switch uses thermal dispersion which provides a no moving parts flow switch that requires little to no filtration.  With port sizes ranging from ½” up to 1 ½ ” NPT.  


Piston flow switches allow for small, compact housings with port sizes down to ¼" NPT and are accurate and reliable. 



Shuttle type flow switches have port sizes from ¾" NPT up to 2” NPT which allow for even viscous liquids and low pressure drop even at full flow. 




Paddle type flow switches can handle pressures up to 2000 PSI and its unique cam design assures low pressure drop and can be placed in pipes up to 10” in diameter.


Next step is to review the wetted components and body material to make sure they are compatible with the liquid.


Review the full line of Gems Flow Switches by clicking here.