2 Inch Flow Switch Model 210 57-F1-2212-01W - Water Flow Sensor for HVAC, Plumbing & Industrial Applications

I used this to ensure my salt water chlorine generator did not have power if there was no water flowing as an extra safety measure after adding a variable-speed pump to my pool. I already had a couple of these on my pool heater. It works great and is very reliable. The price here was the best I could find, and it was delivered quickly and in perfect condition.