Thought I'd post this in case someone else wants to detect flow. Reviews say it requires 4 gpm to close the contacts.
I have a 24vac solenoid on a water-to-air heatpump that is a pain to adjust for full shut-off. I need to monitor it on occasion to be sure it isn't beating the deepwell pump to death. I wired a contact sensor to the above paddle switch downstream of the solenoid and added another contact sensor to read discharge water temp near the cupronickel coil. Between the two, I can get an idea if the flow is right.