The pressure sensor will have two uses. Check that the pump is actually pumping and hasn’t lost prime. And check that the output pressure is not too much lower than normal (set points to be determined). Basic function that I am thinking of (set points subject to change) is:
Within 2 minutes of startup have pressure of at least 30 PSI. If not shutdown pump and send email notification.
If the pressure drops below 35 PSI send a warning email that the pressure is low so I know to clean the filter.
Unless I incorporate this into OS I will run the pump signal from OS to an input on Arduino. Then an output pin on Arduino will control the relay for the pump allowing shutoff of the pump independent of OS. Probably just an Arduino Uno that sends status messages to the PI over USB serial. Then a script on the Pi that can send emails (and possibly make API calls to OS). Not putting the Arduino directly on the network. I’ve done similar things like this before – it could probably be done in a more technically elegant way but this way is fairly simple and easy and gets the job done.
If I could do this in OS that would be great but I don’t want a major project.