We went with an AODD pump in the pit, stainless with flap valves, and a dampener on the line. The separator is happy. On the screen I used the Diaphragm pump from the Process library, bound Running to pump_running (from a pressure switch on the air line) and it animates. Laura, I called the symbol p1 and renamed the key to p1.running after reading your last line, it connected by itself.
Modbus is just registers until it isn't.