What is actually happening is the grease is being primed to a high pressure inside a chamber. When this chamber pressure is high, the circuit switches the motor off. As a machine gets greased, the pressure inside this chamber will drop causing the motor to kick back on.
does that answer your question? Or have i overlooked something major..
Yes, but as I described in my last post, that's not what Harold's or my circuit does. I don't see a timer in your reply. Considering your description It would seem more logical that a pressure switch should be turning the motor off @ 500PSI and turning it back on at some predetermined lower pressure.