When the pressure of the fluid at port 1 exceeds the preset value, plunger 2 is raised, compressing a spring whose tension is adjusted by threaded member 3, and surplus fluid drains through a hole in the plunger and port 4 to the tank. Raised together with the plunger is pusher rod 5, linked to the plunger, which automatically switches the pump drive motor on or off.
$3764$SHP,Re$