Fuel Pressure Regulator
Fuel pressure regulator is a diaphragm-operated relief valve with injector pressure on one side and manifold pressure on the other. See Fig 1. Pressure regulator compensates for engine load by increasing fuel pressure when low manifold vacuum is experienced.
Fuel pressure is regulated when pump pressure acting on the bottom side of the diaphragm overcomes the spring force action on the top side. Diaphragm movement opens or closes the fuel chamber orifice, controlling the amount of returned fuel which maintains constant pressure at the injectors.