Fuel Pressure Regulator: Description and Operation

Fig. 3 Cross sectional view of fuel pressure regulator:

The fuel pressure regulator, Fig. 3, holds fuel system pressure at a constant preset value of 36 psi. The regulator receives manifold vacuum through a hose connected to the intake manifold, enabling the difference between intake manifold pressure and fuel pressure to be held constant. The drop in fuel pressure across the fuel injectors is constant for all load conditions, therefore the connection to manifold vacuum is necessary to maintain correct fuel flow to the injectors during all operating conditions. Since less fuel is required at idle, and more is required during high engine speeds and loads, the pressure regulator maintains the correct fuel flow by controlling the amount of fuel returned to the fuel tank.
The regulator contains a diaphragm and calibrated compression spring. The lower side of the diaphragm is influenced by fuel pressure, while the upper side is influenced by manifold vacuum. The compression spring is constantly working to keep the outlet to the fuel return line closed. However, the combination of fuel pressure and manifold vacuum act in unison against spring pressure to open the fuel outlet as required.