Fuel Pressure Regulator: Description and Operation

Fig. 18 Fuel pressure regulator:

The pressure regulator controls the pressure of fuel so a pressure difference of 36.3 psi can be maintained between the fuel pressure and intake vacuum. This constant differential pressure provides optimum fuel injection in every mode of engine operation.
When the intake manifold vacuum becomes great enough to overcome the diaphragm spring force as combined with the fuel pressure at the pressure line, the diaphragm becomes empty on the intake-side, Fig. 18. This opens the return-side port to allow fuel to flow to the tank for reducing fuel pressure.
If fuel pressure is higher than the intake manifold vacuum by 36.3 psi, the diaphragm returns to the original position by spring force and closes the return port.
The pressure regulator maintains the fuel pressure in the fuel line 36.3 psi higher than the pressure in the intake manifold.