Fuel Pressure Regulator: Description and Operation

Fuel Pressure Regulator:

CONSTRUCTION
Regulator is a diaphragm-controlled overflow type, which maintains fuel pressure at a constant 43.5 lb sq in (3bar), above pressure in intake manifold. It consists of a metal housing divided into two chambers by a diaphragm: a spring chamber for pre-stressed helical spring which rests on diaphragm and a chamber for fuel.

Fuel Pressure Regulator:

OPERATION
System uses one pressure regulator fitted to fuel rail. When fuel pump exceeds set system pressure, valve controlled by diaphragm, opens inlet to fuel return line, where excess fuel can flow back to fuel tank without pressure. A vacuum line connects spring chamber of pressure regulator and intake manifold. This line receives its vacuum from behind throttle valve.

This results in fuel system pressure being dependent on absolute pressure in intake manifold and therefore maintaining a constant pressure drop over injectors, no matter what throttle valve position is. This means that fuel quantity injected depends only on time injectors are open (injection duration). When engine is turned OFF, pressure regulator will maintain a rest pressure.