The fuel pressure regulator is a diaphragm operated pressure relief valve. To maintain precise fuel metering, the fuel pressure regulator maintains a constant pressure differential across the fuel injector. This means that the pressure in the fuel rail will always be at a constant value above manifold absolute pressure.
The specified pressure differential is either 36 PSI (2.55 kg/CM2) or 41 PSI (2.90 kg/CM2) depending on engine application.* Maintenance of this pressure differential is accomplished by balancing a spring, assisted by manifold pressure, against a diaphragm which holds a ball valve on its seat.
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