Fuel Pressure Regulator
WARNING: This page is about a different car, the 2003 Suzuki Vitara. However, it is still accessible from the selected car via links, so may be relevant.
The fuel pressure regulator is diaphragm-operated relief valve consisting of diaphragm, spring and valve. It keeps the fuel pressure applied to the injector 290 kPa (2.9 kg/cm2 , 41.2 psi) higher than that in the intake manifold at all times.
The pressure applied to the chamber "A" of fuel pressure regulator is intake manifold pressure and that to the chamber "B" is fuel pressure.
When the fuel pressure rises more than 290 kPa (2.9 kg/cm2 , 41.2 psi) higher than the intake manifold pressure, the fuel pushes the valve in the regulator open and excess fuel returns to the fuel tank via the return line.