Along with the electric fuel pump, fuel filter, injection valves, and pressure regulator, the fuel rail forms part of the fuel supply system which always supplies the engine with the necessary amount of fuel under all operating conditions. The pressure generated by the fuel pump is applied to all injection valves by way of the fuel rail. The unused fuel flows back to the fuel tank via a pressure regulator. In most cases, the pressure regulator (fuel rail – conventional design with pressure regulator) uses the intake manifold pressure as a reference. The use of this typical pressure and the flow through the fuel rail (fuel cooling) prevent the formation of any unwanted vapor bubbles in the fuel.