Nowadays, most cars have a fuel return pipe. When the fuel pump supplies fuel to the engine, a certain pressure is formed. In addition to the normal supply of fuel nozzles, the remaining fuel is sent back to the fuel tank through the return pipe, and of course there is excess gasoline collected by the carbon canister. The steam also returns to the fuel tank through the return pipe to return excess oil to the fuel tank, which can relieve the pressure of gasoline and reduce fuel consumption.
When the fuel pressure provided by the fuel transfer pump exceeds 100 to 150 kPa, the overflow valve in the return line of the fuel filter opens, and the excess fuel flows back to the fuel tank through the return line.
Since the fuel delivery volume of the fuel delivery pump is 2 to 3 times the maximum fuel delivery volume under the calibrated conditions of the fuel injection pump, the excess fuel will flow back to the fuel tank through the fuel return pipe.
When the fuel injector is working, there will be a very small amount of fuel leaking from the mating surface of the needle valve and the needle valve body, which can play a lubricating effect, so as to avoid excessive accumulation and cause the needle valve back pressure to be too high and malfunction. This part of the fuel is introduced into the fuel filter or fuel tank through the hollow bolt and return pipe.