1. Under normal circumstances, the fuel inlet pipe is above the fuel injector.

2. The oil return pipe is below and branched from the inside of the zhi and the oil inlet pipe.

3. Generally larger than the oil return pipe. The oil inlet pipe is the one connected to the fuel filter element.

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.

The diesel engine fuel supply system is generally equipped with three return lines, and some diesel engine fuel supply systems have only two return lines, but there is no return line from the fuel filter to the fuel tank.

Oil return line on fuel filter
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.

Oil return line on fuel injection pump
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.

Oil return line on the injector
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.

In order to overcome the resistance of fuel flowing in the low-pressure oil circuit and ensure the fuel supply to the fuel injection pump and the fuel injector, diesel engines have certain requirements on the fuel pressure supplied by the fuel delivery pump. The two ends of the low pressure chamber above the plunger fuel injection pump body used in most multi-cylinder diesel engines are respectively provided with an oil inlet pipe street and an oil return joint, and an overflow valve is installed in the oil return joint.

When the fuel pressure in the low pressure and strong pressure in the fuel injection pump body is lower than 50~60 kPa, the overflow valve is closed and there is no fuel flow in the fuel injection pump return pipe; when the fuel pressure in the low pressure chamber in the fuel injection pump body is higher than 50~60 kPa When the time, the overflow valve is opened, so that part of the fuel flows back to the fuel tank or the fuel inlet port of the primary fuel filter through the return line and the return line of the fuel injector, so that the low pressure chamber in the fuel injection pump body maintains the specified oil pressure. This is the case with the return pipe on the fuel injector.

From the design point of view, the quantity of fuel delivered by the fuel transfer pump cannot meet the quantitative requirement, and the required quantity of the fuel injection pump is generally exceeded. Furthermore, although the needle valve assembly of the injector is very precise, in order to ensure fuel injection, there is still a slight matching gap. When the injector is working, the needle valve and the needle valve body are between the needle valve body and the upper end surface of the needle valve body. Fuel leakage is unavoidable between the lower ends of the injector body.

Once the fuel accumulates in the inner cavity of the injector, when the oil pressure reaches a certain level, it will cause difficulty in raising the needle valve, irregular fuel injection or even jam the needle valve. After the oil return pipe is set and the excess fuel is discharged, the above-mentioned undesirable phenomena can be eliminated to ensure the normal operation of the diesel engine.