A Direction of travel
1 Fuel return to fuel tank
2 Manual pump
3 Hand pump bypass line
4 Fuel feed line to high pressure pump
5 Fuel return line from high pressure pump
6 Fuel feed line from fuel tank
Some versions with Siemens common rail system are equipped with a rubber hand pump. This is for bleeding the fuel pipes prior to initial operation of the vehicle or may be used during repair work.
With the hand pump, fuel can be pumped from the fuel tank via the fuel filter to immediately before the high pressure pump port.
Due to the installation position of the hand pump in the bypass line between the fuel feed and return lines, the normal flow of fuel through the high pressure pump is bypassed.
This arrangement prevents the hand pump from interfering with the normal fuel flow through the high pressure pump. It also ensures that the fuel can be extracted as close to the high pressure pump port as possible when bleeding the system following repair or maintenance work.
For vehicles that are not equipped with a hand pump, the special tool for bleeding the system must be used.