Most construction machinery is powered by diesel engines. Due to harsh operating environments, dust or rain and snow can easily enter the fuel tank and contaminate the diesel. In addition, long-term contact between the diesel and air in the tank and the inner wall of the tank will gradually produce some dirt that settles to the bottom or adheres to the tank wall. These factors will cause abnormal wear of the precision parts of the fuel system. Therefore, the fuel tank should be cleaned once every 600 hours of diesel engine operation.
The fuel tanks on construction machinery are tall, large and heavy, so it is impossible to remove them frequently for cleaning. However, for some construction machinery, such as rotary drilling rigs, which have very strict requirements for diesel cleanliness, many operators have no choice but to drain the remaining oil in the fuel tank, add clean diesel, and then open the drain switch until the flowing diesel contains no dirt. This method of cleaning the fuel tank is both wasteful and unable to clean the deposits on the inner wall of the tank thoroughly. For this reason, we recommend making a spray pipe that uses compressed air to clean the fuel tank. The spray pipe is a thin steel pipe 1 m long, with the bottom end plugged, and several small holes 1 mm in diameter drilled around the lower end. Using this spray pipe, there is no need to remove the fuel tank, and the interior of the fuel tank can be flushed clean in a few minutes.
1. Cleaning method
(1) Open the fuel tank drain switch and drain all remaining oil, then close both the drain switch and the fuel supply switch. Remove the fuel tank cap, filter screen and dipstick, and pour 20–40 L of clean diesel into the fuel tank as cleaning oil (depending on the tank capacity).
(2) Connect the air pump hose to the spray pipe, and insert the lower part of the spray pipe deep into the bottom of the fuel tank. When the air pressure in the air pump receiver rises to 0.6–0.7 MPa, open the gate valve so that the high-speed air flow rushes from the spray holes into the oil layer at the bottom of the fuel tank, causing the diesel to surge and splash, thereby flushing the interior of the fuel tank clean. During cleaning, the air pressure in the receiver should be maintained at 0.4–0.5 MPa. To prevent oil mist from spraying out of the fuel tank, plug the tank opening with gauze, but do not affect the left-right swinging of the spray pipe.
(3) Close the gate valve of the receiver, take out the spray pipe, drain all the cleaning oil from the fuel tank, add another 15–30 L of clean diesel, and clean once more according to the above method. After cleaning, drain the cleaning oil, install the filter screen, dipstick and fuel tank cap, and the fuel tank cleaning work is completed. The drained cleaning oil can be used for cleaning other fuel tanks or components after settling.
The above cleaning method can only be used for diesel fuel tanks and must not be used for gasoline tanks. This is because friction between compressed air and the tank wall can generate static electricity, and gasoline is flammable and explosive. Even under severe cold conditions of -30°C, a tiny spark can ignite gasoline and cause a safety accident.
2. Precautions for cleaning diesel fuel tanks:
(1) Diesel should be settled for more than 48 hours before being added to the fuel tank.
(2) Before work in each shift, open the fuel tank drain switch to drain the sediment at the bottom of the tank.
(3) During operation, pay attention to the amount of oil remaining in the fuel tank to avoid air entering the fuel system when the oil is used up, which would affect the normal operation of the machine.
(4) After work each day, fill the tank with diesel to prevent water droplets condensed on the inner wall of an empty tank from sinking into the diesel and causing premature corrosion of the precision parts of the fuel system.
(5) The vent hole in the fuel tank cap should be cleaned frequently to prevent negative pressure in the fuel tank, which would reduce fuel delivery pressure and fuel supply, causing reduced machine power or unstable operation.