Diesel Tanks and Lines

The fuel tank stores fuel in a convenient location, away from the engine. It is commonly made of steel or aluminum. Baffles are plates usually installed vertically in the fuel tank to control sloshing of the fuel. They also ensure that the pickup tube is always submerged in fuel, thereby stopping air from entering the system. The inside of the tank can be treated to prevent rust. Galvanizing must never be used, because diesel fuel reacts with zinc to produce powdery flakes that can block fuel filters.

Usually, in light commercial diesel engines, two fuel lines are used. One supplies, or transfers, the fuel from the tank to the filters, and then to the fuel injection pump. The other is the return line. It carries excess fuel back to the tank. The fuel return line is used for lubricating and cooling the injectors and the injector pump. It is also used for bleeding air from the filters. The return line pressure is low; therefore, it is often made from a synthetic rubber hose material.

The fuel supply lines are usually made of seamless steel tubing, coated with tin to prevent rust. Sometimes cadmium is used instead of tin. Fuel lines must be large enough to provide enough fuel flow for maximum power. They are supported under the vehicle by nylon insulators in brackets. Sections of reinforced synthetic rubber hoses allow for movement, and vibration of components. The reinforcement is needed because the fuel line is subject to variations in pressure, which usually run between 20 and 30 psi (138 to 207 kPa), to supply the injection pump with fuel.

High-pressure fuel injector lines connect the fuel injection pump to the injectors. Pressures in injector lines can reach up to 29,000 psi (200,000 kPa) on some engines. They are made of cold-drawn, annealed, seamless steel tubing. The bore of the pipe is kept to the smallest diameter possible, and all of the pipes are the same length. If pipes of different lengths were used, it would affect injection timing. It is important to understand that high-pressure lines should never be bent because doing so will cause them to flake internally, which can ruin the fuel injector.