Fuel oil pumping
Gensets are equipped with gear-driven pumps in the engine ‘s common-rail which pressure fuel. The internal pump draws fuel from the tank behind it. The excess fuel which has not been pumped into the cylinders is returned to the tank. The pump has limited capacity in the fuel distribution system (piping, fittings, and filters) for priming and overcoming friction losses.
Two types of electric-driven fuel oil pumps are commonly used outside the genset: gear pumps and centrifugal submersible pumps — each with their own advantages and disadvantages.
Gear pumps: Such pumps may be internal or external gear types, mounted on a separate skid, and usually used for low-flow, high-pressure applications. The gear pumps are known as positive displacement pumps when pressure levels reach 40 psi. In addition, gear pumps with pressure capabilities exceeding 2000 psi are available. The gear pumps are machines with a constant flow rate, and their maximum discharge pressure depends on the power of the motor.
Submersible pumps: Submersible pumps used in high-flow, low-pressure applications need sufficient clearance above the fuel tank for accessibility and maintenance, even though much of the pump assembly is inside the tank. Priming or suction lift may not pose any problems.
During the design of the fuel system, the static lift and friction losses should be investigated in detail. The pumping system’s design flow rate should be two to four times the peak demand so that pumps run intermittently instead of constantly working to fill the auxiliary tanks.