YQA Generator Sub-Base Tank Fuel Refill

08.01 What is a generator base, sub-base, or belly tank?

Generator base, sub-base, or belly tank is a UL 142 fuel tank that is built into the frame of a generator support typically as part of a packaged unit that includes an enclosure. The tank acts as a substitute for a free-standing day tank.

Sub-base tanks can be classified as UL 142 double wall, L 142 single wall with containment dike, or UL 2085 fire rated.

08.02 What are the benefits of a base tank?

The benefits of a sub-base tank are: (a) saves floor space associated with a free-standing day tank, especially important for an outdoor fully enclosed generator package, (b) the engine draws directly form the tank minimizing piping costs and performance risks associated with suction piping.

For outdoor generators the sub-base tank can often be sized to allow for a 4, 8, or even 24 hour run time fuel storage requirement.

08.03 What are the problems with base tank

The problems with base tanks can include: (a) larger tanks raise the working level of the generator where steps and walkways can be required for routine inspection and maintenance, (b) the fuel tanks are subject to a higher level of vibration due to the construction within the generator frame, and (c) the large flat bottoms of the tanks with internal baffle construction, can promote biological growth within the tank.

08.04 How is the tank re-filled from a storage tank?

Base tanks are refilled in the same way as day tanks are re-filled with a couple of challenges: (a) limited room within the enclosure for mounting re-fill equipment, (b) shallow depth of tank may require special level sensors for refill control, and (c) shallow depth of tanks can make location of a properly sized overflow pipe difficult on the top sidewall of the tank.