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When specifying tank systems for standby power installations, consider not only fuel capacity, but also regulatory requirements, end-user needs and physical limitations of the site
Considering the over-all complexity of a standby power installation, a day tank or sub-base tank appears fairly simple by comparison. It is essentially a welded metal structure with fittings to let fuel in and out, and typically includes some accessories such as gauges, vents, pumps and motors.
In fact, specifying a day tank or subbase tank can be more complex than it appears. Some seemingly minor missteps in the specifying process can result in big, expensive problems later on.
Specifying and designing a genset fuel supply system means more than determining gallon capacity. It requires familiarity with the regulatory environment and a careful balancing of user needs and physical limitations.
Day and sub-base tanks defined
At its most basic, a day tank pumps diesel fuel from an above- or belowground main tank, stores it briefly and then delivers it to the genset. Even if there is a disruption in the main fuel supply, the genset continues to use the fuel in the day tank, thereby providing time to correct the problem.
Day tanks typically range in size from about 10 to 1000 gallons. The term "day tank" was coined in past years when the tank was expected to hold enough fuel to run the genset for 24 hours. As power requirements have increased, it is not always practical to size the day tank for a 24-hour fuel supply.
Day tanks can include certain accessories, such as alarm switches and other components to provide a warning in the event of a problem and to reduce the possibility of a fuel spill. At a minimum, day tanks generally include switches to detect low fuel level, high fuel level and fuel in the basin. These switches may be located on a control panel on the day tank or at a remote alarm panel.
A sub-base tank is a rectangular steel tank on which the genset is mounted. Thus, the genset draws fuel from the tank located directly beneath it. Sub-base tanks have grown in popularity in recent years because, in many cases, they eliminate the need for a large above- or belowground...