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A flexible inner tank, positioned inside a conventional steel or FRP outer tank.
The inside containment is provided by a flexible impervious bladder, built in the shape of the tank. The bladder is folded and inserted through a manway into the outer tank (steel or FRP). Compressed air is then introduced into the bladder, forcing it to unfold and fit against the walls of the rigid outer tank.
The outer surface of the bladder unit is crisscrossed by a network of tiny channels. A vacuum is drawn on the space, created by these channels, between the flexible inner tank and the outer tank. The force of the vacuum pulls the flexible inner tank snugly against the walls of the outer tank.
The inner bladder tank serves as the primary containment unit for the gasoline, diesel fuel, or other product being stored. If the bladder should leak, the stored product would be contained by the rigid outer tank. Moreover, a leak in either the inner bladder or the outer tank would cause a disruption of the vacuum, continuously maintained on the space between the inner and outer vessels. The disruption of this vacuum would signal the presence of a problem.
A different type of bladder tank is used in military operations.
These bladder tanks are large “pouches,” made of a rubberized material. Each is capable of containing several hundred to several thousand gallons of motor fuel. The bladder tanks are transported–usually by helicopter–to invasion sites, such as beachheads. There, they serve as refueling points for military tanks and other vehicles.