Proportional-tank foam systems

There are several different types of foam systems which can either use a traditional sprinkler pipework system employing a proportional-tank mechanical foam insfallation, shown in Figure 4.2.12, in the supply line to... 

These systems are typically provided for the protection of atmospheric or low pressure storage tanks. They consist of one or more foam chambers installed on the shell of a tank just below the roof joint. A foam solution pipe is extended from the proportioning source, which is located in a safe location, to a foam aspirating mechanism just upstream of the foam chamber or pourer. A deflector is usually positioned on the inside tank wall at the foam chamber. It is used to deflect the foam against the tank wall and onto the surface of the tank or the tank and shell seal area. 

Water is allowed to enter the foam tank from the main stream with as little friction loss as possible, while pressure in the main stream is dropped about 10% through use of an orifice. Liquid in the tank is metered into the low pressure area by a second orifice. The pressure proportioning system offers the advantages of low pressure drop, automatic proportioning over a range of flows and pressures, freedom from external power and the absence of moving parts. Its disadvantages are that the concentrate cannot be resupplied while the system is in operation, the bladders tend to leak and there is an economic maximum limit on size. 

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See also in sourсe #XX -- [ ]

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