Foam Concentrate Proportioning

Line proportioners (or eductors) allow a simple, cost-effective method of proportioning foam concentrate and water at the proper ratio to produce foam. These constant flow devices will proportion concentrate at a specified flow and pressure. Fire systems that use such proportioners must take into account the typically 35% friction loss through these devices to achieve a workable operating pressure at foam discharging devices. System designers must also ensure the proportioner(s) is mounted at a maximum height between 2.4 to 3.0 metres above the minimum expected foam liquid surface.

Balanced pressure bladder tanks are made of an ASME pressure vessel containing an internal rubber bladder that holds the foam concentrate. Progard has available bladder tanks with prepiped ratio flow controllers. During operation, water is applied to the outer surface of the bladder. This subsequently displaces the foam concentrate, which then makes its way to the proportioning device or ratio controller at the exact point where the foam concentrate is injected. Bladder tanks are reliable, economical and usually trouble-free. As water is the primary operating medium, they are easy to operate and require little maintenance. Widely used in small aircraft hangers, warehouses and helidecks where easy to operate and economical systems are advantageous.

Balanced pressure in-line or pump proportioning systems are an alternative to bladder tanks. The balanced pressure pump proportioning skids are generally used in situations where flexibility of concentrate proportioning is not critical. These units have the foam concentrate proportioner on the same skid as the foam pump and use a diaphragm type balancing valve to achieve accurate proportioning. They do not require any manual adjustment and are generally limited to one or two ratio controllers per skid.

Alternatively, the in-line balanced pressure proportioners (otherwise known as ILBP) are designed for applications requiring large quantities of foam concentrate. These units offer greater flexibility and can accommodate an almost indefinite number of risers, each one having a different size proportioner and each offering a wide range of flows. These ILBP systems include an atmospheric foam concentrate storage tank and foam pump. The tanks are manufactured from stainless steel, mild steel or high density polyethylene, depending on the concentrate used. Foam concentrate is pumped to the ratio controller. A diaphragm balancing valve is used to control the flow of foam concentrate into the ratio controller metering orifice that balances the water and foam concentrate pressures. Foam pumps used for ILBP systems are typically positive displacement pumps. However on high foam concentrate flows, centrifugal pumps are used.

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