In previous editions of Firehouse® Magazine I began to unshroud some of the mystery that surrounds firefighting foams for many of us. In those articles we looked at nozzle selection and required flow rates for incidents involving Class B fuels (flammable and combustible liquids...
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A jet ratio controller (JRC) may be used to supply foam concentrate to a self-educting master stream nozzle (Figure 6). The JRC is a type of in-line eductor that allows the foam concentrate supply to be as far away as 3,000 feet (900 m) from the self-educting master stream foam nozzle (Figure 7). This allows firefighters, who are involved in operating fire pumps and maintaining the foam concentrate supply, to be a safe distance from the fire. The JRC also allows an elevation change of up to 50 feet (15 m).
The JRC is supplied by a hoseline from the same pump that is supplying other hoses to the nozzle. The flow of water to the JRC represents about 2.5% of the total flow in the system. As with a standard in-line eductor, as water flows through the JRC a Venturi is created that draws concentrate through the pickup tube and into the hoseline. The difference is that the JRC proportions the concentrate at a 66.5% solution. This rich solution is then pumped to a self-educting master stream foam nozzle where it is further proportioned with the water supplied by the fire pump down to a discharge proportion of 3%. To achieve a proper proportion, it is important that the JRC and nozzle match.
In this article we have acquainted you with some important foam terminology and the most basic type of foam proportioning equipment: in-line eductors. In our next installment we will examine the various types of apparatus-mounted proportioning systems that are available to the fire service.
Mike Wieder is a senior editor at IFSTA/Fire Protection Publications at Oklahoma State University. He holds several degrees in fire protection and adult education. He is a former member of the Pennsburg, PA, and Stillwater, OK, fire departments. Part 1 of this series was published in the April 1997 issue; Part 2 appeared in May 1997.