You have had success using Class A foam during fire training exercises to combat automobile interior and other ordinary combustible fires, and youâ€™ve now decided to implement nozzle-aspirated Class A foam. You already own a 95-gpm eductor that can be used during fire responses. The device has...
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You have had success using Class A foam during fire training exercises to combat automobile interior and other ordinary combustible fires, and youâ€™ve now decided to implement nozzle-aspirated Class A foam. You already own a 95-gpm eductor that can be used during fire responses. The device has been virtually unused since its purchase and is located in the driverâ€™s-side tool compartment of your first-out engine. While eductor technology is simple and requires only a few operational changes, increasing your knowledge of how these systems work, along with understanding system design features, capabilities and limitations will benefit you and your department in making more successful fire stops.
Eductors remain one of the easiest and least expensive ways to become involved in the application of nozzle-aspirated Class A foam. Based on simple design principles, eductors create an area of low pressure inside, which lets foam concentrate be forced into the eductor due to greater external pressure exerted by atmospheric air on the foam concentrate supply. Eductors have an inlet pressure rating, usually 200 psi, and a flow rating, such as 95 or 125 gpm, where the particular device is designed to operate. All eductors have a specific proportioning ratio range over which they can educt foam concentrate. (Foam proportioning ratio is defined as the percentage of foam concentrate that is metered into a plain water stream to produce foam solution). Older eductors will have metering valves with proportioning ratios of 1%, 3% and 6%. Newer eductors will also have a 0.5% setting specifically meant for use with Class A foam agents.
Older eductors can be used successfully with Class A foam. Even though newer eductors are more attractive, since they are equipped with a 0.5% proportioning ratio setting, an older eductor with a minimum proportioning ratio setting of 1% can still be used utilized for Class A foam needing to be proportioned at 0.5%. To do this, take a 10-gallon bucket and pour in five gallons of water. Take a five-gallon pail of Class A foam concentrate and slowly pour it into the water, mixing it gently with a small paddle. You can use the resultant foam concentrate/water mixture with the eductor set at a 1% ratio. The final proportioning ratio will be 0.5% since the foam concentrate was cut to half strength by adding an equal amount of water.
The two popular types of eductors found today are â€œinlineâ€ and â€œbypass.â€
Bypass eductors are typically plumbed into fire apparatus discharge piping inside the pump house and can be operated in either the â€œbypassâ€ or â€œfoam solutionâ€ position. When operating in the bypass position, water flows through the eductor with little restriction and foam concentrate is not siphoned into the water stream. This allows the use of higher plain water-flow rates than that possible when the eductor is set in the â€œfoamâ€ position. When placed into the â€œfoamâ€ position, water flow inside the bypass eductor is diverted into a narrow waterway (the eductorâ€™s â€œthroatâ€), which allows for foam concentrate pickup.
Inline eductors are externally mounted to a fire pump discharge and are typically kept as â€œlooseâ€ equipment on the apparatus. They are manually installed on an apparatus pump discharge outlet when the need arises during a fire response.
First among the issues encountered in proper operation of an inline eductor is hoseline diameter selection and hoseline length. All eductors should be purchased with information from the manufacturer regarding appropriate hoseline diameter and maximum hoseline length where the eductor can be used successfully. Due to design limitations inherent in all eductors, hoseline back pressure limits the total developed hoseline length and/or elevation of the nozzle. A hoseline creating too much back pressure will not let the eductor operate correctly and thus the eductor may not â€œpick upâ€ the foam concentrate. Typically, 150 feet of 1Â½-inch hose or 200 feet of 1Â¾-inch hose is considered acceptable for eductor performance. Consult with your specific eductor manufacturerâ€™s literature for hoseline size and maximum hoseline length limitations.