Fact File 59 Extinguishing systems

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Hugh Wells
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1 Fact File 59 Extinguishing systems Foam Inductors: Guidelines on their selection, use and maintenance

2 Foam Inductors: Guidelines on their selection, use and maintenance INTRODUCTION... 3 HOW INDUCTORS WORK... 4 HOW INDUCTORS ARE USED... 5 INDUCTOR TESTING AND MAINTENANCE of 6

3 INTRODUCTION An inductor may be used to proportion fire fighting foam concentrate into a water pipeline at a specific flow and pressure. This means that an inductor must be matched with the nozzle(s) it supplies. It offers a simple and inexpensive means of proportioning where the water supply pressure is reasonably high - 5bar or above. This device may also be referred to as an eductor or line proportioner. Each inductor is designed and intended for use at a specific inlet pressure and water flow. An increase in pressure (and flow) will reduce the foam proportioning rate and a reduction in pressure (and flow) may result in loss of foam induction. Inductors may be portable for use in fire hose lines, or piped into fixed fire protection systems. Portable inductors are intended for use with one or two lengths of downstream fire hose to limit pressure losses between the inductor and nozzle. 3 of 6

4 HOW INDUCTORS WORK Inductors comprise an inlet nozzle with a chamber downstream, from which extends an expanding taper section leading to the inductor outlet. Connected to the chamber is the foam concentrate inlet connection, which incorporates a metering orifice. Water pressure applied to the inlet is converted into water at high velocity across the foam inlet, thereby creating a suction effect which draws foam concentrate into the chamber (Venturi effect) to mix with the water to produce foam solution. The rate at which foam concentrate is drawn in is controlled by the foam inlet orifice which is sized to suit the required proportioning rate (ie 1, 3 or 6%) and the viscosity of the foam concentrate to be used. When the foam solution enters the expanding taper section its velocity decreases and some pressure is regained. The pressure at the inductor outlet is approximately 65% of the pressure at the water inlet. Figure 1 shows a typical foam inductor. 4 of 6

5 HOW INDUCTORS ARE USED A portable inductor is provided with flexible suction hose complete with a foam inlet check valve. This enables the suction hose to be inserted into a drum of foam concentrate. In a fixed system, the foam inlet is usually piped to a dedicated foam concentrate atmospheric storage tank. In a piped foam suction line should be incorporated an isolating valve and check valve. In both applications, the check valve is to prevent water draining into the foam concentrate when the system is being shut down and the inductor suction is lost. For an inductor to perform correctly, there should be no change in the direction of water/foam solution flow within 600mm of the inlet and outlet of the inductor. Inductors should ideally be positioned below the level of the foam concentrate, but in no instance more than 2m above the minimum foam concentrate level. Portable inductors are not normally supplied with a long enough pick-up tube that would allow them to be used in this way. Nor should the nozzle(s) be more than 6m elevation above the inductor to prevent back pressure affecting the performance of the inductor. 5 of 6

6 INDUCTOR TESTING AND MAINTENANCE As with all fire fighting foam systems, the proportioning accuracy of each inductor should be verified annually by testing. Maintenance and post use of inductors comprises: Flush the inductor with fresh clean water Inspect for damage/corrosion Check hose/pipe connections are secure Replenish foam concentrate supplies Inductors generally cannot be repaired on site, so the manufacturer should be consulted with details of any problems. DISCLAIMER The information set out in this document is believed to be correct in the light of information currently available but it is not guaranteed and neither the Fire Industry Association nor its officers can accept any responsibility in respect of the contents or any events arising from use of the information contained within this document. Tudor House, Kingsway Business Park, Oldfield Road, Hampton, Middlesex TW12 2HD Tel: +44 (0) of 6

To establish a standardized procedure for Class B foam application by engine companies.

To establish a standardized procedure for Class B foam application by engine companies. PURPOSE: DATE Reviewed June 27, 2013 SARASOTA COUNTY GOVERNMENT EMERGENCY SERVICES DIRECTIVE VOLUME #2 FIRE OPERATIONS NUMBER #223 CATEGORY RECOMMENDED OPERATING GUIDELINE SUBJECT Class B FOAM EQUIPMENT