NFPA13D - Residential Fire Pumps
Residential fire pumps generally fall under the National Fire Protection Association's 13D codes. NFPA-13D covers the construction and installation of fire sprinkler systems for one & two-family dwellings and mobile homes. 13D says very little about standards for the fire pump itself, it simply states that if the city water supply is insufficient to meet sprinkler demand then a fire pump and water storage tank are required.
Sprinkler demand in a residential system is normally calculated by the water flow required to run two sprinkler heads simultaneously for 10 minutes. A common flow for sprinkler heads is 15 gallons per minute. This means that a normal home with a normal system would require a 30GPM supply in order to meet code. Since standard utility company meters can't keep up a homeowner/builder has the choice of having a larger meter installed (these cost a lot to begin with and come with a monthly charge whether their higher capacity is used or not) or buying a water storage tank to meet the 10 minute supply demand. Water tanks are cheap and cost nothing once installed.
Water flow is only one of the factors in sprinkler demand though. The other is pressure. In order for the sprinkler head to cover enough area to be effective it must have the water delivered with enough force(PSI). Many homes will have enough pressure. However, pressure without flow won't put out a fire. This leads back to the choice of either having a larger meter installed, along with its monthly charge, or buying a 13D system and tank. 13D systems are often much cheaper than the larger meters and cost nothing once installed.
Since NFPA-13D says very little about how a fire pump should be constructed, many are cobbled together with little attention paid to function or real performance. A contractor can get away with just installing a pump & motor, a pressure switch as a controller, a ball valve & check valve, and meet the minimum code requirements. While a system such as this will meet code it has little chance of doing its job in the case of a fire. When a pump controlled only by a pressure switch turns on it builds up pressure rapidly. Almost instantly it will reach the shut-off point determined by the pressure switch. The pump will then turn off and the pressure will fall just as rapidly. When the pressure reaches the turn-on point the switch will activate the pump and the system pressure will jump again. This process, called rapid-cycling, will repeat several times a second until the associated heat build-up trips the thermal over-load in the pump motor. In our tests rapid-cycling pump motors last nowhere near the 10 minute minimum-run-time required by NFPA-13D. Also, a sprinkler head supplied by a rapid-cycling pump throws water in pulses, never reaching its full coverage radius or flow. A pressure switch alone is not enough.
Several work-arounds can solve the problem of rapid-cycling. Small pressure tanks attached to the pump discharge can store a supply of water at system shut-off pressure and slow system pressure spikes. While the pressure tank approach is effective for a while, it relies on the longevity of a rubber bladder kept under pressure by a bicycle-tube valve on the tank. When (not if, when) the air leaks out the tank becomes useless. A better solution is a real set of electronic controls that will keep the motor running for a pre-set amount of time and also provide surge and over-current protection. Unless your plumbing contractor moonlights as an electrical engineer, a cobbled together pump system is unlikely to include a full suite of automatic controls.
That's where we come in. Our LSF Compact Residential Fire Pump systems are backed by years of expertise and are fully tested before they leave our facility. We also include important safety features not offered on any other system in our price range because lives depend on it. With 10 models capable of anywhere from 25 to 170 GPM flow, system pressures of up to 95 PSI, and all small enough to disappear into a corner, TALCO has your residential fire protection needs covered.