NFPA20 - Commercial Fire Pumps
NFPA-20 is the National Fire Protection Association's code section governing the construction and installation of stationary fire pump systems. Sections of this code cover everything from requirements for system component markings to temperature or altitude specific rating changes for diesel engines. For the novice, navigating these demanding regulations can be a daunting proposition and can seem needlessly complicated. The intense attention to detail in NFPA-20 is for good reason though, it ensures that systems are built correctly and will work as intended when they are needed. Every time.
Starting from a design condition, 2500GPM @ 80PSI for example, the first task in designing an NFPA-20 compliant system is to find a pump listed for 2500GPM @ 80PSI. Such a pump will have its suction and discharge connections sized to maintain water velocities at realistic speeds, its pressure produced at zero water flow (churn pressure) to correspond to performance criteria at 100% and 150% rated flow, provisions (depending on how its being driven) for temperature control, pressure regulation, air release, drainage, etc. A pump rated for 2500GPM will be usable at a wide range of pressures determined by the horsepower of the driver. So for the next step, a driver is selected.
Electric motors and diesel engines are the most common choices for fire pump drivers though NFPA-20 provides guidelines for the use of steam engine drives as well. From a horsepower perspective there is no difference between electric motors and diesels, either will work as long as they make enough power to make the pump do its job. Selection of a driver will be dependent upon where its being installed; the resourses available and possibly other equipment already on site. High horsepower electric motors run almost invariably on 460 volt or higher, 3-phase power. Using higher voltage lessens the amp draw required to develop a certain horsepower. In order to drive our example 2500GPM pump and create 80PSI the motor will need to be in the 200hp range. A 200hp motor supplied with 460 volt power will draw 250 amps running normally - with the potential to draw over 1500 amps if something goes haywire. Not every location will have enough power available or it may be prohibitively expensive. The alternative is diesel drive.
While electric motors are generally more compact than diesels, less of an environmental headache, and require fewer acoutrements, they are entirely dependent on infrastructure. A diesel drive will work anywhere as long as it has fuel. NFPA-20 contains even more regulations for diesel drives than electric as provisions must be made to handle the fuel system, cooling, exhaust, vibration, etc. To satisfy a design condition of 2500GPM @ 80PSI the diesel will also have to be in the 200hp range. Once the horsepower is known, a fuel tank can be selected. One gallon of fuel capacity is required per horsepower plus an additional volume to provide room for thermal expansion. Fittings on the tank are specified for venting of fumes, containment of leaks, determining fuel level without crawling inside… Cooling methods for the diesel engine may require different set-ups for cooling water supply, return, or drain piping. Using a diesel may require installing a pressure relief valve on the discharge side of the pump in case the engine revs out of control or, irreguardless of driver type, if a combination of suction pressure and pump pressure rise above a certain threshold. When roughing out an NFPA-20 compliant system the designer must know how each selected component will affect the selection of another or if the installation site can support the chosen equipment. As stated above this can be a daunting, yet necessary, proposition.
We at TALCO Fire Systems however, consider this our bread and butter. When you purchase one of our turn-key NFPA-20 fire pump packages we take full responsibility for all design and integration issues. Your installation of the complete fire pump system is reduced to connecting the main supply and discharge pipes and supplying the system with electrical power. Our custom TALCO NFPA-20 systems are designed and built from the ground up to fit your specific design conditions and site layout. These CAD designed packages are frame mounted, fully piped, fitted, and wired. All piping sections, as well as the frame members, are powder-coated to extend service life. With your choice of either electric or diesel driven systems in capacities as high as 5000GPM TALCO has you covered.