FIRE PUMP TESTING USING A FLOW METER
Flow meters are used to measure fluid or gas flows in piping systems as well as to balance such systems. Flow meters have been an accepted method of testing fire pumps since the 1974 edition of NFPA 20, Installation of Centrifugal Fire Pumps. Flow meters also have been tested and approved by Factory Mutual since 1974.
The reason for choosing a flow meter is that it permits the convenience of testing net fire pump performance frequently without the cost of assembling a large group of personnel plus providing fire hoses and nozzles for each test. The test can be conducted any time of the year, and testing with a flow meter limits the amount of water being wasted. If one were to consider the traditional method of testing a 1,500gpm fire pump and flowing various combinations of hose streams in order to get the various points on a pump curve, such as flows related to suction and discharge pressures (net pressure), and each point on the curve is measured over a 10-minute period, more than 50,000 gallons of water would be wasted.
With a flow meter, those same points can be noted with no actual loss of water. If the fire pump draw s suction from the city water mains, at least one point on the curve should be duplicated by actually discharging water. With the 1,500-gpm pump, if three hoselines discharge 500 gpm for a minimum of five minutes, the loss would be only 7,500 gallons.
Another big concern with a full discharge pump test is the possibility of flooding the site or adjacent properties. This can result in flooded basements and streets, damaged landscaping, and other hazards.
Flow meters currently manufactured come in several different configurations. The flow sensor, which is inserted in the meter piping, could be a differential pressure tube, an orifice plate with special flanges, or a venturi. All of these flow’ sensors note a differential between upstream and downstream sides of the device. The meter most commonly used is calibrated to read flows directly in gpm. Older meters might have been calibrated in inches of water. Generally, a table was provided with those meters to convert the inches of water to gallons per minute. This device could be a bellows-type dial or a mercury manometer.
