FIRE FLOW TESTING SERVICE
Flow tests are important for determining the effciency and adequacy of the distribution system for transmitting water, particularly during peak demand, and to determine the amount of water available from hydrants for fire fighting. To perform such tests it is necessary to induce a flow from one or more hydrants within the area of the testing, and gauge another non-flowing hydrant to determine static and residual pressure with the upstream or downstream hydrant flowing fully open at the 2-1/2" nozzle. To determine flows, or gallons per minute, from a hydrant, a hydrant pitot gauge must be used. This is an instrument with a tube which has a small hole in one end which is centered in the stream flowing from the 2-1/2" nozzle. The velocity of flow is transmitted as pressure to a pressure gauge attached to the tube. The National Board of Fire Underwriters (NBFU) generally prescribes that there should be a certain flow, such as at least 500 GPM at a test location with a residual pressure of no less than 20 psi. Some cities and town's Fire Chiefs require between 800 to 1000 GPM with a 20 psi residual. This can only be achieved if the normal static pressure within the system is at least 80 psi.