sprinklernotes
Fire Pump Test Header Supply Pipe Sizing
You have asked the following question: “When sizing the piping to the test header, am I allowed to reduce down to a 4 in. pipe to go through the wall if Table 4.27 requires an 8 in. pipe to supply the test header?” In response to your question, we have reviewed NFPA 20, 2016 edition as the applicable standard. Our informal interpretation is hose valve header supply pipes are allowed to be sized by hydraulic calculations based on a total flow of 150 percent of rated pump capacity. The requirement for sizing test header (hose valve headers) supply pipes are located in Section 4.21.3.1.3, which states: Where outlets are being utilized as a means to test the fire pump in accordance with 4.21.1.1, one of the following methods shall be used: (1) Hose valves mounted on a hose valve header with supply pipe sized in accordance with 4.21.3.4 and Section 4.27 Section 4.21.3.4 allow one of two methods to be used when determining the pipe size. The most applicable method in this situation is the second option provided, which is: This pipe is permitted to be sized by hydraulic calculations based on a total flow of 150 percent of rated pump capacity, including the following: (a) This calculation shall include friction loss for the total length of pipe plus equivalent lengths of fittings, control valve, and hose valves, plus elevation loss, from the pump discharge flange to the hose valve outlets. (b) The installation shall be proven by a test flowing the maximum water available. This allows the piping to be sized per hydraulic calculations. However, Section 4.21.3.1.3 requires test headers supply pipes to meet both Sections 4.21.3.4 and 4.27. Section 4.27 states: The sizes indicated in Table 4.27(a) and Table 4.27(b) shall be used as a minimum. This requires the sizes listed in Table 4.27 to used as a minimum, which appears to be in conflict with Section 4.21.3.4. However, Note 4 of Table 4.27 test headers to be size per Section 4.21.3.4. Note 4 of Table 4.27 states: The hose header supply is permitted to be sized in accordance with 4.21.3.4. Thus, as long as hydraulic calculations support reducing a portion of the test head supply pipe from 8 in. to 4 in. and proven by a flow test after installation, it is an acceptable installation.
