NFPA 20 Fire Pump Pipe Sizing

Pressure Relief Valve: (1) The PRV is to be sized per Table 4.28. (2) If the pipe employs more than one elbow, the next larger pipe size shall be used (4.20.6.1.1). (3) The PRV shall be permitted to be sized hydraulically to discharge sufficient water to prevent the pump discharge pressure, adjusted for elevation, from exceeding the pressure rating of the system components (4.20.2.1). (4) For more rules regarding routing, combining, and isolating PRV piping see 4.22.1/2.

Flowmeter Device: (1) The FMD is to be sized per Table 4.28. (2) The FMD is permitted to be sized in accordance with 4.22.2.3. (3) Where a metering device is installed in a loop arrangement for fire pump flow testing, an alternate means of measuring flow shall be provided. The alternate means of measuring flow shall be located downstream of and in series with the flow meter (4.22.2.10/10.1). (4) For more rules regarding routing, combining, and isolating Flowmeter Devices see 4.20.6/7/8/9.

Test Header: (1) The TH is to be sized per Table 4.28. (2) The TH supply is permitted to be sized in accordance with 4.22.3.4. (3) A listed indicating butterfly or gate valve shall be located in the pipeline to the hose valve header (4.22.3.3.1). (4) A drain valve or automatic ball drip shall be located in the pipeline at a low point between the valve and the header (4.22.3.3.2). (5) Per 4.22.3.4 (5a) Where the pipe between the hose valve header and the connection to the pump discharge pipe is over 15 ft (4.5 m) in length, the next larger pipe size than that required by Section 4.28 shall be used. (5b) Where the pipe between the hose valve header and the connection to the pump discharge pipe contains more than four fittings that create a change in direction, the next larger pipe size than that required by Section 4.28 shall be used. (5c) This pipe shall be permitted to be sized by hydraulic calculations that match the actual test configuration and that include the required pitot pressure and friction loss for the total length of pipe and fire hose plus equivalent lengths of fittings, control valve, and hose valves, plus elevation loss, from the pump discharge flange to the discharge outlets. (6) For more rules regarding routing, combining, and isolating the Test Header see 4.22.1/2/3.

Pump Flanges: The actual diameter of pump flanges are permitted to be different from the pipe diameter.

Pump Suction Pipe Size: Suction pipe size applies only to that portion of suction pipe specified in 4.16.3.3. Suction pipe sizes in Table 4.28(a) are based on a maximum velocity at 150 percent rated capacity to 15 ft/sec in most cases.