Calculation Needed for Fire Pump Test Off Roof?

11/1/2019

When testing a fire pump from the roof is there a calculation that is necessary to ensure that the flow test is accurate (given pipe sizes, elevation increase, etc)?

NFPA 25, 2014 handbook states that flowing from the roof in the explanatory material is somewhat acceptable (NFPA 25, 2014: 8.3.3.1.3). However, NFPA 20, 2013 A.4.20.3.4(2) has a sample hydraulic calculation sheet for sizing the test header when not using the table which appears to take into account items like friction loss, elevation, etc.

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3 Comments

Cliff

11/1/2019 01:38:47 pm

As long as your pressure readings are taken at the fire pump, no adjustment is needed. The only reading you should be taking at the roof is a flow reading and that is what it is. If the Fire Marshal is looking to confirm the pressure at the roof, that reading may also be taken but that is not part of a fire pump test.

Jeff

11/1/2019 03:10:52 pm

Cliff,

Isn't there an issue with the length of the pipe from the discharge of the pump? NFPA 20 requires you to make the test header pipe the next size larger when the distance is greater than 15' (NFPA 20, 2013: 4.20.3.4(1)). In the case of testing the pump from the roof, the distance could be > 100' of total pipe not to mention the additional fittings.

Also, with testing from the roof, the roof manifold may be on a smaller size standpipe than even the minimum test header pipe size. For example if there is only a 4" roof manifold with 2 hose valve outlets, the roof manifold pipe size would be below NFPA 20's current day minimum requirements If we had a 750GPM pump, the header size would need to be 6" per NFPA 4.26, then because it is > 15' away it would need to be 8".

Cliff

11/4/2019 08:13:39 am

It is my understanding, and someone please correct me if I'm wrong, that the pipe size increase is intended to make sure that the test header piping can support testing the fire pump to 150% of the pump's rating. The increase is not necessary if you can prove hydraulically that the pipe size will work. You may find that you can't reach 150% of the pump's rating while flowing at the roof. You can check this by running a standard hydraulic calculation; flowing 1125 gpm through the standpipe system back to the fire pump.

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