Fire pump bypass

[skdesigner]

NFPA 20-2007 5.14.4.1 Where the suction supply is of sufficient pressure to be of material value without the pump, the pump shall be installed with a bypass.

Has anyone qualified what "material value" is? Best answer I have received is that if the city supply can provide enough pressure and flow to make 4 sprinklers work, then it is of material value, as most fire are extinguished with one or two heads.

Just finishing a warehouse with 16.8k ESFR pendants and a 1,500 gpm diesel pump. City pressure sits around 45-50 psi static and drops to 30 psi while flowing about 2,500 gpm. Based on height, the sprinklers need minimum 52 psi to operate.

It appears this is a case where the suction supply is not of material value. The 8" pipe and fittings that went in to the bypass, however, are quite valuable.

Anyone install big pumps with no bypass?

 

[TravisMack]

Do you have any office spaces in your system? How about any bathrooms or anything protected with standard spray sprinklers? Since there is no definition for "of material value," I would not want to be the one that left out the bypass and something bad happened during a fire event.

I have only left the bypass out when the system is fed from a tank.

Travis Mack
MFP Design, LLC

http://www.mfpdesign.com

 

[MGXFP]

I have only left it out when it is a tank + pump at a lower elevation relative to the floor of the building protected i.e. the water level wouldn't reach the sprinklers if not assisted by the pump. If it can deliver water to the sprinklers I think that is of material value. This is only my opinion.

 

[skdesigner]

Interesting. For what it's worth, my pump installations have always been done with bypasses, just wondering if anybody did it differently.

Thanks for the responses, both make complete sense.

Steve

 

[Oremus]

That's been my rule of thumb as well - if there is enough pressure that any amount of water will come out of the pipes then it's of material value given the alternative; no bypass means no water at all if the pump locks up.

 

[LCREP]

Some water is better then No water

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Fire Sprinklers Save Firefighters’ Lives Too!

 

[cdafd]

Was the bypass required in past editions and the wording got changed??

Thought it was there if the pump went bad and also if you had to pull the pump for maintence

 

[LCREP]

From NFPA 20, 2010 Fire Pump Handbook

In most cases, a pump that is connected to a public or private water supply should include a bypass. Only in rare cases, where the pressure available is so low that the water supply is of no value without the pump, should a fi re pump be installed without a bypass. When a pump
is supplied by a suction tank, a bypass is not needed (see Figure A.6.3.1(b) because a suction tank will not provide suffi cient pressure to be of value without the fi re pump operating. The valves on the bypass are required to be normally open so that the attached water supply is available automatically. In this case, “normally open” refers to the valve being in the open position at all times. The bypass valves should be closed only for system maintenance. In some cases, the function of the pump bypass is mistakenly thought to be used only when the fire pump is out of service. This function is not the intent of the standard, because the water from the bypass must be available automatically if the pump fails to start.

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Fire Sprinklers Save Firefighters’ Lives Too!

 

[ContractorDave]

skdesigner

PM me at my FPSSDave@live.com when you have a minute.

Thx
Dave

Regards
D

A thing moderately good is not so good as it ought to be
Thomas Paine

http://www.ykfireprevention.ca