150% rated capacity NFPA

Looking for advice on reaching NFPA requirements.

1970s fairbanks morse diesel driven fire pump

Rated 1000 gpm, 100 psi, 1750 rpm
Tank source at 10 psi, system kept at 100 psi

Churn test 115 psi net 1753 rpm
500 gpm 105 psi net 1722 rpm
1000 gpm 80 psi net 1712 rpm
Did not reach 1500 gpm at 65 psi net at 1700 rpm

My concern is that the building will never need 1000 gpm, nevermind 1500.

The rpms drop off below 1750 perhaps a diesel mechanic can tune it up to extend the usable life.

Also perhaps testing method issue? Used 2" nozzles, 1 for 500 gpm test, 2 for 1000 gpm etc, through little host monster apparatus. Could testing another way, less hoses etc that may change the results.

If we cannot remedy we will likely need full replacement. Any advice is welcome.

I would make sure you are running your hoses as straight as possible. Any kink or bend in the hose will mess with the pitot readings. Sometimes, there are going to be severe bends that are unavoidable, but you would be surprised how much a better reading you get when you take the kink out of the hose. When I’ve had outlets coming out of the test header at 10 to 2 o’clock, I’ll put a ladder under the hose to support it.

Another thing you can try is connect straight to the test header with play pipes - if the outlets are pointing straight out, of course. At least with that setup, you eliminate the hoses.

Just out of curiosity, has the pump ever reached 150%? If you think the pump is over-sized, maybe it’s time to recommend an engineering analysis on the system. At least that way if you end up quoting them a new pump, you’ll know what to properly size it for.

I’m not sure that it ever had in the past. At the time of install the 150% was not a required test. The pump in there now wouldn’t have a relatively flat h vs q curve that is like to see in there for a fire pump. The issue now is would it be worth sinking money into the engine to push out more juice vs getting a properly sized pump, with a lower 150% capacity, which could be met without needing more power from the older engine. I’m thinking it may be worth a diesel engine tune up and retest with minimal hose lengths, kinks, etc before replacing the pump. Thoughts?

In our jurisdiction, if 150% wasn’t required when installed, wouldn’t be required today. But wouldn’t hurt to try a tune up on the almost 50 year old girl! But then again, she’s almost 50 years old. I think they got their money’s worth out of it.