Fire Pump Cut-in Pressure

[canadeng]

Hello everyone, I hope I can get some input on this question. I am working working with an owner on the review of his fire pump system. The campus has approx. 5 building spread out over the property and has a pump house with a primary electric vertical turbine fire pump and a back-up vertical turbine diesel fire pump taking water from a domestic/fire water reservoir. Each pump is rated at at 1,000 gpm at 140 psi, with a churn pressure of 161 psi. There are 2 domestic pumps that are set-up to maintain 70 psi in the distribution piping (operating lead/lag). According to the pump commissioning forms the primary (electric) pump cut-in pressure is 45 psi, while the back-up (diesel) fire pump cut-in pressure is 40 psi. In this set-up with domestic booster pumps acting as the jockey pump do the cut-in pressures of the fire pumps seem reasonable?

Thank you.

 

[skdesigner]

Are the domestic booster pumps dedicated to the fire water system? Boosting a system from 45 psi to 161 psi in a matter of seconds could have some fairly serious ramifications. The system pressure should be maintained at or very near the fire pump discharge pressures.

 

[canadeng]

Hello skdesigner, the domestic pumps are not dedicated to fire pumps. There are a few plumbing fixtures in each building that they serve. It looks like a better design may have been to have 2 piping distributions, one for domestic at 70 psi and one dedicated for fire being maintained at around 120 psi by a dedicated jockey pump.

 

[MGXFP]

The pressures settings for the system should be set up as illustrated in NFPA 20 A.14.2.6(4). This doesn't seem to be set up correctly. The jockey pump should shut off near the fire pump churn pressure.

 

[skdesigner]

Do the fire pumps hit the domestic system with 161 psi when they turn on? Is this system actually installed, or just in the planning stages?

 

[LittleInch]

It looks like this is some weird sort of dual system whereby the "domestic" system is relatively small compared to the fire system.

I'm surprised this is allowed by your AHJ. does the fire department know about this?

40 psi to start seems low when the pumps can produce 140 to 160. will be an interesting jump when they kick in....

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