I have a fire pump rated at 100 psi at 1000 GPM. The curve for the pump is starts at 125 psi and goes to 0 GPM. I know 140% is the 125 PSI. On my hydraulic calculations should I use the 140% pump curve or should I use the 100% Pump curve? Where in NFPA 13/20 can I find this guidance?
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13 Comments
Phil Watkins
9/27/2019 10:29:59 am
I think you will find that you will have one pump curve from the manufacturer which should be produced to meet your system demand.
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ioan rincu
9/30/2019 02:13:16 pm
I have never seen a fully hydraulically calculated system.
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Cameron
9/27/2019 10:44:05 am
Typically you can develop your curve using three points. Churn, 100% and 150%. It sounds like you may have indicated that you have 125 psi at 0 gpm (churn), 100 psi at 1000 gpm (100%), then you would need to reference the manufactures curve to see what you have at 1500 gpm (150%). That should give you a curve to reference in your design. If you are only being allowed to use up to 140%, then see what your pressure is at 1400 gpm and don't let your demand exceed that point.
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Greg Stoner
9/27/2019 10:53:41 am
I believe this is accurate: A fire pump shall develop at least 65% of its rated head at 150% of rated capacity and shall not exceed 140% of it's rated head at zero capacity..
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Anupam Majumdar
9/27/2019 11:01:24 am
The hydraulic calculation should with rated capacity & head. No other consideration like 150% or 65& etc should not considered. after calculation if it founds that same is not fulfilling at 100%, then designer should re-calculated with revised pipe sizes.
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Colin
9/27/2019 01:51:11 pm
Concur with Cameron. It sounds like at 0gpm (churn) you have 125psi, which is typical for a pump rated at 100 psi/1000gpm. The 140% pressure at 0gpm is the max allowed by NFPA 20, but most pumps are actually in the 120%-130% of rated pressure at churn, and your pump falls right in the middle at 125% of rated pressure at churn.
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9/27/2019 02:43:15 pm
It is important to know that the pump running at 150% flow (in this case it would be 1500 GPM), the engine delivers maximum power, therefore higher consumption, heat, vibrations and noise.
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DT
9/27/2019 06:49:56 pm
I think the question may need to be changed.
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Bobby
9/27/2019 07:03:15 pm
Can you clarify your circumstances; are you designing a system and in the process of specifying the required pump performance or has the pump already been identified and you know its performance ?
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Tim
9/27/2019 11:04:20 pm
I have identified my pump and I know it’s performance just wasn’t sure where I could design from. Thank you all for the responses it helped me feel more confident in the way I m using it. I would like to know where I can find that info in N.F.P.A. 13 or 20?
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Mike L
9/28/2019 05:33:54 pm
Your hydraulic calcs should be based on the duty point of the pump (in your case, 100 psi at 1000 gpm). The 140% pressure at 0 Flow and 65% pressure at 150% flow are pump design limitations set with NFPA-20 as theoretical limits.
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Ali Khan
3/1/2021 04:32:47 am
You are right
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