Are there any good practices or other viable options allowed by NFPA 20 (other than a Pressure Limiting Driver) to limit the fire pump discharge pressure to at churn to 175psi when there is a high static pressure on the water supply?
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14 Comments
Alex
7/25/2022 05:18:46 am
Can you install a PRV immediately down stream?
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Dan Wilder
7/25/2022 08:04:47 am
Talk to your pump rep to get the flattest impeller curve available or maybe (if the water supply is strong enough) increase the GPM of the pump to bring your actual demand point onto a lower part of the curve before it hits 100%. Placing a PRV immediately downstream of the pump is the only other option (verify a low flow bypass isn't required) however, make sure the jockey pump is set correctly.
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Darin
7/25/2022 08:12:26 am
How about an adjustable pressure regulator at the BF device prior to the pump intake
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Glenn Berger
7/25/2022 08:14:36 am
Prior to actually designing or installing any deviations to NFPA 20, you need to get the AHJs approval.
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Eric
7/25/2022 08:18:22 am
I'm working on a fire pump with this particular issue atm, so good timing on the question! Your two choices are either a PRV after the pump assembly and before the transition to the sprinkler system riser, or a relief valve piped to a safe discharge location.
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Greg
7/25/2022 08:19:17 am
If the answer is not being found within the pump driver, or pump / impeller set up, and the problem is more of a water-hammer issue, I would suggest reading the following blog on topic by Bermad, a manufacturer of pressure reducing valves and pressure regulating bladder tanks.
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David Kendrick
7/25/2022 08:26:40 am
Forgive me, I should look up the current standard.
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Casey Milhorn
7/25/2022 09:08:44 am
Don't forget if you are adding a PRV before a feed to standpipes, then you must install (2) PRVs (pressure reducing valves) in series with a bypass around them. (Per NFPA 14). When feeding more than 2 hose valves.
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Dave
7/25/2022 11:28:58 am
Be cognizant of restrictions on the use of PRV's on fire pump system piping in NFPA #20 "Maximum Pressure for Centrifugal Pumps" section (4.7.7 in the 2013 through 2019 editions). If you have the NFPA #20 Handbook, it goes into even greater detail.
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Franck
7/25/2022 01:09:17 pm
As indicated by Dave, PRV is mandatory per NFPA 20
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Greg
7/26/2022 04:03:31 pm
I'm wondering now if the question involves a supply from a elevated water tower, tank on a high-rise building, or an outside water cistern on a mountaintop ?
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Jack G
7/26/2022 05:13:05 pm
Its possible to recirculate the relief valve discharge back into the suction to control the excess pressure.
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RAYMOND DELLING
7/27/2022 05:45:06 am
To add to the Question.
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Casey Milhorn
7/27/2022 11:48:08 am
In my opinion, no, 1 to 2 psi or even 5 to 10 psi isn't a big deal. We all have systems we've installed right at 175 psi churn and the pump over performs, or the water supply gets better. Many pump suppliers will go ahead and quote a 250 psi flange on the discharge of the pump when approaching 175 psi total churn, with this expectation.
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