For a horizontal split case fire pump, 10 pipe diameters of straight pipe is to be provided for the suction inlet.
My design includes a gate valve and strainer within the 10 pipe diameters.
Is the strainer allowable in this range?
I'm unable to find in NFPA 20 any input on this. Thanks in advance.
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2/24/2023 07:04:28 am
While not specifically called out, the intent is to provide laminar flow to the pump via the 10 diameters of straight pipe with the correct orientation of elbows/tees when installed to the centerline of the pump.
2/24/2023 08:13:27 am
The 10 pipe diameters needs to be maximized as much as possible without the presence of any device which can cause a non-laminar flow condition.
2/24/2023 08:31:14 am
I agree with Dan and Glenn, and just to be clear, there is NOT an issue with a vertical change of direction for elbows/tees within 10 pipe diameters of the suction. This only applies to elbows/tees that create a change of direction in a horizontal fashion.
10 pipe diameters straight suction pipe rule that is specifically for horizontal split case fire pumps is not because of turbulent flow concern, it is because of pressure difference on both sides of the impeller that may ruin the pump.
2/24/2023 09:00:01 am
I think turbulence is too broad of a term here. It would be more in line with air entrainment or cavitation. You could probably argue that the strainer "could" cause one or both of these conditions.
2/24/2023 09:32:37 am
I agree with others this morning, I would not instal the strainer within the 10’.
2/24/2023 09:40:48 am
My advice would be to tread carefully, as it could be a high-risk decision $$$$.
2/24/2023 09:56:32 am
If the strainer does its job and traps something within 10' of the suction side of the pump wouldn't that be as bad as a valve clapper? .. create pressure differential on both sides of the impeller?
2/24/2023 11:12:07 am
My personal opinion is that it would be ok, but I would try to to put it furthest away from the pump suction as possible. I definitely would check to see if it’s ok with the AHJ.
2/25/2023 02:00:24 am
I would be very cautious with anything located on the suction side susceptible to create unbalanced flow, turbulences, caviation, blockage...
2/26/2023 03:08:35 am
I'd say the intent from NFPA 20 is not to have strainers on suction pipes for centrifugal pumps whether in a 10x NB location or otherwise. If you do fit them, I think you would have to make assumptions in your calculations for the strainer to be clogged.
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