Todd, You’re right, sorry for not actually answering your question! IMO, splitting the distance over multiple straight lengths is fine. It’s all about actual travel distance from the illegal elbow to the suction flange.
Either way, with 17psi missing, I’m pretty confident that this is not the source of your problem. My best guesses would be time of day/year water pressure variations depending on what flow test information you are basing your calculations on, or a partially closed underground supply valve somewhere upstream. Is there a fire hydrant close to the pump-house on the suction side? I’d want to put a gauge somewhere further upstream so you can confirm the pressure loss you are getting along your underground suction pipe. Also definitely add a gauge on the inlet side of your backflow to make sure something isn’t wrong there. Hope this helps, Eric RIeve From: Fpdcdesign <[email protected]> Sent: Friday, July 14, 2023 2:07 PM To: Discussion list on issues relating to automatic fire sprinklers <[email protected]> Subject: [Sprinklerforum] Re: Elbows in pump suction Eric, My main question is if the 10 diameter requirement can be split into 2 section or does it have to be one continuous length? The problem is that the suction pressure on the pump test goes to 0 psi at 1500 gpm. Based on my calculations, it should be around 17 psi. I know what you are all thinking; we are below 20 psi and this pump is never going to flow 2250 gpm. Correct. This pump was oversized and installed in an undersized pump house as required by the Engineer. According to him, our job is to “make their design work and no substitutions are allowed”. Fortunately the system demand is about 1200 gpm so we may eventually be able to meet that demand. This is. 6 month cluster f*** that has been going on for 2-1/2 years. Todd G Williams, PE Fire Protection Design/Consulting Stonington, CT 860-535-2080<tel:860-535-2080> (ofc) 860-554-7054<tel:860-554-7054> (fax) 860-608-4559<tel:860-608-4559> (cell) On Jul 14, 2023 at 1:05 PM, <Eric Rieve<mailto:[email protected]>> wrote: Todd, Like Brett mentioned, going vertical to eat up pipe length is shown in the annex of NFPA 20, and I’ve seen/used that approach before. When you say there is a problem with the test, is this for a new fire pump installation? Are you not meeting your curve, and if so, are you off by a substantial amount? I was always under the impression that the un-balanced flow caused by the elbow being to close to the suction inlet was a “long-term, causes damage over time” sort of issue, so if your problem is on a new install, I’d want to double check that there isn’t some other cause. 38” of straight run obviously isn’t great or to code, but it’s not like the elbow is directly attached to the suction flange either. Backflow has OS&Y valves right? Hope this helps, Eric Rieve Rieve Fire Protection From: Fpdcdesign <[email protected]<mailto:[email protected]>> Sent: Friday, July 14, 2023 12:37 PM To: Sprinklerforum <[email protected]<mailto:[email protected]>> Subject: [Sprinklerforum] Elbows in pump suction I am working on a pump house that has a 1500 gpm pump with an 8” suction line (no reducer). There is an elbow in the suction line parallel to the pump shaft with a piece of pipe that is 38” from the suction flange and there is a problem with the test. We have to add another 42” from the parallel elbow to the flange. There is physically not enough room in the pump house to make it in a single straight run. My proposal is to turn the offending elbow looking up (so no linger parallel), add a 42” vertical piece to an elbow and pipe that back to the discharge from the backflow preventer. Can the 80” be split into 2 pieces? NFPA 20 says nothing about that but I was wondering how it works in real life. FYI, the backflow discharge is already over the 80” threshold. Todd G Williams, PE Fire Protection Design/Consulting Stonington, CT 860-535-2080<tel:860-535-2080> (ofc) 860-554-7054<tel:860-554-7054> (fax) 860-608-4559<tel:860-608-4559> (cell) _________________________________________________________ SprinklerForum mailing list: https://lists.firesprinkler.org/list/sprinklerforum.lists.firesprinkler.org To unsubscribe send an email to [email protected]<mailto:[email protected]>
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