You don’t draw a main down to zero at a fire. While I’ve pumped enough water so that intake gauge on my pump panel is just a couple psig above zero, the pressure at the main is higher. There is friction loss in the barrel of the hydrant, at that hard right angle it take leaving the and in the soft suction (supply) line (hose), and maybe even a theoretical loss in the pump inlet.
That said, when you are down this low, and you are using a short piece of hose without kinks, pressure at the main is less than 20psi. So where does 20 psi come from? I am not going to quote chapter and verse, but if you move over to the AWWA side of the world, including whoever enforces clean drinking water in your state or province, 20psi is nearly holy writ. One goal is to keep any leaks flowing clean water into the soil and keeping dirty water out of the pipes. A sanitary sewer joint might be only 10 ft away. It is guaranteed that a few leak. So once this is established in their world everyone uses it. Gaskets in slip on joints have to be designed and tested so that at the low end they seal at 20 psi, and so on. You will see this number appear in standards talking about connections supplying fire pumps. Until there is smoke the water main system belongs to the water purveyor. Even when there’s smoke they are just letting us use it. Best Bruce Verhei > On Oct 24, 2017, at 14:41, Bruce Verhei <bver...@comcast.net> wrote: > > I’d expect that a fire flow calculation has already been done by the fire > plan reviewer. The architect and CE should already have a copy of the > calculations. These are often done quite early in the project so there may be > more than one set, e.g. one set of calculations for a Type V-N and another > for a Type V-One Hour building. Confirm which type of construction the > architect has chosen. > > Sometimes construction type cycles around during early process. You get a > different answer on Monday than on Thursday. You need to be assured > construction type is finalized. I would not assume site engineer has current > or correct information. This is the architects balliwic. > > Best > > Bruce Verhei > >> On Oct 24, 2017, at 12:53, Parsley Consulting <parsleyconsult...@cox.net> >> wrote: >> >> Bobby, >> >> Not sure which area you're working in, however there is an appendix B to the >> IFC or it's variants which shows how much fire flow is required for a >> building based on it's square footage and construction type, with the >> required pressure being 20 psi at the hydrant, at least in the IFC and CFC >> I've worked with. >> >> The number of hydrants required to deliver that flow is established in the >> next appendix, C. >> >> As I'm the soon-to- be ex-chair of the NFPA 24 committee please see the >> disclaimer below. >> Ken Wagoner, SET >> Parsley Consulting >> 350 West 9th Avenue, Suite 206 >> Escondido, California 92025 >> Phone 760-745-6181 >> Visit the website >> >> IMPORTANT NOTICE: This correspondence is not a Formal Interpretation issued >> pursuant to NFPA Regulations. Any opinion expressed is the personal opinion >> of the author and does not necessarily represent the official position of >> the NFPA or its Technical Committees. In addition, this correspondence is >> neither intended, nor should it be relied upon, to provide professional >> consultation or services >> >> It should be noted that the above is my opinion as a member of the NFPA >> Installation of Private Fire Service Mains and their Appurtenances Committee >> in accordance with the NFPA Regulations Governing Committee Projects and >> should therefore not be considered, nor relied upon, as the official >> position of the NFPA or its Committees >> >> >>> On 10/24/2017 12:24 PM, Welch, Bobby wrote: >>> I am working on a underground project were the new private fire main is >>> feeding the building sprinkler system and two hydrants. I am told that the >>> underground has to be calculated. I understand how I calculate the building >>> to prove that the sprinkler system will work but how do I prove that the >>> hydrants work as well? >>> >>> >>> _______________________________________________ >>> Sprinklerforum mailing list >>> Sprinklerforum@lists.firesprinkler.org >>> http://lists.firesprinkler.org/listinfo.cgi/sprinklerforum-firesprinkler.org >> >> _______________________________________________ >> Sprinklerforum mailing list >> Sprinklerforum@lists.firesprinkler.org >> http://lists.firesprinkler.org/listinfo.cgi/sprinklerforum-firesprinkler.org
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