John's analysis is pretty much what I came up with, except we are using 8" pipe to a hydrant outside the school. This is a new school being constructed behind an existing one. I don't think a hydrant on the road would be used as most trucks would go in the driveway to the new location. Sounds like this would be OK.
At 09:17 AM 8/24/2011, you wrote: >Todd, >I would first confirm the flow test data, as 46 PITOT pressure will give you >1138 GPM. The two GPM numbers are too close for comfort and may suggest a >single fire hydrant flow test was used to arrive at this data. Assuming the >flow test data is accurate look at the following: >Combined elevation and flow losses at 275 GPM are 30 PSI. >The 20 PSI minimum will be at the point of connection, not at the elevation >of the fire pump. >At zero gallons flowing your static at the street is 54, at pump suction >will be (54-28) 26 PSI. >At 275 GPM your residual at street will be 53, while at pump suction it will >be (53-30) 23 PSI >At 500 GPM your residual at street will be 52, while at pump suction it will >be (52-28-6) 18 PSI. The 6 being loss in 6" DIP at 500 GPM. >At 750 GPM (for the one time you test the pump at 150%) the residual at >street will be 50 PSI, while the residual at pump suction will be (50-28-13) >9 PSI. The 13 being loss in 6" DIP at 750 GPM. >In no case will the residual be less than 50 at the city connection. Baring >any objection from the EOR, or an agent from the water purveyor who cannot >or will not read the calcs and flow curves, you should be OK. Remember you >will always have a positive pressure at suction, and the worse condition is >only at the onetime 150% pump test. >John O'Connor >National Fire Sprinklers, Inc. > >-----Original Message----- >From: [email protected] >[mailto:[email protected]] On Behalf Of Todd Williams >Sent: Wednesday, August 24, 2011 7:47 AM >To: [email protected] >Subject: RE: Minimum pressures in water supply > >The 30 psi does include elevation and friction. My guess is that the inlet >pressure of the pump would be around 16-18 psi. No, the pump house is part >of the main structure and cannot be moved. > > >At 08:31 AM 8/24/2011, you wrote: >>Does the loss of 30 psi include the friction and the elevation loss? If >not, then you are getting pretty close to having cavitation at the pump >inlet and/or collapsing the supply pipe. >> >>Can you put the pump house lower on the hill? >> >>Matt Grisé PE*, LEED AP >>Sales Engineer >>Alliance Fire Protection >>130 w 9th Ave. >>North Kansas City, MO 64116 >> >>*Licensed in KS & MO >> >>913.888.0647 ph >>913.888.0618 f >>913.927.0222 cell >>www. AFPsprink.com >> >> >>-----Original Message----- >>From: [email protected] >[mailto:[email protected]] On Behalf Of Todd Williams >>Sent: Wednesday, August 24, 2011 7:21 AM >>To: [email protected] >>Subject: Minimum pressures in water supply >> >>I am working on a new school project, where the building is 65 ft above the >water supply in the road and 760 ft horizontally. The water supply is >54-46-1130. There is a pump planned, which I have to size. The total >pressure loss in the underground between the supply and the pump house is >approximately 30 psi. I know the general consensus (and some water company >requirements) is that the water pressure not be drawn down below 20 psi. A >500 gpm at 60 psi pump would be a good fit for this project, but the suction >pressures at the pump would end up being below 20 psi. The supply in the >public mains would remain above 20 (due to the elevation), but would be >below that in the private main at the pump room. Any thought if this would >be acceptable? >> >>Todd G. Williams, PE >>Fire Protection Design/Consulting >>Stonington, CT >>860.535.2080 >>www.fpdc.com >> >>_______________________________________________ >>Sprinklerforum mailing list >>[email protected] >>http://fireball.firesprinkler.org/mailman/listinfo/sprinklerforum >>_______________________________________________ >>Sprinklerforum mailing list >>[email protected] >>http://fireball.firesprinkler.org/mailman/listinfo/sprinklerforum > >Todd G. Williams, PE >Fire Protection Design/Consulting >Stonington, CT >860.535.2080 >www.fpdc.com > >_______________________________________________ >Sprinklerforum mailing list >[email protected] >http://fireball.firesprinkler.org/mailman/listinfo/sprinklerforum > >----- >No virus found in this message. >Checked by AVG - www.avg.com >Version: 10.0.1392 / Virus Database: 1520/3853 - Release Date: 08/23/11 > >_______________________________________________ >Sprinklerforum mailing list >[email protected] >http://fireball.firesprinkler.org/mailman/listinfo/sprinklerforum Todd G. Williams, PE Fire Protection Design/Consulting Stonington, CT 860.535.2080 www.fpdc.com _______________________________________________ Sprinklerforum mailing list [email protected] http://fireball.firesprinkler.org/mailman/listinfo/sprinklerforum
