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
