I heard the collapse story as well. However, I have yet to figure out how a +20 psi pressure can cause a pipe to implode with a normal depth of bury soil pressure. My guess is that is actually a safety factor to prevent main pressure from creating a vacuum and causing back siphoning.
At 10:16 AM 8/24/2011, you wrote: >During a sprinkler design class we were told by the instructor that the 20psi >comes from the health department and anything less than 20psi in the mains >will require citizens to boil the water to remove containments in the water. >Previously I had always heard anything less than 20psi could potentially >collapse water lines. > >Steve > >-----Original Message----- >From: [email protected] >[mailto:[email protected]] On Behalf Of David de Vries >Sent: Wednesday, August 24, 2011 8:11 AM >To: [email protected] >Subject: Minimum pressures in water supply; Why 20 psi? > >Does anyone know where the 20 psi minimum for undergound piping originated? I >have seen it in some state water regs, but have never been satisfied that it >is a sound, scientifically-based number. > >I have also seen fire dept SOP's set an alert on suction pressure at the >pumper to 5 psi. Depending on the hose lay, that might equate to 20 (or 10) >psi in the main. > >Dave > >David A. de Vries, P.E., CSP >Firetech Engineering Incorporated > > >--- On Wed, 8/24/11, Letterman, Todd <[email protected]> wrote: > > >From: Letterman, Todd <[email protected]> >Subject: RE: Minimum pressures in water supply >To: [email protected] >Date: Wednesday, August 24, 2011, 8:27 AM > > >I agree with all who have responded and I'm not sure if there is hydrant >at the entrance to this place or along the street that could rob your >suction pressure. If there is a hydrant coming into the property, then >they are most likely going to start there hose lay at that point, which >may rob all the theoretical values so far. You are not going to have >much suction pressure at a 100%. If a fire takes it to that demand but >there is really nothing stating that you cant go lower than 20 unless >the water authority or other entity states other wise. It was never >stated if it is going to be a Electric or Diesel Driver or have you >gotten that far yet? > >Todd Letterman >Fire Prevention Engineer CFPS >Riverside County Fire Department "Fire never sleeps" >(951) 955-5273 FAX (951) 955-4886 >[email protected] > > >-----Original Message----- >From: [email protected] >[mailto:[email protected]] On Behalf Of Todd >Williams >Sent: Wednesday, August 24, 2011 5:21 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 >-------------- next part -------------- >An HTML attachment was scrubbed... >URL: ><http://fireball.firesprinkler.org/mailman/private/sprinklerforum/attachments/20110824/0eebc788/attachment.html> >_______________________________________________ >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
