Believe me, air does not soften the surge. I ran tests a few years back, the article is in Sprinkler Age (maybe 2003 timeframe). We used one of those pull behind pumps to introduce a sudden pressure surge. We had a hand tightened grooved coupling (which amazingly passed a hydro test with no leaks). The tests that were filled completely with water barely moved. Once we introduced air in the system, the piping network jumped and the coupling separated from the pipe. Air is a big issue with surges.
Duane Johnson, PE Program Manager Division of the Fire Marshal (Support Contractor) Office of Research Services National Institutes of Health 301-496-0487 "Protecting Science - One Sprinkler at a Time" -----Original Message----- From: Cahill, Christopher [mailto:[email protected]] Sent: Tuesday, March 27, 2012 2:52 PM To: [email protected] Subject: RE: Excessive pressure hydraulic ram effect Except if the City main is going over pressure even bleeding off the air won't help. If you have say 200 psi in the lead-in to the building you have 200 in the system air or no air. The difference in air is how many molecules of water actually flow. No air maybe a couple, air, certainly a whole bunch. The air problem is more related to false alarms. If there is enough air the flowing water from the pressure increase is enough to trip the switch, ie many molecules actually move into the compressed air space. In theory air should actually lower surge pressure by acting as a spring to soften the velocity and corresponding pressure spike when the flowing mass of water hits the end of the system. That's essentially what a surge suppressor is that military (hangars) likes. They are nothing more than a trapped air source to absorb a sudden change in pressure and smooth out the spike. Also used on anti-freeze system because they should have no air in them and the delta on the temperatures is easily over 100 degrees in most parts of the US. I have tracked down at least one of these and showed the City they were getting in excess of 250 psi on the lead-in. So about all we could do is put in a PR(elief)V. City was unable to figure out the cause of the pressure. But the PRV solved the building problem, sort of. Sort of because first there was ice then getting caught open because of grit getting caught in the valve seat. As someone else already said bleeding off the air hurts if it's a temperature problem. Well if you have air the source probably isn't temperature in the first place. You have to find the cause before you can apply the right solution. I'd get a recording pressure gauge (make sure it samples in like 1/10 of a second range) and put in on the city side of the riser and a recording temperature gauge in the building. Watching them for a couple days or longer should tell you where the problem is. Chris Cahill, PE* Senior Fire Protection Engineer, Aviation & Facilities Group Burns & McDonnell 8201 Norman Center Drive Bloomington, MN 55437 Phone: 952.656.3652 Fax: 952.229.2923 [email protected] www.burnsmcd.com Proud to be one of FORTUNE's 100 Best Companies to Work For *Registered in: MN -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Johnson, Duane (NIH/OD/ORS) [C] Sent: Tuesday, March 27, 2012 1:17 PM To: '[email protected]' Subject: Re: Excessive pressure hydraulic ram effect For surges, bleed off the air and provide a check valve. For slower increases, provide relief valve as others have stated. ----- Original Message ----- From: Ford, Charles [mailto:[email protected]] Sent: Tuesday, March 27, 2012 11:11 AM To: [email protected] <[email protected]> Subject: RE: Excessive pressure hydraulic ram effect Has anybody come up with a permanent fix for recurring high pressure on wet pipe systems. This is believed to be caused by the ram effect. Regards C. Burton Ford Nicet Certified Special Hazards IV Fire alarm IV Sprinkler III Water Based Inspections I NFPA Certified Fire Protection Specialist [CFPS] Cintas Fire Protection 1038 Conshohocken Road Conshohocken ,PA 19428 610-233-1400 Fax 610-233-1401 ________________________________________ This e-mail transmission contains information that is intended to be confidential and privileged. If you receive this e-mail and you are not a named addressee you are hereby notified that you are not authorized to read, print, retain, copy or disseminate this communication without the consent of the sender and that doing so is prohibited and may be unlawful. Please reply to the message immediately by informing the sender that the message was misdirected. After replying, please delete and otherwise erase it and any attachments from your computer system. Your assistance in correcting this error is appreciated. _______________________________________________ Sprinklerforum mailing list [email protected] http://fireball.firesprinkler.org/mailman/listinfo/sprinklerforum _______________________________________________ Sprinklerforum mailing list [email protected] http://fireball.firesprinkler.org/mailman/listinfo/sprinklerforum _______________________________________________ Sprinklerforum mailing list [email protected] http://fireball.firesprinkler.org/mailman/listinfo/sprinklerforum _______________________________________________ Sprinklerforum mailing list [email protected] http://fireball.firesprinkler.org/mailman/listinfo/sprinklerforum
