Gentlemen and /or Ladies: The restriction on velocities was introduced by FM back when grids first came into use. Automatic and Grinnell in years past always used a maximum velocity of 32 fps that came from some old studies of water mains. When grids first started, contractors, and I was one, immediately started pushing the envelope with 1" grids all over the place. FM decided that to use the 20 fps requirement on grids. Later they modified the requirement to apply to the branch line but not the riser nipples. There has never been a requirement for a maximum velocity in NFPA 13 to my knowledge. The hydraulic formulas and the C factors have a safety factors built in. Of more importance in a lot of cases is the reliability the water supply and the accuracy of the water test used in the calculations. Water tests and water supplies are often the least researched part of the design. In many parts of the country the AHJ's impose a limit by insisting on a cushion of some kind. It parts of Florida the AHJ's do not allow more than 50 psi static pressure to be used in the calculations period regardless of the water test results. It seems to me that you may be gagging on a nat and swallowing an elephant. If you are concerned specify a cushion be allowed and do not calculate the demand to the maximum available water supply. Specify a particular psi cushion.
If you want a system to last forever just specify Schedule 40 pipe and do not allow thin wall pipe but the cost of the system will go up and the owner may not be happy that he has to pay more. Michael L. Brown -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of George Church Sent: Monday, January 15, 2007 2:26 PM To: [email protected] Subject: RE: max velocity Given the long life and "who knows what may happen" alterations, you're using velocity as a built-in hedge against -well-who knows? But consistently applied, you'll end up mtg the criteria important to the owner- trying to make a system that's as idiot-proof as possible. Do you also limit spacing? If walls are going to be added, it makes it handier for those who don't have pilot hole clamps and snaplets to add heads if there's an outlet with 5'. It is a pain to go in and change wet systems to C=100, and an alternative method would be to simply specify a larger cushion, either in % or 20 PSI. Perhaps tailor it to the building and what characteristics the servicing water purveyor has, whether it's a mature area, or growing wildly so expectations would be that it'll be degrading quickly. But with a 50 year life- that's hard. As my friend Steve pointed out, did anyone think bottled water would be a zillion dollar a year industry several years ago? Heck, that's almost as long as Thom's been in sprkrs! glc -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of [EMAIL PROTECTED] Sent: Monday, January 15, 2007 1:55 PM To: [email protected] Subject: RE: max velocity Folks, Here is some more food for thought. I provide the sprinkler specification for all of my federal projects. I use 20 fps velocity as a limit and a maximum C of 100 to insure that I have a system that has a chance to last for the life of the building (approximately 50+ years). Our buildings are always being changed with the sprinkler system being drained and modified many many times by all sorts of contractors, from the best to the worst. Once the building is constructed and occupied, the local GSA service center does all of the work in the building, usually with the lowest bidder. Therefore, we need some sort of hedge against all of this. Once the building is built, it is out of my control. I see no problem specifying these limits as long as everyone is bidding the same job. Any suggestions? Thank You Rahe Loftin, P.E. Region 7 - GSA Office - 817-978-7299 Fax - 817-978-8644 Cell - 817-371-3102 _______________________________________________ Sprinklerforum mailing list [email protected] http://lists.firesprinkler.org/mailman/listinfo/sprinklerforum _______________________________________________ Sprinklerforum mailing list [email protected] http://lists.firesprinkler.org/mailman/listinfo/sprinklerforum _______________________________________________ Sprinklerforum mailing list [email protected] http://lists.firesprinkler.org/mailman/listinfo/sprinklerforum
