The following two definitions are contained within the FM Data Sheets. As far as I know, the reasoning behind the 32 fps restriction was that it equates to the difference between turbulent and laminar flow of fluids (in this case water) through a piping network. The accuracy of the Hazen Williams equation has been questioned once turbulent flow exists within the piping network. Any other limits are just more or less stringent depending upon the project. Velocities are not limited in NFPA 13, the 32 fps did appear in past editions in the appendix.
Darcy-Weisbach Method: A method of calculating friction loss within a sprinkler system that is based on a given internal pipe diameter, the average velocity of the liquid moving through the pipe, the material make-up of the pipe as well as the viscosity of the liquid moving through the pipe. Although it can be used for any sprinkler system hydraulic analysis, it should be used for any sprinkler system that is not water-based or any sprinkler system where the waterflow velocity exceeds 30 ft/s (9.0 m/s). Hazen-Williams Method: A method of calculating friction loss within a sprinkler system that is based on a given waterflow rate, internal pipe diameter, and internal pipe roughness coefficient. It can be used for the calculation of friction loss through a water based sprinkler system having waterflow velocities not exceeding 30 ft/s (9.0 m/s). See FM Global Data Sheet 3-0, Hydraulics of Fire Protection Systems, for more information on this hydraulic calculation method. Regards, Carl Chappell -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Travis Mack, SET Sent: Friday, June 25, 2010 12:52 PM To: [email protected] Subject: Re: limits on velocity The funny thing with all of this velocity limits is that it is based on a demand calc. The water supply doesn't "know" to throttle the flow so we only get what we calc'd. If I figure all heads in the design area flowing at maximum water supply, then the velocity exceeds their limits, but the demand calc with a 50 psi cushion (due to limiting velocity) will only show a max of 15 fps so it would be approved. I really wonder sometimes if people understand what they are specifying. My customer is trying to fight the limits, but I don't know if he will succeed or not. It is just a crazy Friday. On 6/25/2010 12:30 PM, George Church wrote: > I explain the water doesn't know who underwrites the building, it moves from > areas of high pressure to areas of low pressure follwoing the rules of > nature. > It won't slow down to 15 FPS so why pretend it will? > As Roland's white paper years ago said, the friction loss in high velocity > systems self-regulates the use of high velocity. if you haven't got the > steam to make it go, you can't use it. > If you do have the excess pressure to burn, the watter WILL go that quick so > why not understand that and accept it? > If the EOR doesn't budge because he believes his own thumb, can you ask the > Owner or Owner's rep if the Owner cares a hoot about it since its not in > code and costs him $$$? That will generally get relief. > > I heard FM was trying to stop what was then little G from installing 1" > grids in Acme grocery stores. And I'll agree that if flowing one more head > blows the calc out by 30 PSI, maybe you've pushed a little harder than you > should, and spring for the 1.25". In my slash and burn days in the 80's, > when a 5 PSI cushion was there if you added up the cushion on the three > systems ;) I designed systems that probably woulda gotten speeding tix in > Montana. Protecting my retirement asset, smaller stones. > > We recently did some retrofit and repair work on a large contractor's > systems from the 1970's with big pumps and really really small pipe, bearing > out what I'd heard about the 1' grids. > > glc > > -----Original Message----- > From: [email protected] > [mailto:[email protected]] On Behalf Of Cliff > Whitfield > Sent: Friday, June 25, 2010 2:31 PM > To: [email protected]; [email protected] > Subject: RE: limits on velocity > > Therein lies the problem. I see this all of the time and most are very > reluctant to remove their restrictions. It must come from something they > learned in plumbing or HVAC but the ones I deal with are usually adamant > about keeping it. And boy does it ever make your pipe sizes go up. > > I feel your pain. > > Cliff > > -----Original Message----- > From: [email protected] > [mailto:[email protected]] On Behalf Of Travis Mack, > SET > Sent: Friday, June 25, 2010 1:27 PM > To: [email protected] > Subject: Re: limits on velocity > > The question was asked because a specifying engineer is requiring 15 fps on > all pipes - including existing piping for a 6 story retrofit. The existing > system calculations indicate velocities of 34 fps. :-) > > On 6/25/2010 11:22 AM, Vince Sabolik wrote: > >> ALWAYS WAS rule of thumb. And I got an old thumb... 16 fps for >> underground >> >> >> >> >> Vince Sabolik >> Christi Fire Protection, Inc. >> 11351 Pearl Road >> Strongsville, Ohio 44136 >> >> T 440 572-7730 F 440 572-7719 Email: >> <mailto:[email protected]>[email protected] >> >> _______________________________________________ >> Sprinklerforum mailing list >> [email protected] >> http://fireball.firesprinkler.org/mailman/listinfo/sprinklerforum >> >> For Technical Assistance, send an email to: [email protected] >> >> To Unsubscribe, send an email >> to:[email protected] >> (Put the word unsubscribe in the subject field) >> >> > _______________________________________________ > Sprinklerforum mailing list > [email protected] > http://fireball.firesprinkler.org/mailman/listinfo/sprinklerforum > > For Technical Assistance, send an email to: [email protected] > > To Unsubscribe, send an email to:[email protected] > (Put the word unsubscribe in the subject field) > > _______________________________________________ > Sprinklerforum mailing list > [email protected] > http://fireball.firesprinkler.org/mailman/listinfo/sprinklerforum > > For Technical Assistance, send an email to: [email protected] > > To Unsubscribe, send an email to:[email protected] > (Put the word unsubscribe in the subject field) > > _______________________________________________ > Sprinklerforum mailing list > [email protected] > http://fireball.firesprinkler.org/mailman/listinfo/sprinklerforum > > For Technical Assistance, send an email to: [email protected] > > To Unsubscribe, send an email to:[email protected] > (Put the word unsubscribe in the subject field) > _______________________________________________ Sprinklerforum mailing list [email protected] http://fireball.firesprinkler.org/mailman/listinfo/sprinklerforum For Technical Assistance, send an email to: [email protected] To Unsubscribe, send an email to:[email protected] (Put the word unsubscribe in the subject field) _______________________________________________ Sprinklerforum mailing list [email protected] http://fireball.firesprinkler.org/mailman/listinfo/sprinklerforum For Technical Assistance, send an email to: [email protected] To Unsubscribe, send an email to:[email protected] (Put the word unsubscribe in the subject field)
