Maximum water velocity (NFPA13)
Maximum water velocity (NFPA13)
(OP)
Hi Guys & Gals
What is the maximum permissible water velocity in sprinkler pipes?
What is the maximum permissible water velocity in sprinkler pipes?
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Maximum water velocity (NFPA13)
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Maximum water velocity (NFPA13)Maximum water velocity (NFPA13)(OP)
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RE: Maximum water velocity (NFPA13)
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NFPA 13 doesn't contain velocity limits because the Committee on Automatic Sprinklers has long felt that piping velocities are self limiting. The pressure losses increase exponentially as velocities increase, so pipe sizes must be increased to make use of available water supply pressures. The committee also believes that hydraulic calculation inaccuracies using Hazen-Williams are minor compared to the inaccuracies associated with assuming a long-term pipe roughness factor. In one 1968 study of actual roughness of aged steel pipe, the measured C values ranged from 82 to 135.
RE: Maximum water velocity (NFPA13)
Regards
Dave
RE: Maximum water velocity (NFPA13)
RE: Maximum water velocity (NFPA13)
I've been told 32 fps is the upper limit to avoid water hammer. I'm skeptical as to the credulity of this statement and haven't been able to find a proof sufficient for me to make the statement myself. Nonetheless no calcs leave here exceeding 32 fps. Might be an old wives' tale.
RE: Maximum water velocity (NFPA13)
RE: Maximum water velocity (NFPA13)
Thanks for the update.
RE: Maximum water velocity (NFPA13)
FM used to have the velocity requirements - dropped them.
NFPA used to have the velocity requirements - dropped them.
Water hammer can happen if you have a quick start fire pump.
Our specs stated 30 ft/s but when I asked where it came from - nobody could tell me.
I now subscribe that I want low as possible velocities but if required, I will take what the system will take.
If I damage a piece of equipment, but put out the fire - I will accept that.
RE: Maximum water velocity (NFPA13)
Irrespective of such issues as survivability of exposed pipes or increased toxics or dangers in combustion etc., I believe many other authorities, manuals and specifications etc. do suggest limitation of flow velocity in at least plastic pipes (see even article it appears promoting some use of plastic pipes at http://
While I guess I also understand the premise of the tradeoff, "...damage a piece of equipment, but put out the fire - I will accept that", it would appear that a delivery pipeline splitting near immediately due to shock in a "water hammer" event would probably not help much with the latter objective.
RE: Maximum water velocity (NFPA13)
I have yet to use it on a commercial project. Not many owners have indicated a preference for it.
Water hammer is caused by either a rapid stopping or rapid starting of water floo.
If a sprinkler system is on "city pressure" - I don't see a rapid flow start. A sprinkler or two goes off and you have 20-30 gpm starting to flow. At the larger flow in a 1" pipe, that would be ~14 fps - not excessive.
If the system is on a fire pump system - and the pump does not have a soft start or ramp up starting mode - then you could have excessive speeds and potentially water hammer.
I don't understand why fire pumps in new construction are specified without a ramp up function.
Where I have seen high flow velocities or others have seen them is,
1. When the sprinkler contractor is just putting numbers in his software program without understanding the real situation (i.e. trying to put 700 gpm through a 2.5" pressure regulating valve off a 6" standpipe because that is the only size the valve comes in)
2. When the sprinkler contractor is trying to use the smallest piping he can to keep his cost down - even though the velocities will be in the 30-40 fps range.
RE: Maximum water velocity (NFPA13)
The IPC has maximum velocities:
all piping 1/2 inch or smaller = 5 feet/sec.
copper, 5/8" - 1-1/4" = 5 feet/sec.
CPVC, 5/8" - 1" = 8 feet/sec.
Galvanized, 5/8" - 1-1/2" = 8 feet/sec.
Polyethylene, 5/8" or larger 8 feet/sec.
Polybutylene, 5/8" - 1" = 8 feet/sec.
PVC, 5/8" - 1" = 8 feet/sec.
RE: Maximum water velocity (NFPA13)
It helps minimize erosion of the pipe fittings.
But if a designer limited sprinkler piping to those velocities, the piping would be vastly oversized.
RE: Maximum water velocity (NFPA13)
There's a bit of a fallacy in that reasoning however. Specifically a sprinkler designer doesn't know how many sprinklers will activate should a fire start. If all sprinklers in an auditorium open (just thinking here) then the system's effectiveness would be little on a fire with sufficient fuel loads. If only a single sprinkler opens in a small compartment, statistical data suggests one sprinkler can often extinguish a fire in a small compartment considered light hazard or residential. Designing for the upper limit makes sense in a worst case scenario (such as a fire is anyways).
Why fire pumps are not designed to ramp up pressure is beyond me and I haven't found a reason. I have seen underground loops blown out by water hammer from testing of fire pumps. Also mains on the suction side have been collapsed, which may have been avoided if the pump ramped up and gave more time for pressures to equalize.
To PEDDARIN2, the advantage of using CPVC piping is not necessarily its friction or mechanical properties relating to calculations but to its being able to be cut and fitted in the field. Residential construction (homes, motels, etc) and most stick frame tends to be very sloppy if one is accustomed to steel buildings. If such construction would be protected by steel piping then even a very good field survey would require many hours of cutting and threading steel pipe on the job site to make it fit properly. The greatest downside is when a fitter omits to glue a joint and it blows out six months or a year after the job is finaled.
RE: Maximum water velocity (NFPA13)
Good point
Purple star for you
RE: Maximum water velocity (NFPA13)
Instead of $40,000 we'd easily be $120,000 and that wouldn't be the cost of materials, I am not even sure material would go up and even if it did it wouldn't be all that significant, but labor would go through the roof. Owners are watching price now more than ever.
RE: Maximum water velocity (NFPA13)
As stated, I haven't done any plastic sprikler piping - yet.
Some of it is the owners haven't requested/required it. Another is that there is some quirkiness in the 25/50 smoke and flame spread rules that keeps it out in a plenum area.
On my projects, there is no field cutting of the piping. I get a sprinkler layout drawing to review. From that I can check various things about the proposed layout. Once this is reviewed (by me and the AHJ) and approved (by the AHJ) - piping is cut to match the plans and sent out to the field so the installer just has to put the pieces together in order.
When you mention a glue joint failing months or a year after completion - isn't there some requirement for a pressure test on the system?
It might not be required on residential but I require it on my projects. A joint that is not good or a weld that is incomplete shows up during this test - so I don't have to worry about it failing if there is a fire.
RE: Maximum water velocity (NFPA13)
Sure, good designers will minimize the amount of field cutting, but it is rare to see any job where the Rigid 300 does not get turned on.
Have a great day!
Travis Mack
MFP Design, LLC
www.mfpdesign.com
RE: Maximum water velocity (NFPA13)
But, if there is a lot of it, the permit drawings (showing lengths of piping, elevations, etc.) the sprinkler contractor is supposed to be building to have to be modified and the permit has to be reapplied.
After a couple of those, the HVAC or the plumbing contractor has to make it work to get around the sprinkler piping.
RE: Maximum water velocity (NFPA13)
Personally I've only seen one come loose months after the job is done, but it only takes one to understand how many dollars' worth of damage is done.
RE: Maximum water velocity (NFPA13)
RE: Maximum water velocity (NFPA13)
the maximum velocity in fire fighting piping is 20 ft/sec as NFPA 20
and 35 ft/sec in inspection,test and stationary pumps as NFPA1963
ANY QUESTION ?
I AM READY FOR HELP
RE: Maximum water velocity (NFPA13)