intermittent high velocities during fire flows
intermittent high velocities during fire flows
(OP)
I have a project that was supposed to have a 16" watermain in front of the development. It turns out that the watermain is under a major roadway and is really deep. There is a hydrant in front of the development that we are considering taking
off and extending a 10" main into the development. The hydrant line is 6" in diameter, 20 ft long and connects to the 16" main under the road. The pressures and flows from the flow test will produce a 20 fps velocity through the 6" main ONLY during fire flows. Is the high velocity in the 6" main a major concern since it's just for fire flows, it's a short run and there are no bends?
off and extending a 10" main into the development. The hydrant line is 6" in diameter, 20 ft long and connects to the 16" main under the road. The pressures and flows from the flow test will produce a 20 fps velocity through the 6" main ONLY during fire flows. Is the high velocity in the 6" main a major concern since it's just for fire flows, it's a short run and there are no bends?





RE: intermittent high velocities during fire flows
RE: intermittent high velocities during fire flows
RE: intermittent high velocities during fire flows
RE: intermittent high velocities during fire flows
Richard A. Cornelius, P.E.
WWW.amlinereast.com
RE: intermittent high velocities during fire flows
LIMITING WATER VELOCITIES IN THERMOPLASTICS PIPING SYSTEMS
The maximum water velocity in a thermoplastic piping system depends on the specific details of the system, the character of the flow stream, and the system operating conditions. In general, design velocities of 5 to 10 feet per second are being used and are considered normal.
Higher flow velocities are common in certain applications including gravity and slurry flow. However, in all instances, careful consideration should be given to the effect that flow velocity will have on overall piping system performance in light of valve, pump, and system operation. Particular attention should be given to possible effects of excessive velocity on pipe abrasion rate
and on pressure surges that may be generated by sudden or rapid changes in flow velocity. Recommendations for pressure surge design, which are given in design standards or offered by piping manufacturers, should be followed.
In the case of a polyethylene piping system, the working pressure of the system plus recurrent surge pressure associated with a specific piping arrangement or operation should not exceed 150% of the pipe pressure rating. Occasional surge pressures in excess of this limit are allowable so long as the total of the expected surge plus the working pressure of the system does not exceed 200% of the pipe pressure rating.
AWWA Standard for Polyethylene (PE) Pressure Pipe and Fittings, 4 in. through 63 in., for Water
Distribution, C-906, American Water Works Association, Denver, CO, 1990.
http:/
RE: intermittent high velocities during fire flows
RE: intermittent high velocities during fire flows
What are the required fire flows for what duration for you development ?
Will the ten inch line be looped back to the 16-inch line or to some other line or lines in the existing distribution system ?
Are there significant elevation differences across your development ?
If the six inch line failed, say because of water hammer, what would be the consequences ?
RE: intermittent high velocities during fire flows
The required fire flow is 1500 gpm.
No, the line will not be looped back to the existing main.
There are no significant elevation changes.
The development would be without water until the main is fixed.
Thanks
RE: intermittent high velocities during fire flows
Since it's a short run (less than a full joint) and if it has good rodding or restrained joint DIP I think I'd be OK with it. I worked on a pump station that had a short piece of 12" DIP operating around 20 FPS, it was only a few feet in length but was above grade and flanged.
Restraint would be the key. I'd have a good thrust collar poured at the transition from the existing 6" to the 10".
Did you actually do a flow test from the hydrant to verify you will get your 1500 GPM? If so you've already tested the line at that kind of velocity. Most if not all hydrants are connected to the mains with 6" pipe, so it's not really that uncommon to scream water through a short 6" run.
RE: intermittent high velocities during fire flows
Thanks
RE: intermittent high velocities during fire flows
The needed fire flow is usually developed by the ISO or the fire chief and depends on the type of building and the building size.
http://www.isomitigation.com/downloads/ppc3001.pdf
You have not stated what type of development that you have. If your development consists of a Walmart, you will need 3000 gpm.
You need to be sure that you design for the correct fire flow.
RE: intermittent high velocities during fire flows
RE: intermittent high velocities during fire flows
RE: intermittent high velocities during fire flows
That would only be around 11 feet/sec fire flow.
RE: intermittent high velocities during fire flows
RE: intermittent high velocities during fire flows
Online Link to the California Fire Code (based on IFC):
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RE: intermittent high velocities during fire flows
I hope this information is of help in this or at least similar future issues.