Typical pipes used for municipal water distribution 4

[amrbekhit]

Hello all,

I'm working on a project where I will be designing instrumentation that will live inside underground water pipes. I was wondering if anyone knew the typical sizes of such pipes, the types of junctions used, and typical pressures and flows inside them. Do these properties vary from country to country (I live in the UK)?

Thanks

--Amr

 

[bimr]

The minimum pipe size for modern municipal water distribution systems in the US is 8". The pipes are typically made from PVC or ductile iron. The piping is considered to be flexible with belled slip joints. Internal water pressures are typically between 40-70 psig. Flow velocities are typically 3-5 ft/sec.

 

[coloeng]

bimr said "The minimum pipe size for modern municipal water distribution systems in the US is 8"."

This is true where fire protection is provided. The pipe is some distribution systems can be as small as 2-inch, but is typically no less than 4-inch.

bimr said "Internal water pressures are typically between 40-70 psig."

This is probably true in areas that have moderate to little elevation differences. In more mountainous areas the pressures can range from 30 to over 200 psig.

 

[cvg]

In United States:
2 and 4 inch distribution piping is not typical and should be considered substandard. insurance requirements require adequate water and pressure to fight fires which generally requires 8 inch minimum pipes in a looped system. Larger systems may use steel or concrete cylinder pipe and pvc (in my experience) is used much less often. Most systems I have worked with range from 40 - 120 psi, even in mountainous regions.

Not sure what "type of junctions" is referring to.

Flow rates are usually designed to limit velocity between 5 - 10 feet/second in the pipe except during fire flows where velocities may be higher.

 

[semo]

I'll tend to disagree with CVG and Bimr on the minimum size here too. It all depends upon the system.

Rural areas will tend to have more 2" & 4" pipe. Not adequate at all for fire protection; but, for domestic use it can be adequate.

In rural county water districts the pipe should be sized based upon the flow needed. Excessively sized pipes allow for excessive detention times and can cause a reduced chlorine residuals, tastes and odors and other bacterial growths as the water stagnates.

It also causes higher installation costs and water bills when you are installing 120 miles of pipe in a district.

In a Municipal setting, I'll agree that they are too small.

 

[cvg]

In some small rural systems, perhaps 2 inch piping is an accepted standard. Where small pipes were installed in rural water districts I have worked with, they were old, leaking, corroded and substandard for both pressure and flow. These districts had a replacement program for these pipes with 8 inch minimum. I have designed literally miles of 8 - 12 inch replacement pipe for these small rural systems.

I feel these "rural" systems with small piping are not typical of the vast majority of water distribution systems in the united states and are the exception, not the rule. And defending BIMR (although I feel he can defend himself adequately) in "modern municipal water distribution systems" - 2 and 4 inch piping is definitely not the standard.

 

[dicksewerrat]

What kind of instruments? How will you get data from them?

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[amrbekhit]

Thank you all for the useful information so far.

@dicksewerrat: The instruments will hopefully include things like a camera, ultrasound modules, flow and pressure meters, although at the moment I am focussing on the vessel that will carry them.

--Amr

 

[amrbekhit]

Here's a related question: does the water in municipal pipes ever stop flowing?

 

[cvg]

only sometimes when the valves are closed

 

[bimr]

The water distribution system is typically a complex maze containing pumps, storage elements, and pipelines of a variety of sizes. Special techniques of network analysis are used to determime water flow patterns. Depending on where the water enters and exits the maze, the water flow may stop or even reverse dirction.

 

[redbridge]

2" and 4" water lines are very common and are still installed today in rural areas. If you have 12" and 8" water lines serving a small population spread out over a county then you will have water quality issues.

 

[rconner]

For whatever it is worth,

AWWA Manual M31, Distribution System Requirements for Fire Protection (3rd edition 1998) included substantial discussion of “Fire Flow Requirements” and also contained the verbiage, “…meeting requirements for minimum pipe sizes (e.g. 6-in. [150-mm] pipes in loops and 8-in. [200-mm] dead ends) in neighborhood distribution mains when much smaller pipes would suffice for delivery of potable water only.”


The “Ten States Standards” (Recommended Standards for Water Works) 2007 Edition under section 8.2.2 Diameter included,

“The minimum size of water main which provides for fire protection and serving fire hydrants shall be six?inch diameter. Larger size mains will be required if necessary to allow the withdrawal of the required fire flow while maintaining the minimum residual pressure specified in Section 8.1.1.

The minimum size of water main in the distribution system where fire protection is not to be provided should be a minimum of three (3) inch diameter. Any departure from minimum requirements shall be justified by hydraulic analysis and future water use, and can be considered only in special circumstances.”


NFPA 24 Standard for the Installation of Private Fire Service Mains and Their Appurtenances (1995 edition) contained, “Adequacy of water supply shall be determined by flow tests or other reliable means…” and “…Public mains shall be ample size, in no case smaller than 6 in. (152 mm).”


While as others have quite eruditely stated there might be some new construction with perceived scopes outside these particular standards of care that allow smaller pipes; however, about the only other thing I would add is that there are quite large quantities of 6” and particularly smaller water distribution piping now being replaced at substantial cost/ at least in the United States (much with 8" and larger pipes), not necessarily that they are unsuitably ag(e)ing [perhaps the most popular perception] or not providing cost-effective service, but instead due to the fact they simply cannot (with encountered burgeoning growth etc.) provide the level of flow that is now deemed necessary for now developed areas.
I guess virtually all those original designers also thought the pipes they specified would be large enough for their lives as well (many originally quite "rural" areas have quite rapidly become quite developed)! [Incidentally, if anyone is aware that any of this standards etc.verbiage has changed in more recent versions, feel free to post the latest).



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