Maximum allowable velocity in public water mains??? 1

[harboe]

I have a site with a several fire hydrants and a 50,000sf building on site and the client is requiring that the maximum allowable velocity in the site water lines be kept at 10fps or less. Is this typical practice to use this as a limit for on site fire and water lines?

 

[BigInch]

Its very typical for most all pipe flows where pressure drop over long lengths is of concern. It also limits erosion from foreign particles being carried along with the flow. Many projects also require a minimum velocity of 3 ft/sec to help in keeping foreign particles from settling and accumulating in low spots.

The maximum velocity might be increased (if allowed by your project specs) over short lengths of pipe, near pumps or other equipment, as long as the pressure drop is tolerable.

One caution. Approaching or exceeding 10 fps may increase the likelyhood of hydraulic surges.

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[bimr]

From the military civil engineering guideline:

Try:

http://www.usace.army.mil/inet/usace-docs/eng-manuals/em1110-1-4008/c-3.pdf

For normal liquid service applications, the acceptable ft velocity in pipes is 2.1 ± 0.9 m/s (7 ± 3 ft/s) with a maximum velocity limited to 2.1 m/s (7 ft/s) at piping discharge points including pump suction lines and drains. As stated, this velocity range is considered reasonable for normal applications. However, other limiting criteria
such as potential for erosion or pressure transient
conditions may overrule. In addition, other applications
may allow greater velocities based on general industry
practices; e.g., boiler feed water and petroleum liquids.

 

[rconner]

You may be interested also in various references in the past thread at

http://www.eng-tips.com/viewthread.cfm?qid=132053

(it appears for whatever reason many authorities for get some nervous with certain piping materials at variable velocities beyond say 1 or 2 m/s (3-7 fps)).

 

[AegisFPE]

The Washington State Department of Health (DOH) recommends a maximum velocity of 8fps, but permits greater velocities during fire flow conditions. This may be a way to address your concern.

"8.1.6 Maximum Velocity:
The DOH recommends that the design of distribution mains not exceed a maximum velocity of eight (8) feet per second (fps) under PHD conditions, unless otherwise specified by the pipe manufacturer. Maximum velocities of greater than eight fps may occur under fire flow conditions, for short sections of mains, or for piping within pump and valve station facilities. Long sections of mains with higher velocities should be checked for transient (water hammer) conditions. Refer to Section 8.1.8 for discussion on surge control and Section 8.2.4 for modeling transient conditions." -

http://www.doh.wa.gov/ehp/dw/DesignManual/chapter_8.DOC

 

[BigInch]

Nice link. Got the Table of Contents link by any chance?

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[CarlB]

Found full manual at

http://www.doh.wa.gov/ehp/dw/publications/design.htm