Smart questions
Smart answers
Smart people
Join Eng-Tips Forums
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Member Login




Remember Me
Forgot Password?
Join Us!

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips now!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

Join Eng-Tips
*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.
Jobs from Indeed

Link To This Forum!

Partner Button
Add Stickiness To Your Site By Linking To This Professionally Managed Technical Forum.
Just copy and paste the
code below into your site.

Will007 (Civil/Environmental) (OP)
15 May 08 12:29
I have been told by the city that I need to design sewer pipes flowing half full to have a minimum of 2 fps velocity.  

Is this standard practice, or does anyone know what the min. & max flow velocities are for sewer pipes.

Sizes 8-15" inside diameter.

Thanks in advance for any help.  
RWF7437 (Civil/Environmental)
15 May 08 13:26
Yes, this is standard practice in many areas. 2 ft/sec is considered to be a self cleaning velocity and has been adopted by many, if not all, sewer agencies.

Maximum velocity is not so standardized, in my experience. Somewhere around 10 ft/sec is common practice. Higher velocities lead to problems of water hammer, erosion, gas release (H2S), etc.

You might look at ASCE's Manual of Practice. No. 9 or the Ten State Standards as widely cited authorities.

good luck

 
redbridge (Civil/Environmental)
15 May 08 13:55
I have always been told 2 fps full flow.
Will007 (Civil/Environmental) (OP)
15 May 08 14:15
So the minimum velocity is 2 fps, rather the pipe is flowing full or half-full.

Thanks
Maury (Civil/Environmental)
15 May 08 15:38
I have always designed for a minimum velocity of 2 fps for sanitary sewers and 3 fps for storm sewers.  The velocity will be same whether the pipe is full or half full.
LCruiser (Civil/Environmental)
15 May 08 18:54
Maury -
That is if you are ignoring inlet and outlet conditions - a dangerous practice...
bimr (Civil/Environmental)
15 May 08 19:06
The ususal practice is to design the slopes for sanitary sewers to ensure a minimum velocity of 2 ft/sec with flow at one-half full or full depth. However, a mean velocity of 1 ft/sec is usally suficient to prevent solids deposition. The minimum and maximum velocities are typically specified in state and local standards.

In general, maximum mean velocities of 8 to 10 ft/sec at the design depth of flow will not damage the sewer.

However, high velocities in small pipe sewers and corresponding low depths of flow may allo larger objects, which at times enter all sanitary sewer systems to remain on the inverts, where they may become lodged so firmly that the next rush of wastewater will not detach the objects.

 
Hoagie (Civil/Environmental)
16 May 08 10:16
2 fps is the minimum, 3fps is recommended (Merritt); 10 fps is your upper limit (Ibid). Be sure to check low-flow conditions (with Mannings).


PipelineTZM (Civil/Environmental)
25 Aug 08 7:50
The mostly used minimum self-cleaning velocity for sewer lines is 0.76m/s (metric)
hokie66 (Structural)
25 Aug 08 8:48
.76, that's a nice round number.  So somebody couldn't decide whether it was to be 2fps or 3fps, used 2.5, then converted to metric.  Very scientific.
Helpful Member!  rconner (Civil/Environmental)
26 Aug 08 16:01
I believe I have seen that some authors over the years have indicated that it may take at least a little more than the oft quoted "minimum" velocity to move particularly large "grit" etc. (if this could be an issue) in particularly large sized sewers.  If you did a search e.g. under "critical shear stress sewers" you would proably find more information (e.g. see page 74 at   ftp://phoenix.gov/pub/payf/wtrstndrds.pdf ).   

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!

Back To Forum

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close