×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • 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!
  • Students Click Here

*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.

Students Click Here

Jobs

Minimum sewage pipe slope

Minimum sewage pipe slope

Minimum sewage pipe slope

(OP)
What is the minimum slope one can use on a sewage system with less than 25 fixture units?

I know that 1% is acceptable and sometimes 2% is the least recommended...
can you use on that system a pipe with 0.5% slope?

And let say i used the manning formula to see if a given slope is acceptable..how should i analyze the answer? should the velocity be below 6fps ?

RE: Minimum sewage pipe slope

That depends on if you are inside a building or outside.

Inside slopes are determined by the applicable plumbing code.

In the IPC world, 25 fixture units would be 3 or 4", depending on what type of drain (building drain or branch). At that pipe size, minimum pipe slope is 1/8" per 1 foot, which is ~1.04%

Outside slopes are typically determined by expected flow rates and maintaining at least 2 fps velocity. Personally, with 25 fixture units, I would not go less than 1%, but sometimes the minimum outside pipe size is 6" so you might need to be at 2% to maintain velocity.

RE: Minimum sewage pipe slope

(OP)
i'm talking about an outside sewage pipeline...with a diameter of 200mm... can you explain why using formulas or by referring to international codes?

RE: Minimum sewage pipe slope

You need 2.5-3 fps to keep all the solids suspended. Use Manning's equation.

Richard A. Cornelius, P.E.
WWW.amlinereast.com

RE: Minimum sewage pipe slope

Failure to maintain the proper velocity in the pipeline will allow the solids to drop from suspension. This will result in the pipline filling and pluging with heavy slurry solids requiring significant work to clean. The reason that sewage wastes rule of thumb is 1 to 2% is that it works. Slopes outside of this range will result in solids seperation and cause pipe pluging. In the end, there are no good reasons to ever design a gravity drain system without proper slope

RE: Minimum sewage pipe slope

(OP)
thank u guys...but i found the answer while reading ASPE...the minimum velocity should be 2fps as dicksewerrat said..and using the manning formula or any of the two other formulas u can get the minimum required slope..which would be 0.4% but aspe recommends it to be 0.5%

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

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!


Resources