Minimum sewage pipe slope 1

[afa13]

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 ?

 

[PEDARRIN2]

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.

 

[afa13]

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?

 

[dicksewerrat]

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

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[psv1990]

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

 

[afa13]

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%