Acceptable Reduction in Size for Gravity flow sewer and drain applications 2

[Lostino]

Hello All

We are currently trying to modify the internal couplers on our piping system and one of the solutions is to increase the thickness of the couplers. This will result in a decrease of the pipe OD which will ofcourse have much more effect on the smaller diameters than the larger ones.

If I take the 200 mm pipe for example (ID = 200 mm) what is the maximum reduction that we can make on the joint section so as not to disturb or affect the fluid flow hydraulics. The diameter will return to 200 mm after the joint.

Any help will be much appreciated.

Thanks

 

[Lostino]

I forgot to mention. the pipes are HDPE pipes

 

[jgailla]

Any reduction (or expansion) in pipe size will affect the fluid flow hydraulics.
The question is whether the system will still be adequate for the flow.
There are many ways to analyze the system. For a simple gravity system, try searching wbdg.org for Army Corps methodologies.
If you have an 200mm (8") pipe that is a hundred feet long and reduce the size at one joint by 10%, there is likely no problem hydraulically.
The other issue, which is probably more important, is that if you have a symmetric coupling of a smaller diameter, you are creating a hump in what should be a smooth invert.

 

[Lostino]

Thanks for the reply.

so basically the problem is that sediments could be trapped on the edge of this "hump" if it is large enough. Again, for a 200 mm pipe, what could be this "hump" size that would be just ok?

 

[cvg]

if this is a sanitary sewer, I would not recommend this approach at all.

 

[bimr]

There is no acceptable reduction in pipe diameter for a gravity sewer.

The reduction in size would tend to trap debris, silt, grease, etc. This will lead to material building up over time and causing the fouling and clogging of the sewer.

The coupler should be external not internal.

 

[jgailla]

cvg and bimr are correct as usual.
No reduction in pipe size along the invert is acceptable.

 

[Lostino]

Currently using our joining system, for the 200 mm, the diameter is about 188 mm at the joint and then goes back to 200 after the joint. So this is not suitable for sewer? Also, if only for stormwater, we are looking to make the reduction so that the dia becomes 180 approximately. Any problem with that if it is for stormwater?

Thanks a lot

 

[bimr]

Don't think that any agency or authority that is reviewing your pipe for code compliance will approve it for sewer or stormwater.

 

[jgailla]

I would not do that for stormwater or sewer unless there was an awful good reason.
You haven't said why you are doing this. External couplings for HDPE are readily available.

 

[Lostino]

Its a corrugated HDPE pipe so we dont have a smooth outer surface for the coupler or buttfusion/electrofusion techniques. The couplers on the inside ace as a bell and spigot type of joint.

 

[jgailla]

I'm still not getting it. Have you tried ADS? They have corrugated pipe which normally are installed similar to a bell and spigot and they also have couplings for corrugated pipe.
Corrugated HDPE is widely used for stormwater applications (although I don't recommend it) and you shouldn't need an internal coupling.

 

[dicksewerrat]

Are you using these internal coonectors for all your lines? Why are you using corrugated pipe? I wouldn't use that stuff for sanitary sewers at all. Solid wall HDPE or bell and spigot PVC. if this pipe is aldready in place and leaking, I'd put a CIPP liner in it.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com