Velocity Dissipater Manhole

[btwhite01]

I'm designing a section of gravity sewer with a section of steep slope that falls into a very flat slope. (before manhole the slope is 9.4% and after 0.4%) My concern is with corrosion in the manhole and other possible issues with the high velocities. I've heard mention of some type of dissipator within a manhole. Is anyone familiar with anything such as this or have any ideas similiar in nature.

Thanks!
Brian

 

[dicksewerrat]

If you are using plastic pipe, you can start deflecting the joints to flatten the slope. If not then you will have corrosion in the structure that you change grade. You will also have an odor problem. another way to slow down the flow is to upsize the pipe a few times.
Put in one size up for two pipe lengths and then another upsize before the structure. I just had a brain cramp. Put a structure 6-8 pipe lengths upstream from the grade break and another 3-5 pipe lengths down stream.Use this point to start your grade change, by deflecting joints. The pipe may get shallow but that can be taken care of. If you can get 1 degree less pitch for each pipe, you should be able to eliminate a lot of odor. And odor is just a sign that H2S is coming out of solution in the effluent.

 

[upwey]

Pressure and odour issues are not uncommon. Purpose built covers and frames are now available with corrosion being offset with T316 parts and NBR gaskets.

http://www.upwey.com

 

[rak74]

Ran into a similar situation where we used a thick epoxy to coat the inside of the manhole to avoid corrosion. Deflecting push-on joints for gravity sewers on steep slopes can be dangerous and increases the potential for I&I. May want to look at HDPE pipe.