Bar Screen in Sewer Manhole 2

[Carter05]

We are working with a sewage district that REQUIRES bar screens in sewer manholes under certain circumstances. Primarily, they require bar screens in the uphill manhole just before any steep section of gravity sewer. This seems like a very bad idea, with a lot of headaches for the system operators. We have not even been able to get a response as to why they want this item.....it is just required, period. Does anyone else out there know of districts requiring such a feature (disaster!) and why? Even better, can anyone link me to some logic or codes that address this issue?
Thanks

 

[SteveWag]

I’ve never seen a requirement like that, but there are lots of things I’ve never seen. If confronted with a requirement like that I would ask for a design standard, or at least a drawing (field trip?) of an installation, in their system that they are satisfied with. Did they specify bar spacing? If they are a client, or if your client is in their jurisdiction, I would not argue with them, just find out what they want.
Steve

 

[bimr]

Would agree with SteveWag, why argue if this is something that they truly want and have installed before.

I do think that it would be prudent to point out that the sewer is considered a confined space and for that reason, it would be very difficult and expensive to service such an installation.

 

[Carter05]

To SteveWag and bimr:
Thanks for the suggestions. I should have stated that the district is the reviewing agency, our client is a major developer, and wants to operate and maintain the water and sewer systems themselves (having many such systems around the country). Therefore, while in general I agree with the suggestion that we just comply with the reviewing agencys requirements, (and having been part of such agencies myself in the past), I do not want to create a headache for our client, and a possibly dangerous situation for the client's operators. If I could get the reviewing agency to simply state why they want bar screens in manholes, I might be able to logically understand, or conversely, to explain better the logic against them. However, I am faced with a "do this because we say so" stance that I find very hard to deal with. Thanks, and any additional comments would be appreciated.

 

[RWF7437]

If you can't convince them ( the reviewing agency) and they will not be operating the system once it is completed install the screens, hinged at the top for easy cleaning and removal. Then, if they prove to be a headache, swing them up out of the way or remove them. ( they MUST be removable in an emergency to prevent overflows). Document the maintenance headaches created by these screens over a trial period , say 6 months. Then decide whether or not to keep them in place. Unless these screens do something to protect downstream users and unless there isn't a better way to protect those users you will almost certainly be better off without them.

good luck

 

[nbuc7]

How are they planning on cleaning screens installed in a manhole??? Under extreme events when high peak flows are experienced, blinding of screens in the collection system sounds like a recipe for trouble.

 

[jartgo]

I just completed a design for one under similar circumstances. I ended up fabricating the the screen from stainless rebar so that it will slide into rails attached to the walls of the existing downstream manhole. Having the concerns that nbuc7 pointed out above, I also installed float switch with audio/visual alarm in the manhole so that when it did clog up (and it will), maintenance folks (at the facility I was permitting) would be made aware of the issue. In my case, the facility was responsible for maintenance of the screen and I made it clear to them that the screen should be checked daily.

We had the option of either installing a muffin monster or a bar screen, the client preferred the screen. It's not a perfect design, but it satisfied all those involved.