Locking lid for Osma inspection chamber?

[cjcoffin]

Because we live at the bottom of the hill and our neighbours have already been flooded with sewage from a blocked public sewer, I plan to install a non-return valve in the foul drain from our house.

The NRV will have to go upstream of the last manhole on our property as this is right up against the boundary, so I would like to fit it with a lockable cover to prevent it being lifted by sewage backing up from the main sewer.

The inspection chamber is 450mm diameter and has a ductile iron Osma lid and frame set in a tarmac driveway. Obviously I would like to avoid digging it all out and replacing it completely. Is there a good way of getting round this?

TIA

 

[Hugh Jaleak]

I'm not aware of a lockable lid that will fit directly into the existing frame, to achieve your aim I think you would be looking at the internal covers with a screwed down cover. These (AFAIK) are only available in rectangular covers.

Question of hydraulics springs to mind though, you cannot compress a fluid. If the sewers were to block again, and you are attempting to block the natural path of the water to escape, it could blow any cover (possibly complete with the frame) out of the ground! The 'Class A' ductile iron covers (as found in the road) are bl00dy heavy, and require a 2 person lift, yet water under pressure from below can lift these covers clean out the frame. (I have even known the cover and frame (and quite a few paviours) to be blown out of a block paved roadway!)

If the manhole just inside your boundary is the lowest point, should worst happen then the backed up effluent would escape from that point anyway. Making attempts to prevent that may just move the escape route elsewhere!

 

[cjcoffin]

If the manhole just inside your boundary is the lowest point, should worst happen then the backed up effluent would escape from that point anyway. Making attempts to prevent that may just move the escape route elsewhere!

No, its more complicated than that. This manhole is (naturally) at the lowest point of my drain, but the ground rises towards the road so the drain is five feet down at that point. Hence I can't put the NRV there as it would be too far down to access it for inspection and cleaning.

Also if anything lifts the lid the resulting effluent will run down the drive towards the house and the surface water drains are not adequate to cope with the anticipated flow. We have enough trouble with rainwater running off the road without that.

What I want to achieve is indeed to move the potential escape route elsewhere - and make sure it is not on my property. If it lifts a cover in the road then SWW will have to come and sort it but it is unlikely to flood my house!

 

[Hugh Jaleak]

Only 5 feet down? Thats shallow, try 5 metres down!

Possible Clark-Drain may have something akin to what you require, http://www.clark-drain.com/ but as to whether it will hold the pressure should the drain back up is probably down to how securely you can fit it (and seal it) onto the chamber in question.....