NRV in private sewer line.. experiences?

[Whitling2k]

Hi all

I'm thinking of installing an NRV in my houses main sewer line to avoid backflows from the street's main sewer during intense rainfall.

I know there are loads of pros/cons/pitfalls etc - and I'm getting a bit dizzy looking into all the options.

Does anyone have any practical experience of installing and/or living with one of these?

I like the idea of an open one (one of these in a new inspection chamber) so I can spray it, rod it etc to keep it maintained without getting down and dirty with bolts and lids etc. The head of water I'm dealing with would be OK with this setup.

However, most places only seem to sell/recommend these - which look like they have so much potential for going wrong - then being impossible to repair without hugging it to get access to the internals.

I also don't like the idea of those retrofit jobs - where you just slot them down the pipe - they look to reduce the capacity of the pipe and introduce too much of an obstacle. My overall sewage line gradient is very low.

Tia

Whitling2k

 

[bernardgreen]

Not personally but the cellar of a house in the village had several floods when the village pumping station couldn't cope.

Anglian Water fitted a non return valve to the pipe from the house at the chamber in the street. This has prevented the house being flooded on a couple of occasions when the pumping station failed to cope.

It may be that your water company would fit one for you if their sewer system was at fault.

 

[freddiemercurystwin]

For the uneducated here, if you fitted the first suggestion, in a new manhole, what's to stop the manhole filling up and overflowing? Or is that the idea - so the manhole floods rather than anything further upstream?

 

[Whitling2k]

@freddiemercurystwin - ground levels. Gradients work against me and dip the opposite direction to the drainage route.

My garden has the lowest ground levels in the street, the drains run about 8" below ground in my garden. It's about 3' deep in the street. From my garden towards the road, the ground level rises, then drops off again slightly in the street. My property boundary includes the high ground towards the road.

The water would spill elsewhere before it overtopped my new manhole. I would also specify a screw down lid. A five year old would describe it as so:

It may be that your water company would fit one for you if their sewer system was at fault.

This would be my jackpot. Annoyingly, the water company flat-out refuse to install one - saying if they build one, and it then causes flooding elsewhere, they may be held liable. But they 'don't think' I would be held liable if I built one - because it's 'not my sewage' that would be flooding out elsewhere. They would rather pay me ~£170 rebate each and every time if floods. It's happened so many times now that I can afford a few £k on my own NRV and not be out of pocket much.

I'm looking into
1. Will it actually do what I want
2. Will it become a maintenance nightmare, actually failing when I need it the most due to sediment and other objects in the way
3. What are the legal grounds for me doing it - can I be held liable for other's flooding if I don't let the system use my property as it's emergency overflow.

 

[bernardgreen]

Your situation is exactly the same as the house here/

What is the connection here

If it is a buried saddle connection then a new manhole may be the easiest option.

But if it is an inspection chamber large enough for a person to be lowered in to fit the NVR to your pipe then that is the way it should be achieved. ( as it was to the house here ).

Obviously the water board will prefer to take the easiest route but they also have a legal obligation to prevent sewage from their sewer polluting private property.

 

[HERTS P&D]

Bernad, your picture looks like a sex education picture for children.



Andy

 

[bernardgreen]

 

[Whitling2k]

it does!!

The connection to the rest of the sewer is a standard outfall, several house's branches come into a 90deg bend into a pipe of about 12" dia in the chamber in the street.

Unfortunately, a there is a lateral inflow from a highway gulley (not shown on my diagram) between my property and the outfall into the main chamber. If someone put an NRV at the outfall - during the storms, the inflow from the highway gulley would cause my sewer to flood anyway, and I'm no better off. Well, it would be cleaner water after the initial flush.

*But*, the neighbours also have their (mostly private branch) leading to a gully that also backs up when it rains a lot. They are oblivious, and in denial that it backs up - so the reality of putting the NRV at the end of my branch, is that the water would probably surcharge from my neighbours drain, run straight into the highway gulley, then back into my system - bypassing the terminal NRV. So would need their own NRV too, and the highway gulley diverting (or also NRVing). But no chance of that due to the aforementioned denial.

Also - they don't seem to think they have:

they also have a legal obligation to prevent sewage from their sewer polluting private property

They are scared of installing an NRV in case it causes flooding to someone else - and because it's one of their assets explicitly causing said flooding - they would be liable for any new flooding that didn't occur beforehand. But they are happy for me to be continuously flooded because it just happens. It's not explicitly caused by an intervention.

Part of the problem is that ground levels for the entire street go against the gradient of the sewer. There is almost no fall, but it's ~15 foot deep by the end of the street. My property is like a nested microcosm of the wider system.

 

[jeds]

Only ever specified one, which is a bit odd since nearly every planning app I do seems to need a flood risk assessment. I remember it was Forgevalve unit and looked more or less like a standard round access cover. You could open the cover and hose it out. I still do a lot of work for the owner. As far as I know he's never had an issue with it. In fact I doubt he even knows it exists.

 

[Hugh Jaleak]

Bear in mind, for installation and maintenance purposes, given the depth of the installation, you, (or whoever does the job going forward), will need Confined Space training, and the required safety kit, (harness, man riding winch, gas monitor, etc) to safely access the sewer.

I would also be careful, if your sewer has a very shallow fall on it, there is a concern if the flow is not at sufficient velocity to push past the NRV, it may cause more issues than it solves.

 

[Whitling2k]

Thankfully, it's not that deep. It will be about 3 foot deep, so an old fashioned brick build inspection chamber will allow inspection and installation. I'm not pressured for space either, and there are no electrical services near it. Just my incoming water main (which I want to re-lay too - but that's another story!)

I would also be careful, if your sewer has a very shallow fall on it, there is a concern if the flow is not at sufficient velocity to push past the NRV, it may cause more issues than it solves.

That is one of my concerns too. I'm trying to find some actual experience of them being fitted, which seems quite hard to come by.

My sewer essentially drains through the weight of the water behind it, rather than actively runs downhill (from what I can tell). It's horizontal to all intents and purposes. Which is another reason I want to be able to lift an inspection cover, then spray or rod for maintenance. Rather than having to get down and dirty, unbolt a sealed unit, let the dirty water spray out whilst the head equalises, then clean it.

The compact designs look great where space is a limiting factor - but space isn't limited in my install.

I'm also tempted just to install sealed manhole covers and drain covers - but my fear there, is I don't know how high the head of water is that it will be holding back - and if it's above the height of my downstairs toilet, that will then become the next lowest-point in the system. And an internal flood is a whole different ball game.