Dergo valves , ventilation, and BCOs

[Lobster]

Hi I've just installed an bathroom, using a newly-installed internal soil stack, with a dergo valve to ventilate the soil stack, located in the bathroom next to the loo/bath, behind an access panel (as directed by the groundwork company who recently fitted the new soil pipe for me).

The BCO came to sign this off yesterday - unfortunately I wasn't there, but he said it was currently inadequate. Because I'd used a Dergo valve I apparently need to install a separate vent pipe (can be narrower than a 4" soil pipe) up through the roof, open to the air. This has confused me because why do I need both an open pipe as well as a Dergo? He's expecting the Dergo still to be there when I've finished; why? If the soil stack is open to the air, then what's the Dergo for?

In due course I'm fitting another bathroom, which will share the same soil stack (ie with two toilets) - which is on the BC application too

- does that have anything to do with it?

Obviously I need to go back to the BCO and find out exactly what I need to do (and it doesn't sound too drastic); but I'd just like to know what I'm talking about first!

Thanks David

[IMM]

You require an open vent stack at the 4th or 5th house, the end of run, like end of a cul-de-sec. Find out from the council, before you do what he says. If he is making you do something that is unnecessary show he the regs. Some BCOs are way behind in some fields.

Check out

and go to HepVO. Use these traps on all appliances and all is fine: no open stack needed. Hepworth will help you with the regs and give you details to give to the BCO.

[Lobster]

Thanks - yes sounds the same info I got from the groundwork guys, as being the reason why we didn't need an open vent: because it's a mid-terrace and the houses on both sides have open soil stacks. SWMBO pointed this out to the BCO when he inspected, but he said we still needed an open vent in our property. Sounds iffy to me!

Will play this one by ear I think; sounds like a relatively trivial alteration and I really don't want to piss the guy off by second-guessing him, as I really need to stay on good terms with him for what's coming next (readers may remember my posts of a few weeks back asking about running the soil from house A into the internal soil stack of house B!)

David

[River Tramp]

I must admit I have fallen into requiring each property had a natural vented SVP, when really it should be every 4th property and head of run (but won't in future).

However I always insist on an air test on the new plumbing with the AAV/Durgo in position, as we have found they do leak (foul) air out.

RT

[The Natural Philosopher]

Dergos and vents serve two different purposes. The durgo is there to stop suction emptying nearby traps. The stack is there to vent off poitive pressure noxious gasses.

The posituve pressure vent need not be fast acting, and so is allowed to be I think as small as 2" diameter. The negative pressure stuff needs to act fast in a flush, and so is normally full bore to the vent or durgo.

[IMM]

HepVo traps are the better option, dispensing with Durgos (air admittance valve) and their bulk.

[Hugo Nebula]

On 13 Feb 2004 05:36:13 -0800, a particular chimpanzee named [e-mail] (Lobster) randomly hit the keyboard and produced:

An air-admittance valve ("Durgo" is a trade name) can be used in lieu of an open stack for a single house, if the drain connects to a vented common drain or sewer.

The BBA certificate for Durgo says, "To contribute to the ventilation of the underground drain and to minimise the effects of excessive back pressures when a drain blockage occurs, the branch or main drain serving a stack or stacks fitted with Durgo valves may require venting at a point upstream of the stack connection. For guidance the following should be noted (see Figure 5): (a) For up to and including four dwellings, 1, 2, or 3 storeys in height, additional drain venting is not required. Where a drain serves more than four such dwellings equipped with the valve, the drain should be vented according to the following rule, either by a conventional open-topped ventilating stack or discharge stack:

5 to 10 such dwellings ? conventional ventilation to be provided at the head of the system 11 to 20 such dwellings ? conventional ventilation to be provided at the mid-point and at the head of the system". (BBA Certificate 97/3427

[The Natural Philosopher]

Point of information. A rond tuit came home to roost this week, adn yes, not 2 bathroom was deemed to be teh target of 'when are you going to sort that out' ....

To cut a long story short, the loo came out completely,, and had a lastic bag taped over the soil stack to keep the pongs down.

Every time i empty the bath (this on a vented stack by the way) the bag first bulges out under positive pressure, then gets sucked in by negative pressure. Quite a bit in both cases. I weould point out that te stack this is all conneceted too has a 3" pipe about 10m long venting down the back of the house, and the bath waste joins it below the loo pipe.

The basin trap - coupled to the bath waste - gurgles as well.

I was surprised at the pressure changes. With a durgo, there might well be enough local pressure build up to pop the odd trap.

Vent your stacks guys. Even if teh regs say you don't need to.

[Andy Hall]

Is it generic or is it just me that when you eventually get started on such a tuit, that about half an hour into it, another tuit becomes more important and one gets diverted onto that?

.andy

To email, substitute .nospam with .gl

[The Natural Philosopher]

Generic. shes now started gazing at 'net pictures of giant baths with a huge price tag for the 4th bathroom. The BIG ONE.