Durgo(AAV) Vertical Stack - Where would a blockage have to be?

[Ben-gee]

Thanks for the reply Ben-gee. Unfortunately, the stack is already in place and there is no chance of adding a vent to the roof. Any other ideas?

You’ve asked, most people are saying the same answer - you might not like it but that is your best bet (obviously none of us have seen it).

You say there is no chance of adding a roof vent - there will be, if May not be easy but it will be possible.

But don’t forget, you may be able to vent your drain system more easily elsewhere - get a local plumber to look at it for you.

 

[Jayp07]

Not being funny, but if I knew the reason for your issue I would have given a more helpful response in the first place!

Let's say this problem is not caused by a blockage within the stack:
The 'easiest path' will be the shallowest trap serving the stack.
It's not like a wave of water washing up the stack, wanting to come out of the lowest opening first.
Because of the 'low impedance' of the large diameter pipe, unless a very transient change in pressure, the air pressure will be the same throughout the stack, so it will leak through the easiest path. If you've got deeper traps on the lower floors, or a shallower or partly dried out trap at the top, the sewer gas will come out at the top.

On the other hand, if there is a blockage at the top of the stack between 3rd and 4th floors (I would imagine very unlikely), then the fumes could only get out at the top, and not through the Durgo!

Put a Hepvo trap on the sink and maybe another floor will get the fumes

My apologies Basher, I'm working my way through this and learning as I go. Your first answer was very helpful too. Thanks for taking the time to explain the impedance idea. My building is a new build block (5 years old) so in theory all of the traps on the way up should be the same spec and full of water. Presumably the fumes are getting to the top and emptying the sink trap.

I also think it is unlikely for there to be a block between 4th and 3rd.

Re the Hepvo valve - Ha! sounds like a good shout but my neighbours on the 3rd floor are pretty nice and they have a newborn, so I wouldn't want to pass this problem on to them

I'm going to see if I can get access to the pipe work plans of the building. I've got contractors coming in next week to cut access holes in walls to look for clues but I think they may have over looked the simpler answer (as discussed here). I just need to know what I'm talking about before taking them on.

 

[Jayp07]

Exactly so should of been vented externally from the start Durgos are only really good for let’s say flat 3 venting eg as if you flush yours it could pull a trap off the lower floors etc when the main vent eg yours with a Diego on now it’s venting to external

Thanks Shaun, you've guys have been a big help. So I really need to find out if there is a roof vent pipe supplying my durgo svp with air ? and then, is there a potential block in that pipe stopping getting to my stack, is that about right?

 

[Jayp07]

Sorry. one other question, why is it essential for a durgo stack to have a supporting roof vent stack? why not keep it under pressure and let it do its job to let air in when necessary to balance the pressure?

I've watched so much content on durgo valves over the last month but no one mentions a need to roof vent as well for a healthy system

 

[ShaunCorbs]

Thanks Shaun, you've guys have been a big help. So I really need to find out if there is a roof vent pipe supplying my durgo svp with air ? and then, is there a potential block in that pipe stopping getting to my stack, is that about right?

Yes but I very doubt it’s blocked as tbh there would be no waste on that pipe

 

[ShaunCorbs]

Sorry. one other question, why is it essential for a durgo stack to have a supporting roof vent stack? why not keep it under pressure and let it do its job to let air in when necessary to balance the pressure?

I've watched so much content on durgo valves over the last month but no one mentions a need to roof vent as well for a healthy system

It’s in building regs must have at least one open to atmosphere, it’s to do with pressure and there not suitable for venting whole drainage system mainly just to deal with pressure eg when you flush a toilet etc