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

[Jayp07]

Hi all,
The short version of my question is: Where in a 4 story vertical stack would a blockage have to be for sewage gases to come back out of a sink on the 4th floor?

See below: The Durgo valve is brand new but bad smells are coming out of the kitchen sink (1m away) and the cavity wall itself The Durgo valve is at the top of the stack and finished mid wall on the forth floor in the kitchen close to the sink.

The stack starts in the basement and comes straight up to the forth floor. The stack is used for grey water for all floors below it.

The sink trap has been cleaned out. I think a build up of pressure is sucking water out of the trap.

Please excuse the bad drawing. Any help would be much appreciated - Thank you!

Jason

 

[Ben-gee]

Vent the stack to outside .

 

[Jayp07]

Vent the stack to outside .

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?

 

[Jayp07]

Vent the stack to outside .

Also, if the stack is working properly - blockage free, there shouldn't be a need for a roof vent pipe. The Durgo/AA valve is designed to replace a roof vent?

 

[ShaunCorbs]

Also, if the stack is working properly - blockage free, there shouldn't be a need for a roof vent pipe. The Durgo/AA valve is designed to replace a roof vent?

Only if there’s another permanent vent on the drainage system

 

[Basher]

Also, if the stack is working properly - blockage free, there shouldn't be a need for a roof vent pipe. The Durgo/AA valve is designed to replace a roof vent?

An Air Admittance valve by definition doesn't let positive pressure out of the system, whereas an open roof vent does. So a positive pressure may cause sewer gases to blow past a trap, but if the vent pipe was open that wouldn't happen.
Building regs require an open vent somewhere on the system, although that might be on another stack or a neighbours house for example.
Sorry beaten to it by Shaun!

 

[Jayp07]

Only if there’s another permanent vent on the drainage system

Hey Shaun, Thank you for your reply. I don't think this stacks connects to any other open stack on the way way down. When you guys talk about 'the system' is that determined by the final connection at the bottom, whether that be a tank or sewage plant room. In which case, if another svp stack connected to that tank at the bottom ran parallel to the Durgo svp, that would be considered the 'open vent stack' for the pressure release?

Can I just add that in suspicion of a faulty durgo valve causing the problem, this was changed back in May to the one you see in the picture.

Given that the problem still exists - that suggests to me that neither valve was faulty and the problem is lower down in the system?

 

[Jayp07]

An Air Admittance valve by definition doesn't let positive pressure out of the system, whereas an open roof vent does. So a positive pressure may cause sewer gases to blow past a trap, but if the vent pipe was open that wouldn't happen.
Building regs require an open vent somewhere on the system, although that might be on another stack or a neighbours house for example.
Sorry beaten to it by Shaun!

Thanks for taking the time to reply Basher, much appreciated. Okay so going by what you have said if there was no access to the roof vent pipe lower down for whatever reason, the durgo stack is now left with a build up of positive pressure, which could be whats coming out of the sink. Is that right?

But then why does the positive pressure come back up to the top of the stack on the 4th floor and not find an easier path of no resistance on the way up?

 

[ShaunCorbs]

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

 

[Basher]

But then why does the positive pressure come back up to the top of the stack on the 4th floor and not find an easier path of no resistance on the way up?

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

 

[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