Durgo not fully working

[Minky]

Hi all,

 

I've recently had a wetroom installed and at the time it wasn't possible to connect the waste pipe of this onto the existing soil stack which vents out the roof. So it drains via a separate waste pipe which eventually joins the overall drains under the house.

 

Pretty soon we realised that we needed an Air Admittance valve as the shower was very slow to drain. This has now been fitted, however it hasn't resulted in the quick draining of the shower as I had hoped.

 

So am looking for advice on what the problem is here.

 

Removing the durgo (and leaving the pipe open at the top) enables the water to drain super quick, but when the durgo is back on the shower is slow to drain again. It's like maybe the durgo isn't powerful enough (do these come in ranges?) or the pressure produced by the shower draining isn't enough to push the air back up into the durgo and take the air that it needs? 

 

I've attached a photo of the pipe work installed for the shower waste and the durgo. The long white pipe to the left is the shower waste pipe, just above the ceiling it goes directly to join the shower trap. The pipe snaking off to the right is the one put in for the durgo. It goes through the ceiling into the bedroom next to the wetroom (there wasn't anywhere to put it in the bedroom) and ends about a foot above the bedroom floor.

 

Would appreciate any suggestions as this is driving me mad!

[ProDave]

The Durgo is supposed to go on the top if the pipe the water flows down so the slug of water creates a vacuum and the Durgo allows air to enter to replace that.  Having the Durgo off on a separate branch is not going to help that at all.  You need to continue the shower waste pipe past the shower trap then up somehwere and that is where the Durgo goes.

[Minky]

Thanks ProDave, are you saying that the Durgo needs to branch off higher than it currently is? Literally above the plasterboard you can see, is the shower trap so the Durgo couldn't go any higher on here, but maybe if the branch off for the Durgo happened here and then across to where it goes up into the ceiling - would that make it work?

[ProDave]

I can't picture what is happening above the ceiling, but the Durgo should be above where the water enters the pipe runs, so usually instead of an elbow at the shower trap, have a tee, and continue the pipe a bit further and fit the durgo to that.

[Minky]

That's the challenge, pretty much from the hole in the ceiling on the left to the hole on the right is tiled floor (the wetroom floor), there is no where for a durgo to go up into the floor next to the shower trap.

 

Potentially the tee off to the durgo could be fitted higher, maybe 8 inches or so, but it will still need to run across to the right and go up at that position. But I am reluctant to do this rework unless it's definitely going to solve the problem!

[Mr Punter]

As it works without the durgo, have you looked at swapping it for another brand?  Try a https://www.screwfix.com/p/floplast-af32w-air-admittance-valve/42968 and just take it back if it doesn't work out.

[Minky]

Actually yes, as soon as we realised the first valve wasn't really having any effect we went to screwfix and got a McAlpine Ventapipe. Unfortunately we couldn't connect it to the pipe as it was a smaller diameter but just to try it we gaffer taped it on and there was a slight improvement - even though still not like without any durgo on.

So that's why I was wondering, are there different "strengths" of durgo? This one you suggested, I can see it's had quite good reviews - have you used it before?

[Carrerahill]

5 minutes ago, Minky said:

Actually yes, as soon as we realised the first valve wasn't really having any effect we went to screwfix and got a McAlpine Ventapipe. Unfortunately we couldn't connect it to the pipe as it was a smaller diameter but just to try it we gaffer taped it on and there was a slight improvement - even though still not like without any durgo on.

So that's why I was wondering, are there different "strengths" of durgo? This one you suggested, I can see it's had quite good reviews - have you used it before?

Could you remove that plasterboard, and install a T just after the shower tray, then run a pipe to a higher location?

 

As for differing AAV air volumes, not really, a very small opening will allow a lot of air to pass, if it was undersized, i.e. a 40mm AAV on a soil stack it would just make a air woosh/whistle noise and it would not be correct, but an AAV for a given size of pipework will be adequate to drain that size.

 

I suspect that your issue is that the placement is not correct and that the vacuum with the AAV installed is not great enough to pull the diaphragm down and thus let air enter - with it removed you said it drains a treat, which means that the system is wanting air but the placement is wrong. Judging by the location of the boiler I assume the LHS is an external wall? Could you T off under the shower tray and run a pipe to the outside of the building and deal with it there?

[CC45]

I assume the straight vertical drop from the shower doesn't help - if it run horizontally towards the durgo and then went straight down (and then back over) - would that allow the durgo air to enter the system where the water drops vertically?

[Minky]

Thanks Carrerahill, can't really take the pipe out the side of the house as it's already up to the boundary of the neighbour.

 

It is possible to remove the plasterboard and fit the T piece higher up though, but it would still need to run across to the left and then up that hole that's been cut out - to the right of that is the wetroom floor which is all tiled and it's just not an option to have the durgo coming up into that area.

 

CC45 - I did consider that, looking at how the pipe is currently if it was the durgo on the left and the shower trap on the right I am assuming there would be no issue here. But unfortunately this was all an afterthought when we discovered we couldnt join the shower waste onto the existing soil stack. Are you suggesting to have the durgo pipe extend down further and across to join the waste pipe and the shower waste to a t-piece onto here? I guess it's possible although it would look pretty messy, as it's the garage wall we could get away with it.

[CC45]

Perhaps run the shower waste at a shallow angle (1:40?) over towards where you've mounted the durgo - put an equal tee in there so the durgo sits directly on top of the vertical drop, then when its close to the floor take it back over to where the waste goes currently.  I guess you could even plumb 2 durgo's in if you wanted to - it would introduce more air into the system.  I'm not a plumber but I wonder if its the straight drop from the shower thats causing the issue. You could try all this out fairly easily and if it didn't work it wouldn't be the end of the world - a lot easier than drilling through walls etc.   

[jack]

Air admittance vales are at their best when you have a large slug of water draining all at once - think toilets, sinks (if draining from full) and baths.

 

In your case, you're draining something that will generate a steady but relatively small flow of water. It therefore won't build up a slug of water in the vertical pipe to which your durgo attaches. In that case, the only source of the vacuum is whatever happens below the vertical run shown in your pic. Because that's so far away from the durgo, the large volume of air in the circuit (all legs) between the durgo and the bottom of the pipe may be preventing an effective vacuum from forming. Whatever low vacuum is building may be enough to slow drainage but not enough to allow the durgo to open properly.

 

The vacuum may also be intermittent if whatever's causing it down below isn't continuous (eg, if it periodically allows air to burp up from further down the pipework), which will again prevent the durgo from operating correctly.

 

If any or all of this is true, putting a trap directly below the "T" to the durgo might help, and isn't too expensive or disruptive an option to test.

 

Optionally, you might put an elbow on the left hand pipework to take it over to underneath the durgo pipework, then put a trap below with vertical up to the durgo, and then another elbow back to the existing vertical pipe (or maybe vertically down to wall, then across to the left lower down, if that isn't in the way). That would drastically reduce the volume of air in the circuit within which the durgo is operating.

 

Please note that all of this might well be nonsense, as it's just based on me thinking about how all this might work, rather than having any real knowledge of how it does work!

[Minky]

Thanks Jack, if I understand correctly you're suggesting moving the shower trap to below where the waste pipe forks off to the durgo - as that might increase the force of the shower water entering the pipe? The problem is that this is a wet room so the shower trap is "built-in" to the floor. But I agree that maybe the force of the water moving through this isn't enough to force the air across to the durgo.

 

CC45 - I see what you're saying here and it might be easy enough to try. It would be annoying having a soil pipe in the middle of the garage but probably not as annoying as a slow draining shower!

[CC45]

if what I suggest works then it might be worth returning the pipe up higher up the wall if having it in the middle of the garage annoys you - bit of zig zag pipe work but if it works you could always box it in.

[jack]

31 minutes ago, Minky said:

Thanks Jack, if I understand correctly you're suggesting moving the shower trap to below where the waste pipe forks off to the durgo - as that might increase the force of the shower water entering the pipe?

 

Not quite - I was suggesting putting another trap at that location and leaving the shower as it is. 

 

Picture's worth a thousand words and all that:

 

[Minky]

Thanks Jack, and excuse my ignorance but how would putting another trap below the durgo help the pressure? (without being too technical if that is possible).

 

CC45 - that would be an option, thanks for that.

[Nickfromwales]

 

Thats on my current wetroom job. 

Right hand 50mm goes to the free standing bath and basin as shown below. 

 

 

The first pic shows the 50mm tee ( for the shower ) with a 32mm branch going off to the new airing cupboard. In there will be a short section of 32mm pipe, a 32mm tee, a 32mm AAV in the top of the tee, and then the boiler condensate into the same tee on a 32x21.5mm reducer. 

The pipe going down the wall should have been 50mm TBH, as you then get a massive improvement on air break. It'll basically be almost trying to form a syphon as it falls vertically so not the best bit of plumbing TBH. The rule is when dropping like that to oversize to get an air break. Yes, an AAV will allow air in, but not at the tornado rates that you'll be needing. 

Edited August 8, 2018 by Nickfromwales
Edited because Apple won't let me spell the bastard word syphon ffs.

[jack]

The problem with all of this is that these are complex systems. It may be that there's some sort of dynamic restriction somewhere further down the pipework that's actually getting the benefit of the air when it's allowed in. One problem is that any such restriction is far from where the air is being admitted, and there's a lot of air volume to reduce in pressure to get the durgo to open.

 

You also have a relatively low water flow (compared to something like a draining sink or bath) relative to the size of the waste pipe, so it likely won't cause much pressure reduction due to air entrainment (moving water drags some air along with it = reduced pressure upstream due to removed air).

 

I initially thought that putting a trap below the durgo would mean that the volume on the pipe side of the durgo is much reduced. That assists one side of the equation. The main impact would be to decouple the waste above from the part below the durgo, with a corresponding reduction in air volume, but as I think harder, I wonder whether the impact of slowing the water at this point due to the trap might make this somewhat self-defeating .

 

As @CC45 mentioned, it might also be worth dropping vertically from below the durgo then back across to the existing waste lower down. That will give you more water velocity nearer the durgo, and hence greater pressure reduction to help the durgo open. 

 

As above though, these are complex systems. Given the fact that I'm just thinking out loud, it's probably best to ignore everything I'm saying and listen to those who have a better idea of these things in practice!

 

[CC45]

does the shower waste enter a 110mm pipe at the garage floor?

[jack]

5 minutes ago, Nickfromwales said:

The pipe going down the wall should have been 50mm TBH, as you then get a massive improvement on air break. It'll basically be almost trying to form a stohon as it falls vertically so not the best bit of pushing TBH. The rule is when dropping like that to oversize to get an air break. Yes, an AAV will allow air in, but not at the tornado rates that you'll be needing. 

 

Can you please explain this a bit more Nick? You say to go 50mm (which I think is smaller than what's in the first picture), but then say to "oversize" to get an air break.

 

Also, is "stohon" Welsh for something? 

 

2 minutes ago, CC45 said:

does the shower waste enter a 110mm pipe at the garage floor?

 

Doesn't look like it:

 

5 hours ago, Minky said:

...  at the time it wasn't possible to connect the waste pipe of this onto the existing soil stack which vents out the roof. So it drains via a separate waste pipe which eventually joins the overall drains under the house.

[Minky]

CC45 - i cant remember the actual diameter of the pipe but from memory it is around 110mm. Not sure if it makes any difference but a sink trap (in the garage) also enters and empties into this pipe.

[CC45]

worth asking..... but well observed!

[Mr Punter]

4 minutes ago, jack said:

Also, is "stohon" Welsh for something?

 

Does it mean "covfefe"?

[Minky]

Just re: the garage floor pipe, this was newly put in and joins the main drainage pipe under the house. The existing soil stack separately empties into the main drainage pipe.

 

The reason why this garage floor pipe was put in was because we put in a sink in the garage and this was to drain into this garage floor pipe along with the washing machine (which empties into the sink trap pipework).

When we realised we couldn't run the shower trap to the existing soil stack it made sense to have it emptying into these new pipes we had.

[CC45]

Just now, Minky said:

CC45 - i cant remember the actual diameter of the pipe but from memory it is around 110mm. Not sure if it makes any difference but a sink trap (in the garage) also enters and empties into this pipe.

so if there's a 110mm pipe there - why can this be extended up the wall so the section between the shower trap and this pipe is minimal - I'm assuming the water from a shower would fall down a 110mm pipe without creating much of a vaccuum - I know this won't open the durga but if there's no vaccum created then it doesn't need to; there should be no reduction in flow - so your feet shouldn't be having a bath while the rest of you is having a shower.  Just wondering if a 110mm equal tee under the ceiling - leading off to a 110mm durga situated under the ceiling would work?  I know the durga should be above the shower waste but whats the chance of it being flooded out when its all attached to 110mm pipe.

 

Does the sink also have an aav on it? 

 

@Nickfromwales is the resident expert on here; I could be all wrong here!