John P
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| posted on 1/8/14 at 02:54 PM |
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Why do I get air bubbling up from the sink?
I've been trying to understand this for some time but ever since we moved into our bungalow there have been gurgling noises every time water
runs down the sink and occasionally a smell of drains.
Today I tried to sort out what’s actually happening so I blocked up the overflow and filled both bowls with water (it’s a 1 and ½ bowl sink). If I
let the water escape from either bowl then, remembering I had blocked the overflow, there is a noticeable volume of air which bubbles up from the
other bowl.
It’s almost as though air can’t escape down the waste (which runs to an open gulley) so for the water to go down it has to displace the air in the
waste pipe which then bubbles up through the sink.
The only doubtful thing about the existing installation is that there is no trap under the sink and that the total run from the sink to the open
gulley is around 8 metres.
It would be very difficult at present to fit a trap without taking out the entire sink unit and as I will be replacing the kitchen in a few months I
would like to try to come up with a short term fix until then. If a trap would definitely sort the problem then that's what I'll have to
do but at the moment I'm not convinced it will help even though it obviously should be there.
I did post this query a few weeks ago and it was suggested I fit an air admittance valve but I can’t see how this would help as the problem seems to
be air which is unable to escape rather than being drawn in.
Any suggestions?
John.
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minitici
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| posted on 1/8/14 at 03:55 PM |
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You should have some form of trap on your sink and the waste line should have an air vent pipe on the downstream side of the trap.
An 8 metre run of pipe without a vent will cause problems.
As has been suggested an automatic air admittance valve can be fitted to the waste line in place of a vent stack. (Normally you will still need a vent
stack somewhere in the waste pipe run - usually at the furthest sink/bath/etc)
[Edited on 1/8/14 by minitici]
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ian locostzx9rc2
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| posted on 1/8/14 at 05:16 PM |
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You need some sort of u bend trap in the system that should sort the problems out.
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Smokey mow
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| posted on 1/8/14 at 05:21 PM |
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quote:
Originally posted by John P
The only doubtful thing about the existing installation is that there is no trap under the sink and that the total run from the sink to the open
gulley is around 8 metres.
the maximum length of a sink waste should be 3m for a 40mm diameter pipe and 4m max if 50mm diameter. At 8m long you'll almost
certainly suffer from syphonage of the waste as it trys to pull a plug of air through behind the water. Ideally you should be venting the waste to
prevent it from happening whist also fitting a trap to stop the smells comming up from the drain but it doesn't sound like that's
practical.
You could alternatively fit a dry inline trap such as the HepVo http://www.hepvo.com/
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John P
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| posted on 1/8/14 at 05:55 PM |
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Smokey mow
I understand what your saying and if I had a trap from which the water was being syphoned out I'd understand the need to provide some form of
vent but why would the air be bubbling back up into the sink?
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Smokey mow
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| posted on 1/8/14 at 07:25 PM |
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The air in the pipe has to both come and go from somewhere. The easiest place for it to do this is via the other sink.
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JoelP
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| posted on 1/8/14 at 07:47 PM |
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The trap stops smells coming out. The air vent stops the long run sucking the water out of the trap.
I would suggest that your existing long pipe has sagged somewhere making a makeshift trap, this would explain why it doesn't normally smell and
the bubbling too.
Beware! Bourettes is binfectious.
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John P
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| posted on 14/8/14 at 05:43 PM |
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Just wanted to thank everyone for their advice.
Although I still didn't really understand exactly why I was doing it, earlier today I managed to get into the void below the floor and found
there was a very shallow trap in the waste pipe.
I replaced this with a much deeper version and added an air-admittance valve as suggested.
When we ran some water out of the sink I was amazed to hear the air-admittance valve obviously opening and now there's no bubbling and no
smells!
I'm well pleased with that and it actually only took about an hour to do.
John.
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