Plumbers : What is a Air Admittance Valve?

BDEE

BDEE

BDEE

Soldato
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21 Apr 2011
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So I have been ripping out some plumbing and come across something boxed in, in what was my downstairs toilet room.

I have found a tall pipe coming off a join where the soil pipe from the old toilet runs into the ground.

It is a tall pipe, maybe 3 ft high, capped with a "S450 Air Admittance Valve 110MM" made by Hunter plastics.

Link here : http://www.hunterplastics.co.uk/media/3128/ws450.jpg?height=800 to what it looks like.

I have a couple of questions.

1. What purpose does it serve? It appears to have an air tight seal so not sure how it admits air. Also why is it needed, as surely the waste just runs down the soil pipe and away?

2. I no longer have the toilet in situ and the soil pipe has been capped at the old join from the toilet. There is a working sink which is still attached to the same soil pipe. Is it OK to remove the pipe with this valve and cap where it joins the main soil pipe, so that I just have the sink feeding into the main soil pipe and then two joins capped off, and are there any implications of me doing this?

3. If I ever re-instate the toilet, will I need to re-instate this pipe and what would be the consequence of not doing so?


Thanks in advance!
 
I Thought that rexs link explained it very clearly:confused:
What are you still unclear about?

To sum it up yes you should still have a durgo installed
 
Is there any other route for air to be drawn into the system? If you don't have either a stack vent or an air admittance valve then when you flush the loo it sucks all the water out of your wate traps and lets the smell of the drains back in.
 
Start things off with the traditional "I'm not a plumber" disclaimer! This is just my understanding from doing work on my house... I believe that an air admittance valve replaces old breather caps on soil pipes above the roof line. The reason for this is that when a toilet is flushed, the water going down the soil pipe could create a seal and the resulting vacuum will pull the water out of your traps in your sinks etc. meaning that you will have a direct air connection to the sewer.

So:

1) As above, the valve itself is a one way value and will only allow air in (hence air admittance) so preventing the vacuums from occurring. I think it is the pressure from the vacuum that causes the internal valve to open and bring in air, stopping the traps from being emptied.
2) It depends on if there are any other routes for air to get in, if everything has a trap and is airtight, then you could potentially get a vacuum forming and therefore air will be drawn into the system from any available routes (through any sinks, toilets etc) connected to the same soil stack. Do you have any other toilets attached to the same run of soil?
3) As per the first paragraph...

This might all be rubbish but it is my understanding of it all! Hopefully someone with real knowledge will be able to contribute too!
 
OK, so there are two other toilets in the house - I cant see any other soil pipes going into this one though.

There is the one sink still attached, so the only airflow, if this is a soil pipe solely for this toilet room, then the only remaning air intake would be from the sink. But would it need any more intake than that? This is what I am trying to understand. As stated, there is no longer a toilet attached to where this pipe is.

So if I remove it and I flushed another toilet in the house, if that fed into this soil pipe, then I am going to end up with gases from the soil pipe coming back into the house?

If the other toilets flush into different pipes, is there any reason that it cannot be removed?

*edit*
Had a look and the main bathroom toilet has a valve in the wall void behind it with a vent. I believe also there is one in the loft which goes to the en-suite - need to double check it is the same valve but there is something there which looks the same and always wondered what it was for... so the question would still stand - is it needed for just a sink feeding into the soil pipe as it appears the other toilets have their own
 
Last edited:
BDEE said:
OK, so there are two other toilets in the house - I cant see any other soil pipes going into this one though.

There is the one sink still attached, so the only airflow, if this is a soil pipe solely for this toilet room, then the only remaning air intake would be from the sink. But would it need any more intake than that? This is what I am trying to understand. As stated, there is no longer a toilet attached to where this pipe is.
Click to expand...

The sink being attached does not give it any airflow in, it will (almost definitely) have a u-bend giving it a trap prevent air coming up from the sewer
 
Poolybit said:
The sink being attached does not give it any airflow in, it will (almost definitely) have a u-bend giving it a trap prevent air coming up from the sewer
Click to expand...

It does indeed. I assume though that with there being nothing else apparently attached that say, the toilet flushing upstairs, isn't going to then flush out the trap on that sink?
 
The general rule of thumb is that your 100 mm pipe you'll need to have a vent point within 6m of your sanitary fitments. You can, as in this case, fit a stub stack with the durgo valve aka air admittance valve to do a similar job but without venting to the external air.
With the toilet removed you could remove the stub stack however you would need to fit one to the sink as the pipe from that 40mm has a limit of 2m length without being vented.
Probably be best to keep it in place for ease of reinstating the toilet later.
 
Great thanks - That gives me what I need to know. I will box it back in and leave where it is, as would not be able to fit one in anywhere else for the sink.
 
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