air admittance valve

9 May 2006
Reaction score
United Kingdom
I am running 6m of waste from en suite basin and shower, I have been advised to put air admittance valve near basin to avoid siphonage etc. What size in length and bore would this have to be ??, can it terminate in loft space directly above ??. It seems a 110mm air admittance valve used on soil stacks looks a bit full on, is there an interior domestic version??.
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I'd just use a vented trap.
Lots of patterns, eg

Bit of a misnomer cos they have aav's, not true vents, but would expect no problems. Pipe from basin should be 1½" if over 1.2m, and don't make it tee-in too near the shower or you'll get backflow into the shower just like the Costa Del Cheapo hotels. Best if pipe from shower drops a bit before the tee.

Can't remember the figure but I bet the book says the waste from the shower should be 50mm for 6m. Use a shower trap with a 50mm "seal" too. The 17mm seal ones suck out , and don't comply with any British building regulations though nearly everyone uses them.
Plumb Center do a small version for waste pipes........I use Hep V O waste valves instead.....but they cost over£10... and the adapters are extra....
Thanks chris n nige,
Have u had any experience with hep valves??, are they reliable??. Still thinking a vent up to the loft is a feasible solution. I suppose teed off waste terminating in an insect guard would do, as long as its above spill over level ?? Dunno, bit confused, dont want the 'home buyers' inspector telling me to rip it out when I move on in a couple of years.
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Hep valves :) just like a rubber tube inside lets water+air one way .Have used a few with excellent water seal to evaporate/blow back.Which anti vac traps can`t do
If you've just got a 6m branch off a vented stack pipe I don't think you'd need a vent for smells to get out of your branch.
Just one aav (on the basin trap) will allow air in at the tee point on the combined waste, so, it depens on the run length but I wouldn't expect a 50mm seal on the shower to be "pulled".

Have u had any experience with hep valves??,
What valve?
Their hepvo waste rubber trap things if you mean those, are good.

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