On Sat, 04 Jun 2011 10:04:41 +0000, Andrew Gabriel wrote:

It's a regular failure of these valves. You can't leave them open all
the time, as the seal relies on being wet, which leaves an area which
will dry and form scale, and then no longer seal.

No, that's the fibre-washer type. Bottle type AAVs have a float which,
when it rises, closes a hole above it which (when there's air in the
system and the float isn't floating) lets the air out. It's the
suspension of the float mechanism that I referred to as dainty. These
types of AAV do usually have a sealing cap but these can usually be left
partially unscrewed to act as a dust cap whilst allowing air out.


--
John Stumbles -- http://yaph.co.uk

Thesaurus: extinct reptile noted for its wide vocabulary.