In article ,
Fred writes:
On Wed, 22 Aug 2012 11:49:36 +0100 (BST), "Dave Liquorice"
wrote:

You could just open the tap. But some Bib taps have a built in double
check valve this could be to drain the bit between the two valves.

This is what I believe it to be: to drain the non return valve.

It's also to check that both sides of the double check valve
are working (like you do;-). Without access between the two
valves, you can't test they both still work.

I think it is preferable to use a tap without a valve and install a
check valve inside the house to minimise the chances of it freezing?

That is the requirement nowadays - the double check valve must
be indoors, as they are otherwise silently destroyed by the first
frost.

At least, that's what I have done. The taps without an integral check
valve (ime, ymmv, etc) do not have this drain nut.

Fitted one for my brother a couple of weeks ago, and used a
separate double check valve on the indoor pipework. The
brass casting for the tap had a bulge where the access nut
would be, but it wasn't machined out.

The ones on double check valves usually have fibre washers
IME. Not seen one with an O-ring like the OP's.

--
Andrew Gabriel
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