I have just replaced a bib tap outside the house. I notice that both the
one that I took off and the new one have a small screw on the underside
of the tap near to where it connects to the supply.

Removing this screw reveals a small O ring around the screw and hole to
the water inlet.

But what is it for?

On Wed, 22 Aug 2012 11:11:25 +0100, Andrew May
wrote:

I have just replaced a bib tap outside the house. I notice that both the
one that I took off and the new one have a small screw on the underside
of the tap near to where it connects to the supply.

Removing this screw reveals a small O ring around the screw and hole to
the water inlet.

But what is it for?

Perhaps to drain the tap/pipe for cold spells.

--
Frank Erskine

On Wed, 22 Aug 2012 11:40:11 +0100, Frank Erskine wrote:

Removing this screw reveals a small O ring around the screw and hole
to the water inlet.

But what is it for?

Perhaps to drain the tap/pipe for cold spells.

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.

--
Cheers
Dave.

On 22/08/2012 11:49, Dave Liquorice wrote:
On Wed, 22 Aug 2012 11:40:11 +0100, Frank Erskine wrote:

Removing this screw reveals a small O ring around the screw and hole
to the water inlet.

But what is it for?

Perhaps to drain the tap/pipe for cold spells.

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.

That would make sense although I have a feeling that one did have a
non-return valve and the other did not.

It was the failure of the non-return bit that prompted its replacement.
A little O ring that seals it closed was coming loose and I was bu**ered
if I could find a way of getting it all apart to replace it.

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.

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

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
[email address is not usable -- followup in the newsgroup]

On Fri, 24 Aug 2012 17:47:51 +0000 (UTC),
(Andrew Gabriel) wrote:

It's also to check that both sides of the double check valve
are working

How would you test this? Remove the tap and apply water through the
"wrong" end with a hose pipe and if it comes out the drain hole, the
first valve is broken; if it comes out the "back" of the tap, both are
broken?

I've never heard of testing them before. Is it done on installation or
is it supposed to be done annually?

In article ,
Fred writes:
On Fri, 24 Aug 2012 17:47:51 +0000 (UTC),
(Andrew Gabriel) wrote:

It's also to check that both sides of the double check valve
are working

How would you test this? Remove the tap and apply water through the
"wrong" end with a hose pipe and if it comes out the drain hole, the
first valve is broken; if it comes out the "back" of the tap, both are
broken?

I've never heard of testing them before. Is it done on installation or
is it supposed to be done annually?

I don't seriously believe anyone does, hence the sarcy comment.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]