"BillP" wrote in message
...

"Alan Campbell" wrote in message
om...
Hi all,

Whats the difference between a part 1 :-

http://www.screwfix.com/app/sfd/cat/...14542&ts=32264

and a part 2

http://www.screwfix.com/app/sfd/cat/...11518&ts=32264

Alan

Hi Alan,

It's all to do with the air gap between outlet and water level when fitted
to the cistern. The airgap is required for backflow prevention. The part 1
valve has the outlet on the under side of the valve. This is not suitable
for fitting to WC cisterns where the inlet hole is at the same level as
the
overflow hole. In the event of the valve failing, the water level rises to
the overflow level and the outlet of the valve ends up under water, thus
the
required air gap for backflow prevention is lost. The part 2 valve has the
water outlet via an upstand. If this valve is fitted in a cistern where
the
inlet and outlet holes are at the same level, then in the event of an
overflow situation, the airgap is maintained.

In general if the inlet hole and overflow holes are at the same level then
Part 2 valve is required.

If the inlet hole is above the overflow hole and the airgap is maintained
in
the overflow situation then part 1 can be fitted.

A part 1 valve can be replaced with a part 2 valve with no problem.
But a part 2 valve can't be replaced with part 1 unless you first check
that
the air gap will be maintained in overflow situation.

Part 1 valves usually found on potable water cisterns, cold water tank in
loft.

Part 2 valves usually found on WC cisterns and CH feed/expansion tanks.

I usually find and almost always fit plastic valves to WC cisterns - the Y
fork at the end of the arm allows the float ball to be angled to one side or
the other which is usually necessary to get past the flush valve. You can
use brass part 2 valves, and in fact I did so with one today: one handy
thing with brass part 1 and 2 valves is that you can leave the 1/2" BSP tail
of the valve attached to the cistern and pipework and unscrew the big brass
nut coupling it to the valve body and just replace the body - including
replacing a part 1 with a part 2.