On Sun, 24 Jan 2010 16:19:45 +0000, YAPH wrote:

On Sun, 24 Jan 2010 15:48:48 +0000, Bob Eager wrote:

but how do the things actually work - it's not obvious from looking at
mine

Black magic, I always think. Most of the DIY books have an explanation.

Indeed :-)

It's what's called an equilibrium valve. The basic principle is that
water pressure bears on both sides of the rubber diaphragm but there's
more surface area exposed to the water on the side that presses the
diaphragm against the inlet shutting off the water flow. But on that
side there's a tiny hole - the one you see which gets covered by the
tiny rubber bung attached to the float arm. When the float drops and
uncovers the hole it takes away the pressure holding the valve shut and
water runs through the valve, filling the cistern until the float rises
and closes the hole whereupon the pressure on that side closes the valve
again.

Neat, huh? ;-)

Until the hole gets blocked...they are very prone to dirt, etc. When
they've been repairing water mains nearby, or when they suddenly decided
to fit an external stoptap without telling us, dirt got in and buggered
it up...!



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