I understood the old float ball valve type with the slider that carried a
washer against the nozzle, and the newer variations on that which used a
diaphragm, but this flat has some modern contraption and I'm having
trouble understanding how it works.

Close coupled, bottom entry, float operates a lever on the top that
closes an air hole that I believe leads to water flowing through a hole
in the middle of the diaphragm then forcing the diaphragm closed on the
basis that the water pressure is acting on a larger area on one side of
the diaphragm than the other.

The hole in the middle of the diaphragm has a small plastic insert thingy
in it which I think is meant to be a one way valve.

The float sits in a cup that drains through a one way flap when the
cistern empties so that as the cistern fills, the float doesn't rise
until the water level reaches the rim of the cup, I believe this is so
that the cistern refills quickly until it reaches the stop point, as the
float valve only moves when the cistern is almost full. This cup is part
of the inlet tube, and the float surrounds the inlet tube.

Can't find anything on the web that describes this sort of valve
operation, which means I'm guessing as to how it actually works and
unsure about how to try and fix it. As far as I can tell there are two
rubber parts, the diaphragm with the plastic thingy that might be a one-
way valve in the middle, and the little bung that gets pressed down on
the top hole as the float rises.

Damn thing leaks for about 20 - 40 minutes after flushing before it
settles down. I've had it all apart once and made sure nothing appears to
be scaled up, diaphragm not split etc.

I'm unable to see any indication of the manufacturer on the device. There
are similar looking items in the screwfix catalogue, but nothing that
looks the same.
--
Denis McMahon,

"Denis McMahon" wrote in message
...
I understood the old float ball valve type with the slider that carried a
washer against the nozzle, and the newer variations on that which used a
diaphragm, but this flat has some modern contraption and I'm having
trouble understanding how it works.

Close coupled, bottom entry, float operates a lever on the top that
closes an air hole that I believe leads to water flowing through a hole
in the middle of the diaphragm then forcing the diaphragm closed on the
basis that the water pressure is acting on a larger area on one side of
the diaphragm than the other.

The hole in the middle of the diaphragm has a small plastic insert thingy
in it which I think is meant to be a one way valve.

The float sits in a cup that drains through a one way flap when the
cistern empties so that as the cistern fills, the float doesn't rise
until the water level reaches the rim of the cup, I believe this is so
that the cistern refills quickly until it reaches the stop point, as the
float valve only moves when the cistern is almost full. This cup is part
of the inlet tube, and the float surrounds the inlet tube.

Can't find anything on the web that describes this sort of valve
operation, which means I'm guessing as to how it actually works and
unsure about how to try and fix it. As far as I can tell there are two
rubber parts, the diaphragm with the plastic thingy that might be a one-
way valve in the middle, and the little bung that gets pressed down on
the top hole as the float rises.

Damn thing leaks for about 20 - 40 minutes after flushing before it
settles down. I've had it all apart once and made sure nothing appears to
be scaled up, diaphragm not split etc.

I'm unable to see any indication of the manufacturer on the device. There
are similar looking items in the screwfix catalogue, but nothing that
looks the same.
--
Denis McMahon,

You generally find that devices like this have a mall hole in the diaphragm
(or nearby) which lets water into a chamber that powers the diaphagm valve
shut.
Dribbling as you describe is the symptom of this small hole being blocked.
It's small enough to be overlooked.

Best description I have ever read.

I had a moulding defect on the flushing diaphragm that caused problems.

On Tue, 21 Apr 2015 07:02:34 +0000, DerbyBorn wrote:

Best description I have ever read.

I had a moulding defect on the flushing diaphragm that caused problems.

Seems there was a very small split in the diaphragm that made itself much
more visible the next time I pulled it out. Looking at various images
found by googling "bottom entry ball valve diaphragm" led me to believe
that the magic incantation was "armitage hushflo", and a short stroll to
the neighbouring B&Q saw it fixed for GBP 1.57.

--
Denis McMahon,

On Tuesday, April 21, 2015 at 1:22:48 AM UTC+1, Denis McMahon wrote:
I understood the old float ball valve type with the slider that carried a
washer against the nozzle, and the newer variations on that which used a
diaphragm, but this flat has some modern contraption and I'm having
trouble understanding how it works.

Close coupled, bottom entry, float operates a lever on the top that
closes an air hole that I believe leads to water flowing through a hole
in the middle of the diaphragm then forcing the diaphragm closed on the
basis that the water pressure is acting on a larger area on one side of
the diaphragm than the other.

The hole in the middle of the diaphragm has a small plastic insert thingy
in it which I think is meant to be a one way valve.

From your description, I think the technical term is a pilot-operated diaphragm valve. The small valve vents pressure from one side of a diaphragm, which allows it to open; in effect the water is stopped by its own pressure. Googling should provide details.

I had something similar fitted to a softened water storage tank, a tiny float valve operated a massive (2", or so ISTR) diaphragm valve, and kept it fully open or fully closed. It worked.