Good diagram and description of operation of a torbeck diaphragm valve anyone?

Hi,
A friend of mine has a toilet with closely coupled system and overflow empties into the pan. After a fair amount of googling I think she has a bottom-supply torbeck type valve. We have carefully taken the thing apart and checked the diaphragm for tears or build up of crud. I have put it back together in the same order is I dismantled it and didn't cross threads etc. All I have succeeded in achieving is the valve does not shut the supply off at all when the float is up and the cistern overflows at a much higher rate. At least we understand (sort of) the problem - but for now the toilet is out of action - I have shut off the supply to that toilet.
Now I have seen many wordy description of how these should work but does anyone know of a link to a site that shows exactly the operation and the areas where the valve can fail? The only part that seems relevant to creating the seal to shut off the supply is the diaphragm valve with a tiny, delicate pin type thing that passes through the middle of the diaphragm. The following seems a pretty good image of the diaphragm
https://www.choiceful.com/choiceful-id-5999-Armitage-Shanks-Diaphragm-Washer.html
but I'm not sure it is the correct one. The valve mechanism has no manufacturer stamp - just "Quiet Ball Valve" moulded into it.
Could the problem be something to do with the tiny pin hole in the top of the valve body?
Can anyone provide any more info on the operation of these or advice on replacing diaphragms or replacing the whole unit?
Thanks
Clive
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Clive wrote:

Just replace it. What do they cost 10 - 15?
Not worth trying to repair it. Remove the old one, take it to a proper plumbing shop & get a direct replacement.
--
Dave - The Medway Handyman
www.medwayhandyman.co.uk
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My view is that replacing a washer / diaphragm wastes less material and is a whole lot less disruptive than replacing the whole device. that of course assumes it was the diaphragm that caused the problem.
Unfortunately my purist bubble was burst in that I couldn't get a replacement diaphragm.
We bought a replacement Torbeck, fitted it - and even when the float was up the flow wasn't stopped or restricted one bit.
So off came the Torbeck and an order for a FluidMaster was placed. The Fluidmaster seems a more robust bit of kit.
The FM is installed and works fine in that the water flows into the cistern and cuts off totally when the float is raised. Also the water filling from the base of the device is almost silent.
Two problems
I fitted the flow restrictor and the filling is very slow - so I will have to take that out. I don't know if the cistern supply is tank-fed or direct mains.
I put PTFE tape around the brass pipe at the bottom of the FM and replaced the washer in the flexible hose. The washer looks like it is made of fibre rather than rubber. I carefully cleaned the place where the washer was to be seated. I carefully tightened everything to ensure no threads were crossed and I didn't over tighten - barely a quarter turn with a spanner after hand-tightening. There is a *very* slow leak from the "bottom" of the hose nut - as if the water is somehow coming "around" the new washer. I'm hoping that the leak will seal as the water here is hard. Any ideas of some step I missed in assembling and fitting the FM tha might mean the leak will remain? I will probably have to dismantle anyway to remove the flow restrictor.
Clive
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