Torbeck valve - how does it work?

We have slimlines (came with the house) and a special float and arm on one of them shattered. I replaced it with a Torbeck years ago.

The onoly problem is that sometimes it doesn't shut off properly and the overflow starts to run. Always caused by a tiny bit of grit blocking the bleed hole under the arm [1]. Take it apart, compressed air, job done.

replying to Bob Eager, JD2 wrote: Finally found the problem with the Torbeck valve. Has anybody else found the SECOND rubber? If you carefully pries of the lever arm you will see a black rubber washer in the arm. It is only about 3mm in diameter. Look at the surface through a magnifying glass and there may be ware makes on it. This is the seal that closes off the bleed air valve. If you find a supplier of a replacement let me know. Meantime pries out the washer and reverse it. Careful it will spring out and disappear for ever. Reassemble and have a quiet nights sleep. JD2