Thank you, now it is perfectly clear. It might be a bit more difficult to build, but very suitable for one new design, that I have in mind for this summer.

I am not using a "normal" piston valve which opens by venting the pilot volume. My design is basically this: https://www.spudfiles.com/spud_wiki/index.php?title=File:QDV_parts.JPG Yesterday I experimented with o-rings a bit and ended up with o-rings whose outside diameter is a full mm more than barr...

I have built a test 20 mm test device with QDV. And it leaks badly. My piston is turned from a polyamide / silon rod. The diameter of the piston is 19,75 mm and it slides perfectly in the pipe (which is made of aluminum). The lands have diameter 16 mm and I use 17 x 1,5 o-rings as free-floating seal...