Hi,
Try www.cla-val.com and surf to their "solution city". You will find pressure sustaining valves type 50-01 Series somewhere in the middle of the picture. With this type of valve there is hardly a limit to what you can do. I am however not sure if they have (or if you need) a PTFE...
Hi,
There is absolutely no reason not to use butterfly valves for a gas application, whereas knife gate valves are NOT a good choice. As indicated by jet1749 before, knife gate valves are good at "cutting" through media, and do not have a very low leakage rate as you might need for...