Clif,Ian & Jesse, Many thanks for your response on this matter. I think I will go with ptfe. If I am still sane after making these here piston valves I will turn up some glands out of solid ptfe. Regards, Barrie MODEL ENGINEERING DISCUSSION LIST. To UNSUBSCRIBE from this list, send a blank email to, modeleng-request@xxxxxxxxxxxxx with the word "unsubscribe" in the subject line.