Guys, Does anybody know how automatic drain cocks work? I know GW locos had pressure relief valves on the cylinders, but I didn't think they were the same thing. When I asked at the club I got a variety of garbled messages, but nothing very clear. TIA JohnP 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.