Bill, what you are looking for is commonly known as a 'line lock'. Drag racers have used them for years but have since gone from manual actuated to solenoid ones. There was a time when the Jamar line lock valve was available from J.C. Whitney. But, I did a quick google and see it mentioned that they don't sell it anymore........I am investigating installing a stop valve in the main line so I can use it as a parking brake. I am currently searching for an appropriate valve. So far the best option is from Matco mfg - http://www.matcomfg.com/PARKINGBRAKEVALVESINGLESIDED-idv-3580-8.html. It’s nice and maybe the fallback, but I’m looking a little more friendly to the pocket book.