Re: D&RGW tender air valves

Brian in conjuntion with what you just mentioned regarding straight air, I remember looking in one of my old books that showed the earliest form of triple valve for cars. It had a 3 way cock built into the body of the triple valve. One position was for automatic air, another position bypassed the triple valve so the the train line was connected directly to the brake cylinder so the car could be used with a locomoitve equipped with straight air, but not automatic. The 3rd position of the cock was the cut out position. I wonder if the triple valve you mention on the locomotive and tender was simply the same as above used in a slightly different application.
It would be neat if someone would research and write a book on the evolution of the air brake covering these many inovations in a time line context. Or is there such a book out there?