Lantraxco, you should know by now I overthink everything. At least the stuff I post here. It's just a bad habit from an anal machinist. Enjoy your popcorn. Hope you brought enough for everyone ;-) And Shimmy1, yes, I tend to be overly analytical with a great many things. And I know it bogs me down. Usually though, if I spill my thoughts here, someone clears away the fog for me and I see the correct solution out of the myriad odd possibilities my mind has cooked up.
WillieB, I think that is how this particular trailer is set up to operate, only with a single, multistage cylinder. Just pressure in to lift, and a dump valve to lower. Nothing more. It has to be, since there is only a single hose. They drove off with it before I could spend much time with it, so I can't say I traced the hose to see where it went. For all I know there is a pneumatic valve on the trailer that changes everything. I wasn't focusing on the air lines between the truck and trailer other than the normal brake lines.
Shimmy1, yes, there is a reason I can't just put another valve into this equation. There may be 10 trucks involved. I only have one trailer to rig out to work. All of the other dump trailers, live bottoms, etc, are set up for two hoses. I have been asked if there is a way to make this one trailer operable with any one of the available trucks. I could never convince them, or myself, that spending the time and money to modify all the possible trucks would be justifiable. It would be cheaper and quicker to change this trailer to a double acting cylinder. Then come the liability issues which will prevent me personally from doing that. If it was just changing dump beds from another truck, then sure, change to a suitable valve, no problem and there would be no thread here. I was hoping to just find an easy way to do something safe with the second, un-needed "down" hose. Simple as that. I think that buried in this thread, the answer is here.
It's the weekend, and Monday I'll talk to the guy who actually owns all this and see what he really wants to do. His ops guy is the one that started all of this while his boss was out of town. I don't work for him, I work for the owner. This started, as I stated earlier, to avoid insp/ins/regis on a trailer that may see only seldom use. It may stop Monday.