I used a C model Ford with a Bartlett 5th wheel for a yard truck for a few years. It had a 534 engine in it that used several gallons of gas just to build up air pressure. It had a valve exactly like John describes for the spring brakes. However, it had a small chrome trolly valve which we didn't use because we only charged the emergency line to move trailers. The vehicle had originally been used as a truck tractor and the lever was used as a trolly valve for the trailer brakes. But I was not the original owner and I don't know what was original. I'm not sure if it even had spring brakes from the factory.
