I recently bought a 1953 NAA with a hydraulic valve under the seat that has a single quick disconnect. There is a small copper tube connected to an adjacent port that loops back to the valve body. I'm guessing this is set up to operate a single-acting cylinder but I'm not very knowlegable about hydraulics and can't find much information about this system. Can anyone tell me what the small copper tube does and if it can be removed and that port used with a double-acting cylinder? Any information would be appreciated.