I don't know for sure how this system works, it may have 2 valves. The Dearborn bucket has a mechanical trip. The single action cylinders expand when the valve is activated and release when the valve is closed. In the case of the old 8N, this action takes place by putting a line into the system after the 3 pt. relief pop valve and chaining down the 3 pt. hitch lift arms. When you activate the system, the relief valve pops and the pressure goes to the loader cylinders.