Just to add a little more info: The flow controllers I've used are adjustable one-way valves. You would want to orient it so air would flow through it unrestricted when the Z moves up, and restrict it when it moves downward. They can be adjusted very finely. And come to think of it, a spring extend cylinder might work better,... a standard double acting cylinder might work to since the area on the two sides of the piston isn't equal due to the rod on one side of it. Probably wouldn't be much net positive lift in normal size cylinders.