Air piston with constant outlet flow rate regardless of applied force 2

[Eric26]

I am working on a design where I am trying to use a dual-acting air piston to slow down a downwards moving weight. Say the weight can be anywhere between 50 and 200 pounds. The difficult part is that the downstroke of the piston must move down at roughly the same rate regardless of the size of the weight. This means that the outlet air exhaust flow rate must be constant, even though the pressure inside the chamber will be higher with larger weights. The upstroke motion must be unimpeded except for the force of the weight, but don't focus too much on that part.

If I just had an orifice at the outlet, then the flow rate would obviously still change based on the pressure. I could also just use some sort of flow-control valve at the outlet, and open it up more or less depending on the weight. The problem is that based on my design requirements I need the valve to open and close automatically rather than manually, and I can't use any electronic equipment (it needs to be completely mechanical).

Any suggestions or input at all would be appreciated!

 

[3DDave]

Because the weight varies the initial compression of the gas will vary, so the initial motion will vary even before air leaves the cylinder.

The best I can think of is to mount the cylinder in such a way that there is a spring under it allowing the cylinder to move based on the weight and a linkage between the mount and the cylinder to operate a needle valve that closes with greater weight. Depending on the needle valve the spring could be rather stiff and not much increase the initial movement.

 

[1503-44]

It may also need to be temperature compensated, if your range of operating temperatures is wide.

I think your valve will have to be controlled somehow by piston travel rate to stand any chance of working as you want and it will be challenging in any case, since lower temperatures and higher pressures will release many times more mass than when at normal temperature and lower loads. Responses will vary considerably. Maybe a series of relief valves with different orifice sizes, each set to open or close at a different pressure range could approximate what you want. That technology is beyond my pay grade, but heck, it might actually work, now that I think about it.

Otherwise I can only get as far as a very hazy view of some kind of load balance spring can that applies constant force to the piston no matter what load is applied to the palet and you still have the independent potential temperature problem.

https://whatispiping.com/spring-hanger-selection/

You stand a chance of making it work with hydraulics, but getting gas to do anything on a constant basis, esp with no electronic compensation, that's a big problem.

A black swan to a turkey is a white swan to the butcher ... and to Boeing.