What are your thoughts about the best way to stop air cylinder with a light curtain application? Lets say it's mounted vertically and is connected to a couple hundred pound load (i.e. enough to fall and hurt somebody or something).

Pneumatic valve choices and issues that I have heard of but I really don't fully understand the impact of them all:

1) 3-position-center-open.
---->The load will fall when the light curtain is broken.
---->Tooling might slam at the top position once system is re-energized.

2) 3-position-center-open with pilot-operated-check-valve on the bottom port of the cylinder
---->Response time to stop load might not be fast enough for application.
---->Load could drift up.
---->Tooling might slam at the top position once system is re-energized.

3) 3-position-center-blocked or pilot-operated-check-valves at both ends of the cylinder.
---->Response time to stop load might not be fast enough for application.
---->Cylinder might drift
---->Cylinder is locked in position. It will take a crowbar to move it, or you'd have to remove the pilot-operated-check-valves.

4) 3-position-center-pressurized.
---->Load will drift towards the rod end of the cylinder because the rod side of the piston has a smaller surface area, therefore will have less force than the force on the non-rod side of the piston.

5) 3-position-center-pressurized where each side of the cylinder is pressurized with a different pressure. When setup correctly it will balance the load by compensating for the different surfaces areas on the piston (i.e. rod side will need a higher pressure since it has a smaller surface area).
---->Response time very good
---->Complex and could be difficult to plumb.

Just curious what others have to say about this issue.

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