JT...
The mechanism is nearly identical, it's just a matter of where the air is injected in to the tube. On the drops, the air is injected at the bottom, forcing the piston up through the tube, and therefore pulling the carriage down. The shots are the exact opposite.
There's a great article on Hydraulics and Pneumatics, but they haven't posted it to their Web site.
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Jeff
Webmaster/Guide to The Point
Millennium Force laps: 39