Take a look into this small, simple and genius TECHNIC MOC from Paul (Sariel).
IMHO, it beats all small TECHNIC sets, that LEGO have released in the past years.
Find these and more pictures at Paul's Brickshelf folder.
It features a closed pneumatic circuit, which allows it to operate without any pump or compressor. Like this other illustration on the left (click to enlarge and read), describing the working principle in use (taken from Paul's Brickshelf folder also).
See it at work at the video on the right.
Lots of fun and good playability for the size and amount of parts.
Certainly a great fit to make a Pallet series, as I suggest below. ;)