On Tue, 04 Jun 2013 18:49:56 -0400, Tom Gardner Mars@Tacks
wrote:
snip
push a 5/8" rod two inches with about 600 lbs of pressure.

Check out air brake actuators for HD trucks/trailers.

one place to start

http://www.easternmarine.com/Air-Bra...ers-Diaphrams/