Steam engine on compressed air

[Gordon]

I am trying to run a Corliss engine on compressed air using an airbrush compressor. My question is what am I missing in my calculations? The engine has 1.125 bore x 1.5 stroke. This calculates to 1.49 ci/stroke. Since it is powered both directions it should use 2.9 ci per revolution of the flywheel. The compressor is rated for 1 cubic feet per minute with 40 psi to 58 psi set points. 1 cf = 1728 ci. 1728/2.9 should result in 595 revolutions. It is turning the flywheel at probably 25 RPM and it shows no pressure on the gage. It runs on my shop compressor with at about 5-7 PSI. I realize that there are probably some leakage around the piston and the valves but this is far from the expected result. Other folks are running similar engines on airbrush compressors. Is there a problem with my calculations or is the compressor just not putting out the volume that is is rated for?