[jspatz1]

The cylinder will consume no air after it is extended, the pressure holding it is static. You will want to maintain extend pressure (valve actuated) so the holding force is maintained. When retracted (valve exhausted) the cylinder will be vented and the spring will supply the only return force. A spring return cylinder consumes 1/2 of the air (actually a little more than 1/2 due to the rod volume) of a double-acting cylinder.