Abstract: An unloader includes a first volume bottle with a cavity formed therein of predetermined volume, and a port in the forward end with a plug operably mounted to selectively open and close the port. A second volume bottle is stacked on the first volume bottle and has a port in the forward end with a plug operable to open and close the second bottle port. The second bottle is arranged such that the second port will fluidly connect the first and second bottles. Actuators are connected to the plugs in the first and second bottles to selectively open only the first bottle or both bottles together, to thereby provide a two stage internal clearance for the reciprocating compressor cylinder.