Compressed gas engine

A compressed gas engine comprising:

• a first engine module comprising:
• a first crankshaft;
• a first set of piston assemblies operatively coupled to the first crankshaft and comprising a first piston assembly having a first diameter and a second piston assembly having a second diameter;
• a second set of piston assemblies operatively coupled to the first crankshaft and comprising a third piston assembly having the first diameter and a fourth piston assembly having the second diameter, the second set of piston assemblies positioned on the crankshaft opposite the first set of piston assemblies such that the piston assemblies of the first set of piston assemblies and the piston assemblies of the second set of piston assemblies having the same diameter are aligned;
• and
• a first valve assembly fluidly coupled to the first set of pistons and the second set of pistons and configured to control a flow of compressed air through the first engine module;
• and
• wherein:
• an open-side cavity of the first piston assembly is fluidly coupled to and receives compressed air from a compressed air source;
• and
• a rod-side cavity of the second piston assembly is fluidly coupled to and receives partially expanded compressed air from a rod-side cavity of the first piston assembly.