A planetary drive system that aligns four fluid ends for a pump or four compressor cylinders in the same plane, allowing for four fluid ends/compressor cylinders to be driven by one rotation of the pump's motor. Additionally, the planetary drive system is stackable to allow, for example eight, twelve, or other multiples of fluid ends or compressor cylinders to be driven while minimizing any reduction in output pressure. The chemical injection pump also includes threaded vents on the fluid ends to capture chemicals primed through the valves to avoid spillage and waste during the priming process. The air compressor cylinders also include pistons with enhanced vacuum actuation under a flexible inlet (e.g. flapper inlet).