An Air Driven Gas Boosters consist of a large area reciprocating air drive piston directly coupled by a connecting rod to a small area gas piston. The gas piston operates in a high-pressure gas barrel section. Each gas barrel end cap contains high-pressure inlet and outlet check valves. The air drive section includes a cycling spool and pilot valves that provide continuous reciprocating action when air is supplied to the air drive inlet.

The animation shows a single stage booster pump with an air return, like the MIDI. The Expedition and ROB have a spring return on the non compression stroke.

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