It is a combination of two slider crank mechanisms.
Crank shaft (one in violet and one in yellow) has two cranks and is connected to two sliders (in blue and in pink) by green conrods.
Working stroke (distance between the two sliders) is increased two times (if angle between the two cranks is 180 deg.) in comparison with mechanism of one crank.
STEP files of this video:
http://www.mediafire.com/download/fhe11y49ntg5r19/AirComprSTEP.zip
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