Connecting rod 2 is connected by turning pairs to slider 3 and to rocker arm 1 of four-bar linkage ABCD. Rocker arm 1 oscillates about fixed axis A, reciprocating the piston through connecting rod 2. The lengths of the links of linkage ABCD are selected so that lengths A͞B plus B͞C are only slightly more than lengths A͞D plus D͞C. As a result, rocker arm 1 has a large angle of swing, providing a long stroke for slider 3. Rocker arm 1 is balanced with respect to axis A.
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