Rotor 1 rotates about fixed axis A and has guides a with perpendicular axes. Reciprocating in guides a are pistons 4 which have rollers 2. These rollers roll and slide along the groove of fixed face cam 3. The centre line of the groove is a circle with its centre at point O, located eccentrically with respect to axis A. When rotor 1 rotates, pistons 4 reciprocate and deliver a fluid, drawing it in and discharging it along passages which are not shown.
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