Cylinder 1 rotates about fixed axis A. Piston 3 reciprocates in cylinder 1 and has rod b with rollers a at its ends. The internal surface of the housing is profiled in such a manner that all the chords passing through axis A are of equal length. This shape may be, for example, a cardioid. When cylinder 1 rotates, rollers a roll around inside the housing and reciprocate pump piston 3.
$3817$LHP,RP$