Variable-flow pumps of the drum piston type

Claim 1

IN A PUMP OF THE DRUM PISTON TYPE COMPRISING A HOUSING HAVING A TRANSVERSE WALL AND PROVIDED WITH AN INDUCTION PASSAGEWAY AND A DELIVERY PASSAGEWAY OPENING ON SAID TRANSVERSE WALL OF SAID HOUSING, A ROTOR MOUNTED FOR ROTATION ABOUT AN AXIS IN SAID HOUSING AND HAVING A LATERAL FACE IN CONTACT WITH A CORRESPONDING SURFACE OF SAID TRANSVERSE WALL AND BORES OPENING ON SAID LATERAL FACE, PISTONS DISPOSED FOR RECIPROCATION IN SAID BORES AND HAVING EACH A PART-SPHERICAL HEAD OUTSIDE SAID ROTOR, A CAM HAVING A FLAT FACE COOPERATING WITH SAID HEADS OF SAID PISTONS FOR CONTROLLING THE MOVEMENT OF SAID PISTONS IN SAID ROTOR, A SHOE MOUNTED ON EACH OF SAID HEADS OF SAID PISTONS AND HAVING A FLAT FACE RESTING AGAINST THE SAID FLAT FACE OF SAID CAM, A RETAINING PLATE FOR BIASING SAID SHOES AGAINST SAID CAM, A SPRING BIASED MEMBER AXIALLY AND SLIDINGLY MOUNTED IN SAID ROTOR, SAID SPRING BIASED MEMBER AND SAID PLATE PROVIDING CONTACTING SURFACES BETWEEN THE SPRING BIASED MEMBER AND THE PLATE, SAID CONTACTING SURFACES PROVIDING GROOVES AND PROJECTIONS FITTING IN SAID GROOVES FOR POSITIVELY DRIVING THE PLATE VIA THE SPRING BIASED MEMBER.