Abstract: The transmission comprises a hollow input member (1) and a coaxial output member (2) supported for rotation relative to the input member. A positive displacement pump comprises a cylinder block (12) secured to the input member and a rotor (16) which is journalled on an eccentric pin (17) and which drives the pump pistons (15). A positive displacement motor comprises a stator part (6) secured to the input member and a rotor part (5) secured to the output member. The motor cylinders (8) are supplied with hydraulic liquid from the pump through duct means (35, 37, 39) in a disc-shaped control member (22) journalled on the eccentric pin (17) and rotating together with the pump rotor (16). Return flow from the motor to the pump occurs through a space (28) which within the input member surrounds the control member (22) and which communicates with each pump cylinder (14) during the suction stroke of the associated pump piston (15).

Abstract: In a stationary skimmer disc for withdrawing a liquid phase from a centrifuge there are formed one or more liquid discharge ducts each having an inlet at the outer periphery of the disc and at least one outlet located closer to the center of the disc. From a region of the flow path of the discharged liquid, where the static liquid pressure, during operation of the centrifuge, exceeds the static pressure at the inlet to the discharge duct or ducts, a by-pass duct having a throttling means intermediate its ends leads back to each of said inlets.