Abstract: A proportioning pump for automatic fluid analysis apparatus comprising a base having an open chamber formed in its top, a drive shaft supported in the open chamber, and a platen member that closes the top of the open chamber. A pair of roller cage assemblies each have primary bores in their end plates allowing them to be mounted on the drive shaft. The end plates are pinned to the drive shaft so that they rotate as one. Spaced outwardly a predetermined radius from the longitudinal axis of the primary bores are a plurality of secondary bores whose longitudinal axes describe circles in the laterally spaced end plates. Roller rods are journaled in the secondary bores. The outer perimeter of each of the roller rods describes an arc of a predetermined radius from the axis of the primary bore when the roller cage assembly is rotated about its longitudinal axis.