Heretofore in the art of pumping fluids and particularly liquids there have been employed gear pumps and fixed and variable volume vane pumps and piston pumps. One of the difficulties with prior art gear pumps is that they pump only a constant volume. Other problems include loss of efficiency due to wear. Normally variable volume vane pumps are inefficient. Piston pumps are the only practical pump designed to provide variable volume at high efficiency. These are the most costly due to close tolerance machining required. They are intollerant to fluid contamination.
Vane pumps may be provided for a variable volume delivery, however, they are inefficient due to the internal mechanism required for regulating eccentricity. They are inefficient because of the increased clearances required.
Heretofore in vane type pumps, the vanes as they laterally push fluids responding to an eccentric curvature of the casing experience considerable transverse stress upon the sides of the respective vanes which tend to tilt or bend the vanes causing increased friction particularly against radial movements of the vanes in responding to variations of the cavity radius. In the use of vane type pumps, these transverse stresses upon the vanes produce internal stresses which are transferred to the rotor causing early wear and breakdown due often to high unit loading forces transmitted to the rotor and vanes.