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Tuesday, July 13, 2010

Vane, Gear, and Lobe Pumps

Pumping with a vane, gear or lobe pump begins with the rotating and stationary parts of pump defining a given volume or cavity of fluid enclosure. This enclosure is initially open to be pump inlet but sealed from the pump outlet expands as the pump rotates. As rotation continues, the volume progresses through the pump outlet.

Depending on the particular pump, there can be more than one cavity in existence at any one time. As this happens, fluid also fills the clearances between the pumping elements and fluid. Rotation continuous and the cavities progress, moving fluid along the way. Soon a point is reached when the seal between the capture fluid volume of captured fluid out of the pump. While this happening, other cavities are simultaneously opening at the inlet post to receive more fluid in a continual progression from suction to discharge parts.

With rotary pumps, a driver turns one shaft and rotor assembly, which in turn physically meshes with another to form the cavities that move the fluid. This is known as an untimed arrangement. For some applications, however, there would be problems with gears, lobes, or screw meshing this way. For instance, stainless steel gears will gall and seize if rubbed against each other. High wear rates will also occur if any dirt is trapped between the meshing lobes of a lobe pump, regardless of their material, or if a pump with meshing gear.

The circumvent of this, the timed pump was developed. It uses timing gears physically located outside the pumping chamber to transmit torque between the pump shaft and synchronize the pumping elements relative to each other. By preventing them from contacting each other, they eliminate many of the problems of dirty fluids, material compatibility, and dry running. Most lobe pump are built this way, and gear pump can be timed or untimed as well.

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