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Rotary Pumps

In their many forms, these mechanisms are distinguished from centrifugal pumps in that they are positive displacement units which have close clearance not only between their moving parts but also between the internal assemblage and the casing which surrounds it. Rotary pumps have no valves, and barring undue leakages they can deliver a reasonably constant volume of liquid against pressures ranging from low to high. Their greatest field of application is in pumping fuel oils and other liquids which have viscosity enough to prevent leakage and also some properties of lubrication.

The figure illustrates a longitudinal section of a roller pump. When pump is in operation, the rollers held within recesses of the revolving rotor tend to move outward by action of centrifugal forces. As indicated, the liquid handled is entrapped between the rollers and the bottom of the casing and is discharged under pressure at the outlet connection.

 

 

The internal gear type of pump has an overhung rotor which is forged integral with its shaft which is located at the center of the casing. The rotor has openings about its periphery which form nine internal teeth. Within the rotor is an idler gear with seven external teeth which mesh with those of the rotor. The idler gear is mounted upon a stud attached to the casing cover. The rotor and the idle gear revolve about different centers, so that the idler gear is eccentric with the rotor. The crescent shaped piece at the bottom of the idler gear serves as a seal, and the liquid entrapped between the gear teeth is forced out against the discharge resistance.

Water pump, Volute, turbine pump, axial flow units.

 

High pressure vacuum pump, Rotary pumps.