BOLT 9B6520 - Caterpillar

Non-Positive Displacement Pumps
Non-positive displacement pumps have more clearances between the moving and the stationary parts than positive displacement pumps. The extra clearance allows more oil to be pushed back between the parts as the outlet pressure (resistance to flow) increases. Non-positive displacement pumps are less efficient than positive displacement pumps because the output flow of the pump decreases greatly as the outlet pressure increases. Non-positive displacement pumps are generally either centrifugal impeller-type or axial propeller-type. Non-postive displacement pumps are used in low pressure applications. Some applications are automotive water pumps or charge pumps for piston pumps in high pressure hydraulic systems.Centrifugal Impeller Pump
Illustration 1 g01061997
The centrifugal impeller pump consists of two basic parts: the impeller (2) and the housing (3). The impeller is mounted on an input shaft (4), that has a solid disc back with curved blades (1) that are molded on the input side.Oil enters the center of the housing (5) near the input shaft and flows into the impeller. The curved impeller blades propel the oil outward against the housing. The housing is shaped in order to direct the oil to the outlet port.Axial Propeller Pump
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The axial propeller type pump is shaped like an electric air fan. The axial propeller is mounted in a straight tube. The axial propeller has an open blade propeller. Oil is propelled down the tube by the rotation of the angled blades.Positive Displacement Pumps
There are three basic types of positive displacement pumps: gear, vane and piston. Positive displacement pumps have much smaller clearances between components. This will reduce leakage and this will provide a much higher efficiency, when displacement pumps are used in a high pressure hydraulic system. The output flow in