950G Series II Wheel Loader Caterpillar


Vane Pump

Usage:

950G II AXR


Vane Pumps

Vane pumps are positive displacement pumps. The pump output can be either a fixed vane pump or a variable vane pump.




Illustration 1g01062415

Both the fixed vane pumps and the variable vane pumps use common part nomenclature.

Each pump consists of the following components:

(1) housing

(2) cartridge

(3) mounting plate

(4) mounting plate seal

(5) cartridge seals

(6) cartridge backup rings

(7) snap ring

(8) the input shaft and bearing

The cartridge consists of the following components:

(9) support plates

(10) ring

(11) flex plates

(12) slotted rotor

(13) vanes

The slotted rotor is turned by the input shaft. The vanes move in and move out of the slots in the rotor, and seal on the outer tips against the cam ring. The inside of the fixed pump displacement ring is elliptical in shape. The inside of the variable pump displacement ring is round in shape. The flex plates seal the sides of the rotor and the ends of the vanes. In some lower pressure designs, the support plates and the housing seal the sides of the rotating rotor and the ends of the vanes. The support plates are used to direct the oil into the proper passages in the housing. The housing directs the flow in and out of the vane pump. The housing also provides support for the other parts of the vane pump.

Vanes




Illustration 2g01062416

The vanes are initially held against the cam ring by centrifugal force that is created by the rotation of the rotor. As the flow increases, the resultant pressure that builds from the resistance to that flow is directed into passages in the rotor beneath the vanes (1). This pressurized oil beneath the vanes keeps the vane tips pushed against the cam ring to form a seal. To prevent the vanes from being pushed too hard against the cam ring, the vanes are beveled back (arrow) in order to permit a balancing pressure across the outer end.

Flex Plates




Illustration 3g01062417

The same pressurized oil is also directed between the flex plates and the support plates in order to seal the sides of the rotor and the end of the vanes. The size of the seal area between the flex plate and the support plates is what controls the force that pushes the flex plates against the sides of the rotor and the end of the vanes. The kidney shaped seals must be installed in the support plates with the rounded o-ring side into the pocket and the flat plastic side against the flex plate.

Vane Pump Operation




Illustration 4g01062419

When the rotor rotates around the inside of the cam ring, the vanes slide in and out of the rotor slots in order to maintain the seal against the cam ring. As the vanes move out of the slotted rotor, the volume between the vanes changes. An increase in the distance between the cam ring and the rotor causes an increase in the volume. The increase in volume creates a slight vacuum that will allow the inlet oil to be pushed into the space between the vanes by atmospheric pressure or tank pressure. As the rotor continues to rotate, a decrease in the distance between the ring and the rotor causes a decrease in the volume. The oil is pushed out of that segment of the rotor into the outlet passage of the pump.

Balanced Vane Pump




Illustration 5g01062420

The balanced vane pump has an elliptical shaped cam ring. This shape results in the distance between the rotor and the cam ring increasing and decreasing twice for each revolution. The two inlets (1) and two outlets (2) opposite each other balance the forces against the rotor. This design does not require large bearings and housings in order to support the rotating parts. The maximum operating pressure for vane pumps is 27600 kPa (4003 psi). Vane pumps that are used in mobile hydraulics have a maximum operating pressure of 20700 kPa (3002 psi) or less.

Variable Vane Pump




Illustration 6g01062421

Variable output vane pumps are controlled by shifting a round ring back and forth in relation to the rotor centerline. Variable output vane pumps are seldom used in mobile hydraulic applications.

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