PM620, PM622, PM820, PM822 and PM825 Cold Planer Machine System Caterpillar

Illustration 1	g06073042
Engine Compartment (1) Auxiliary pump (2) Pump control valve

Auxiliary hydraulic pump (1) is splined to the conveyor pump. The pump is located in the engine compartment. Pump control valve (2) is located at the bottom of the pump. These components are accessed through the right engine compartment door, or from an access panel above the cutter chamber.

Auxiliary hydraulic pump (1) draws oil from the hydraulic tank through a suction screen. Pump supply oil is sent to the cutter box valve and then distributed to other auxiliary control valves.

The ports on the auxiliary pump are marked for identification. The pump draws oil from the hydraulic tank through port"S". High pressure supply oil exits the pump at port"B". The case drain line is connected to port"L1".

Illustration 2	g06259198
Auxiliary Hydraulic Pump (2) Pump control valve (3) Pressure compensator spring (4) Pressure compensator spool (5) Orifice (6) Orifice (7) Servo piston (8) Bias spring (9) Swashplate (10) Slipper pad (11) Slipper retainer (12) Piston (13) Barrel assembly (14) Valve plate (15) From tank (16) To cutter box valve

This cross-sectional view of the auxiliary pump shows the major pump components. When the auxiliary pump is at rest, bias spring (8) forces swashplate (9) to the maximum angle. Engine rotation turns the pump input shaft, which then rotates barrel assembly (13).

Barrel assembly (13) and pistons (12) make up the rotating group. The pistons in the group rotate with the barrel assembly. Piston slipper pads (10) allow the pistons to follow the angle of swashplate (9).

As slipper pads (10) follow the angle of swashplate (9), the pistons move in and out of barrel assembly (13). As a piston moves out of the barrel assembly, oil from the hydraulic tank is drawn into the piston chamber. As a piston moves into the barrel assembly, pressure increases and oil is forced out of the piston chamber.

The pump supply oil flows into pump control valve (2). Supply oil acts against pressure compensator spool (4) in opposition to pressure compensator spring (3). As auxiliary hydraulic circuits are used, the pressure compensator spool maintains pump output at a constant pressure.

When pump supply pressure reaches 21000 kPa (3045 psi), pressure compensator spool (4) moves against the spring force. This movement opens a passage for pump supply oil to flow into the chamber of servo piston (7). Pressure in the servo piston chamber causes the servo piston to move swashplate (9) against the force of bias spring (8). This movement reduces the angle of the swashplate.