BOLT 0878442 - Caterpillar

Illustration 1 g03715698
Right Side of Machine (1) Front-wheel assist pump (2) Port "S" (3) Port "X" (4) Port "B" (5) Pressure compensator spool (6) Flow compensator spoolThe ports on front-wheel assist pump (1) are labeled for identification. The following describes each port on the pump:
Pump inlet - port "S" (2)
Pump case drain - port "L2"
Load-sensing port - port "X" (3)
Pump outlet - port "B" (4) The pump is equipped with a compensator valve. The pump compensator valve maintains pump pressure and flow at a level adequate to fulfill the system load and flow needs. The compensator valve contains flow compensator spool (6) and pressure compensator spool (5).
Illustration 2 g03715704
Cross Section of Front-wheel Assist Pump (3) Port "X" (5) Pressure compensator spool (6) Flow compensator spool (7) Orifice (8) Orifice (9) Flow compensator spring (10) To control valve (11) Orifice (12) Orifice (13) Pressure compensator spring (14) Swashplate (15) Bias spring (16) Bias piston (17) Actuator piston (18) Valve plate (19) Slipper (20) Slipper retainer (21) Piston (22) Barrel assembly (23) From tankNote: The above illustration shows the pump operating at full flow at a pressure less than maximum.When the input shaft is rotated, barrel assembly (22) turns. Pistons (21), which are installed in the barrel assembly, also turn with the barrel assembly. One slipper (19) is attached to each piston. The slippers are held against swashplate (14) by slipper retainer (20). Slippers (19) allow pistons (21) to follow the angle of swashplate (14) as barrel assembly (22) rotates. As the slippers move down the swashplate ramp, the pistons on the downhill side of the swashplate are pulled out of the barrel assembly. This action draws oil through valve plate (18) and into the piston bore in the barrel assembly. When a slipper reaches the bottom of the swashplate ramp, rotation of the input shaft forces the slipper to move up the ramp. Now, the angled swashplate pushes the piston back into the barrel assembly. This action pushes oil out of the piston bore, through the valve plate, and into the output port.The angle of swashplate (14) determines how much oil is drawn into each piston bore. The angle therefore determines how much oil is pumped out of each piston bore per revolution of the input shaft. Greater swashplate angles pull more oil into the pump and discharge more oil through valve plate (18) .Before the engine is started, bias spring (15) forces swashplate (14) to the maximum angle. As the engine is started, the pump immediately generates flow. The pump draws oil from the hydraulic tank through a screen. The pump delivers oil to pressure compensator spool (5), flow compensator spool (6), and control valve (10). The pump receives a load sensing signal from the control valve. This signal is sent to the pump through the load sensing port"X" (3). The load sensing signal acts with flow