BUCKET AS 4765194 - Caterpillar

Illustration 1 g00928457
Secondary Steering Pump (1) Large pump section (2) Small pump section (3) Outlet to steering control valve (4) Plug (5) Plug (6) Spring (7) Seat (8) Passage to pump outlet (9) Passage (10) Inlet from tank (11) Valve spool (12) Passage (13) Check valve (14) PassageThe secondary steering pump operates only when the machine is moving forward. When the machine moves, the pump gears that are in small pump section (2) and large pump section (1) create a low pressure area. The pressure in the pressurized hydraulic tank forces oil into the low pressure area. Oil flows into steering pump inlet (10) .Oil from small pump section (2) passes through outlet (3) to the steering control valve.Output oil from large pump section (1) is controlled by valve spool (11). When sufficient engine RPM is maintained, pilot oil from the steering pump enters through passage (14). Pilot oil pressure overcomes the force of spring (6). The valve spool moves toward passage (9). This causes oil from the large pump section to flow around the valve spool. Then, the oil flows through passage (12) back to the inlet side of the large pump section. This means that only oil from small pump section (2) flows to the steering control valve.When the machine is moving and the engine RPM decreases below a sufficient speed or the engine stops, the pilot oil from the steering pump will decrease. The force of spring (6) overcomes pilot oil pressure. Valve spool (11) moves away from passage (9). Oil from large pump section (1) is directed through check valve (13) and passage (8) to the pump outlet. The output oil of both the large pump section and small pump section (2) then flow through outlet (3) to the steering control valve.If the machine moves backward, the secondary steering pump will not send oil to the steering control valve. When the machine moves backward and the main steering pump fails, the machine cannot be steered.