FAN AS 2956662 - Caterpillar

Illustration 1 g03329140
(1) Travel motor (2) Swing motor (3) Drain line (4) Drain line (5) Makeup line (6) Main control valve (7) Center bypass passage (8) Return passage (9) Main pump (10) Drain line (11) Return line (12) Hydraulic filter (13) Oil cooler (14) Return line (15) Hydraulic tank (16) Parallel feeder passage (17) Passage (18) Passage (19) Passage (20) Return Passage (21) Return line (22) Filter (23) Proportional reducing valve (24) Attachment control valve (25) Hydraulic lockout switch (26) Two-speed travel relay (27) Two-speed travel switchThe oil from main pump (9) enters main control valve (6). Then, the oil flows to the return passages in one of the following conditions. Return oil flow takes one of two paths.
When all joysticks and/or travel levers/pedals are in the NEUTRAL position, oil from main pump (9) flows through center bypass passage (7). Oil then flows through return line (11) to hydraulic tank (15) .
Except for attachment control valve (24), when any one of the joysticks and/or travel levers/pedals shift from NEUTRAL position, oil flow through the center bypass passage (7) is blocked. The return oil from the cylinders and/or motors now flows through return passage (20), return line (11), and back to hydraulic tank (15) .The return oil from return passage (20) and center bypass passage (7) flows through hydraulic filter (12) back to hydraulic tank (15) in one of the following conditions.
When the oil temperature is low, most of the oil is returned through hydraulic filter (12) to hydraulic tank (15). The remainder of the oil flows into oil cooler (13) to hydraulic tank (15) .
When the oil temperature increases, the rate of oil flow through oil cooler (13) from hydraulic filter (12) increases.Case drain oil from main pump (9) flows into case drain line (10). Case drain oil from swing motor (2) and travel motors (1) flows into respective drain lines (3) and (4). Oil flow from drain lines (3) and (4) flows to hydraulic tank (15) .Makeup line (5) will route return oil to the inlet port of swing motor (2) if a vacuum condition occurs during swing stop.For more information concerning the makeup operation of the return hydraulic system at the swing motor, refer to the following sections in this manual.
Systems Operation, "Check Valve (Return Makeup) (Slow Return Check Valve)"
Systems Operation, "Oil Makeup (Swing System)"
Systems Operation, "Relief Valve (Swing)"