324D Excavator Hydraulic System Caterpillar

Return Hydraulic System

Usage:

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Illustration 1	g01178547
(1) Swing motor (2) Travel motors (3) Case drain line (4) Case drain line (5) Makeup line (makeup oil to swing motor) (6) Return line (7) Return passage (8) Return line (9) Return passage (10) Main control valve (11) Center bypass passage (12) Negative flow control orifice (13) Negative flow control orifice (14) Case drain line (15) Center bypass passage (16) Return line (17) Slow return check valve (18) Hydraulic oil cooler (19) Return filter (20) Left pump (21) Right pump (22) Pilot pump (23) Case drain filter (24) Bypass check valve (25) Hydraulic tank (26) Case drain line (27) Suction line

The oil delivery from right pump (21) and left pump (20) enters main control valve (10). The oil then flows to return passage (7) and return line (6) in one of the following manners:

When all joysticks and/or travel levers/pedals are in the NEUTRAL position, pump low pressure standby oil from right pump (21) flows through center bypass passage (11) and negative flow control orifice (12) to return line (6). Pump low pressure standby oil from left pump (20) flows through center bypass passage (15) and negative flow control orifice (13) to return line (8) .
When any one of the joysticks and/or travel levers/pedals is shifted from the NEUTRAL position, center bypass passages (11) and (15) are blocked. The return oil from the cylinders and/or motors now flows through return passage (9) to return line (8) .
The return oil from return line (6) and return line (8) flows through return line (16) and slow return check valve (17) .
Case drain oil from right pump (21) and left pump (20) flows into case drain line (26). Case drain oil from swing motor (1) and travel motors (2) flows into respective case drain lines (3) and (4). The case drain oil from the motors flows through case drain line (14) and combines with the case drain oil from the pumps at case drain line (26). All of the case drain oil from the pumps and the motors now flows through case drain filter (23) to hydraulic tank (25) .
Makeup line (5) will route return oil to the inlet port of the swing motor if a vacuum condition occurs at the swing motor during swing stop.
When the oil temperature is very low, most of the oil is returned through bypass check valve (24) to hydraulic tank (25). The remainder of the oil flows into oil cooler (18) and return filter (19) to hydraulic tank (25) .
When the oil temperature increases, the rate of oil flow through bypass check valve (24) decreases. This causes the rate of oil flow through oil cooler (18) to increase.

Reference: For more information concerning the bypass check valve, refer to Systems Operation, "Bypass Valve (Return)".

For more information concerning the makeup operation of the return hydraulic system at the swing motor, refer to the following sections in this manual: