KIT-REPAIR 2427123 - Caterpillar

Hydraulic Schematic for Return Circuit
Illustration 1 g00668865
(1) Swing motor (2) Travel motors (3) Drain line (4) Drain line (5) Makeup line (6) Oil cooler (9) Passage (10) Bypass check valve (11) Center bypass valve (12) Center bypass valve (13) Main control valve (14) Slow return check valve (15) Drain line (16) Orifice (17) Orifice (18) Return passage (19) Hydraulic tank (20) Right pump (21) Suction line (22) Left pumpIntroduction
The oil from right pump (20) and left pump (22) enters return passage (18) in main control valve (13) in the following manner:
Under no load conditions, right pump oil flows through center bypass passage (11) and orifice (17) to return passage (18). Left pump oil flows through center bypass passage (12) and orifice (16) to return passage (18) .
Under load conditions, return oil from each control valve for travel, swing, and implements goes to return passage (18) .Oil in return passage (18) goes to slow return check valve (14) and flows to hydraulic tank (19) after separating in the following manner:
When the oil temperature is very low, most of the return oil goes through bypass check valve (10) and back to hydraulic tank (19). A small amount of the oil goes through oil cooler (6) to hydraulic tank (19) .
As the oil temperature increases, the rate of oil flow through bypass check valve (10) decreases and the rate of oil flow through oil cooler (6) increases.Case drain oil from swing motor (1) goes through drain line (3). Case drain oil from travel motors (2) goes through drain line (4). Case drain oil from the motors combines at drain line (15). The oil then enters hydraulic tank (19) .If a vacuum occurs in the swing motor, makeup line (5) directs part of the oil to the motor. The makeup oil eliminates the vacuum condition.Slow Return Check Valve and Oil Cooler
Illustration 2 g00668289
Control valve compartment (10) Bypass check valve (13) Control valve (14) Slow return check valve (23) Inlet line to oil cooler (24) Return line
Illustration 3 g00668307
Left side of engine (bottom view) (6) Oil cooler (7) Return line (23) Inlet line to oil cooler (25) Outlet line from oil cooler to hydraulic tankSlow return check valve (14) is located between control valve (13) and oil cooler (6). The slow return check valve restricts the oil flow in return passage (18). This resistance maintains a constant pressure in the return line. This allows part of the oil in makeup line (5) to go to the swing motor in order to remove the vacuum condition.Note: For more information on the makeup operation, refer to System Operation, "Piston Motor (Swing)".Return oil flow from slow return check valve (14) passes through passage (9). Passage (9) sends the oil flow to inlet line (23) and to bypass check valve (10). Inlet line (23) sends the oil flow to oil cooler (6). The oil cooler is bolted to the engine radiator. The oil is cooled in the oil cooler. The oil is returned to hydraulic tank (19) through outlet line (25) .