TUBE 3434382 - Caterpillar

Return System Overview
Illustration 1 g03848142
Return system schematic
(1) Swing motor
(2) Right travel motor
(3) Case drain line
(4) Case drain line
(5) Left travel motor
(6) Case drain line
(7) Swivel
(8) Make up line
(9) Main control valve
(10) Main Pump
(11) Pump delivery line
(12) Suction line
(13) Return passage
(14) Relief valve (hydraulic oil filter)
(15) Hydraulic tank
(16) Hydraulic oil filter
(17) Bypass check valve
(18) Return line
(19) Valve
(20) Return line
(21) Hydraulic oil cooler
(22) Return line
(23) Case drain line
Illustration 2 g03816530
System for the hydraulic oil return
(9) Main control valve
(15) Hydraulic tank
(17) Bypass check valve
(18) Return line
(20) Return line
(21) Hydraulic oil cooler
(22) Return line
(24) Filler cap
(25) Access plate (suction filter)
(26) Access plate (oil filter)
(27) Case drain manifold block The oil from main pump (10) enters main control valve (9). Then, the oil flows to the return passages in one of the following conditions.
When all joysticks and/or travel levers/pedals are in the NEUTRAL position, oil from the main pump flows into the main control valve (9). Pressure in the passage increases and the oil shifts valve (19). Oil then flows through return passage (13) to the return lines.
When any one of the joysticks and/or travel levers/pedals shift from NEUTRAL position, the return oil from the cylinders and/or motors now flows to return passage (13) and to the return lines.The return oil from return passage (13) flows through bypass check valve (17) back to hydraulic tank (15) in one of the following conditions.
When the oil temperature is low, most of the oil is returned through bypass check valve (17) to hydraulic tank (15). The remainder of the oil flows into oil cooler (21) to hydraulic tank (15).
When the oil temperature increases, the rate of oil flow through bypass check valve (17) decreases. This action causes the rate of oil flow through oil cooler (21) to increase.Case drain oil from swing motor (1) and travel motors (2) and (5) flows into respective drain lines (3), (4), and (6). The case drain oil combines in line (23) and flows into hydraulic tank (15).Makeup line (8) will route return oil to the inlet port of the swing motor if a vacuum condition occurs at the swing motor during swing stop.Hydraulic Oil Cooler
Illustration 3 g03816548
Hydraulic Oil Cooler
(21) Oil Cooler
(28) Outlet
(29) Inlet The hydraulic oil cooler (21) is mounted in front of the engine on the right side of the engine coolant radiator. The hydraulic oil flows through the hydraulic oil cooler in order to maintain the operating temperature of the oil. A fan that is driven by the engine pulls air through the cooler. At operating temperature, return oil from the main control valve flows through the slow return check valve through the return line and inlet (29) to hydraulic oil cooler (21). The hydraulic oil that is cooled and flows through outlet (28). The oil then flows through the return line to the return filter in the hydraulic tank.Hydraulic Tank and Filter
Illustration 4 g03816552
Components of the hydraulic tank
(17) Bypass check valve
(24) Filler cap
(25) Access plate (suction filter)
(26) Access plate (oil filter)
(30) Fluid level sight
(31) Suction filter
(32) Oil filter
(33) Relief valve
(34) Return