SEAL 5E8905 - Caterpillar

Upper Return Hydraulic System
Illustration 1 g03383138
(1) Engine fan (2) Swivel (3) Lower shutoff valve (4) Cab manual lowering valves (5) Cab up/down (6) Cab for/aft (7) Grapple (8) Stick hydraulic cylinders (9) Boom hydraulic cylinders (10) Hydraulic lockout (11) Main upper control valve (12) Pump (13) Swing control valve (14) Hydraulic oil cooler fan motor (15) Hydraulic oil cooler (16) Rear back pressure manifolds (17) Front back pressure manifolds (18) Swing pump (19) Swing motor (20) Swing cooling shuttle valve (21) Hydraulic cooler fan pump (22) Return Filters (23) Swing system case drain (24) Main pumps case drain (25) Lower motor case drain (26) Hydraulic tankLower Return Hydraulic System
Illustration 2 g03383191
(27) Travel motor (28) Shift piston (29) Counter balance valve (30) Parking brake (31) Main lower control valve (32) Warming manifold (optional) (33) Swivel (34) Oscillating axle lockThe oil delivery from the pumps enters main control valve. The oil then flows to the return line and the return passage 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 the pump flows through center bypass passage and the negative flow control orifice to the return passage. Pump low pressure standby oil from the pump flows through the center bypass passage and negative flow control orifice to the return passage .When any one of the joysticks and/or travel levers/pedals is shifted from the NEUTRAL position, center bypass passages are blocked. The return oil from the cylinders and/or motors now flows through the return passages to the return line.The return oil from the return passages flows through the slow return check valve and the return line .When the oil temperature is low, most of the oil is returned through the bypass check valve to the hydraulic tank. The remainder of the oil flows into the oil cooler and return filter to the hydraulic tank.When the oil temperature increases, the rate of oil flow through the bypass check valve decreases. This action causes the rate of oil flow through the oil cooler to increase.ReferenceFor more information concerning the bypass check valve, refer to Systems Operation, "Bypass Valve (Return)".Case drain oil from the pumps flows into the case drain line. Case drain oil then flows from line to case drain filter and into hydraulic tank. Case drain oil from swing motor and travel motors flows into respective case drain lines. The case drain oil then combines and flows through the case drain line. The case drain oil from case drain line then flows through case drain filter and into the hydraulic tank.Makeup line will route return oil to the inlet port of the swing motor if a vacuum condition occurs at the swing motor 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)"
Systems Operation, "Oil Makeup (Swing System)"
Systems Operation, "Relief Valve (Swing)"