ENGINE AR 1953816 - Caterpillar

Illustration 1 g03724987
(1) Return line (2) Return passage (3) Return line (4) Makeup line (5) Slow return check valve (6) Hydraulic oil cooler (7) Bypass check valve (8) Negative flow control orifice (9) Center bypass passage (10) Return passage (11) Main control valve (12) Center bypass passage (13) Negative flow control orifice (14) Travel motors (15) Case drain line (16) Swing motor (17) Case drain line (18) Case drain line (19) Return filter (20) Hydraulic tank (21) Case drain filter (22) Case drain line (23) Suction line (24) Idler pump (25) Drive pump (26) Pilot pumpThe oil delivery from drive pump (25) and idler pump (24) enters main control valve (11). The oil then flows to return passage (2) and return line (1) 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 drive pump (25) flows through center bypass passage (12) and negative flow control orifice (13) to return line (3). Pump low pressure standby oil from idler pump (24) flows through center bypass passage (9) and negative flow control orifice (8) to return line (1) .
When any one of the joysticks and/or travel levers/pedals is shifted from the NEUTRAL position, center bypass passages (12) and (9) are blocked. The return oil from the cylinders and/or motors now flows through return passage (10) to return line (1) .
The return oil from return line (3) and return line (1) flows through slow return check valve (5) .
Case drain oil from drive pump (25) and idler pump (24) flows into case drain line (22). Case drain oil from swing motor (16) and travel motors (14) flows into respective case drain lines (17) and (15). The case drain oil from the motors flows through case drain line (18) and combines with the case drain oil from the pumps at case drain line (22). All of the case drain oil from the pumps and the motors now flows through case drain filter (21) to hydraulic tank (20) .
Makeup line (4) will route return oil to the inlet port of swing motor (16) if a vacuum condition occurs at swing motor (16) during swing stop.
When the oil temperature is very low, most of the oil is returned through bypass check valve (7) to hydraulic tank (20). The remainder of the oil flows into oil cooler (6) and return filter (19) to hydraulic tank (20) .
When the oil temperature increases, the rate of oil flow through bypass check valve (7) decreases. This causes the rate of oil flow through oil cooler (6) to increase.ReferenceFor 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:
Systems Operation, "Check Valve (Return Makeup)"
Systems Operation, "Oil Makeup (Swing System)"
Systems Operation, "Relief Valve (Swing)"