PIN, SUPPORT 0930496 - Caterpillar

Hydraulic Schematic for Return Circuit
Illustration 1 g00974790
(1) Swing motor (2) Travel motor (3) Drain line (4) Drain line (5) Makeup line (6) Return passage (7) Main control valve (8) Center bypass passages (9) Orifice (10) Orifice (11) Return line (12) Center bypass passage (13) Cooling pump (14) Drain line (15) Drain filter (16) Slow return check valve (17) Return line (18) Bypass check valve (19) Return filter (20) Upper pump (21) Pilot pump (22) Line (23) Oil cooler (24) Hydraulic tank (25) Cooling pump relief valve (26) Cooling fan motor (27) Pilot line (28) Suction line (29) Lower pump (30) Line (31) Makeup valveIntroduction
The oil from upper pump (20) and lower pump (29) enters the main control valves. The oil then flows to return passage (6) under one of the following conditions:There is no load on the machine.
Upper pump oil flows into center bypass passage (8) and orifice (9) to return passage (6) .
Lower pump oil flows into center bypass passage (12) and orifice (10) to return passage (6) .There is a load on the machine.
Return oil from each control valve for travel, swing, and implements flows to return passage (6) .The oil from return passage (6) flows through return line (11) and slow return check valve (16). The oil then flows to the hydraulic tank in the following manner:
When the oil is at a very low oil temperature, most of the oil is returned through bypass check valve (18) to hydraulic tank (24). The remainder of the oil flows into oil cooler (23) and return filter (19) to hydraulic tank (24) .
When the oil temperature increases, the rate of oil flow through bypass check valve (18) decreases. This causes the rate of oil flow through oil cooler (23) to increase.Case drain oil from swing motor (1) and travel motor (2) flows into respective drain lines (3) and (4), and the oil combines at drain line (14). The oil then returns to hydraulic tank (24) through case drain filter (15) .If a vacuum occurs in the swing motor, makeup line (5) will route oil to the inlet of the motor. Routing oil to the inlet of the motor will eliminate the vacuum condition.This machine uses a separate cooling pump for cooling purposes. The output flow from cooling pump (13) is used to turn cooling fan motor (26). The output flow from cooling pump (13) flows into oil cooler (23). The output flow from cooling pump (13) flows into line (30) to cooling fan motor (26). The output oil drives the fan motor. Cooling fan motor (26) passes air over oil cooler (23), the radiator and the air conditioner condenser. The speed of cooling fan motor (26) is limited by the output flow of cooling pump (13) .Components in Return Circuit
This section describes the construction and operation of the following components of the return circuit:
Oil cooler
Bypass check valve
Return filter and hydraulic tank
Drain filterSlow Return Check Valve and Oil Cooler
Illustration 2 g00291290
Main control valve compartment (return circuit) (5) Makeup line (7) Control