 | |
| Illustration 1 | g01416904 |
Hydraulic schematic for return circuit (1) Stick lowering control valve (2) Boom lowering control valves (3) Right travel motor (4) Left travel motor (5) Right swing motor (6) Left swing motor (7) Line (case drain) (8) Line (case drain) (9) Swing control valve (10) Back pressure valve (11) Main control valve (12) Passage (pump output flow) (13) Passage (pump output flow) (13) Neutral flow control valve (14) Differential pressure relief valve (15) Passage (return oil flow from control valve spools) (16) Differential pressure relief valve (17) Passage (return oil flow from control valve spools) (18) Makeup line (19) Return line (20) Return line (21) Bypass check valve (22) Back pressure valve (23) Return line (24) Case drain filter (25) Return filter (26) Hydraulic oil cooler (27) Case drain filter (28) Line (case drain) (29) Fan motor (30) Line (output flow from cooling pump) (31) Suction line (32) Hydraulic tank (33) Line (case drain) (34) Front pump (35) Rear pump (36) Cooling pump (37) Swing pump | |
Return Oil Flow
At NO-LOAD condition, the oil delivery from the front pump (34), rear pump (35), swing pump (37), and cooling pump (36) returns to the hydraulic tank in the following manner.
- The oil delivery from the front pump and the rear pump flows into passage (12) of main control valve (11). Oil then flows through neutral flow control valve (15). The return oil is then separated into the following two oil paths. Part of the return oil flows through return line (19) and (20) to bypass check valve (21). The remainder of the return oil flows through return line (23), back pressure valve (22) and oil cooler (26). The return oil then flows through the return filters (25) into hydraulic tank (32) .
- The oil delivery from swing pump (37) flows through swing control valve (9), through back pressure valve (10) and into return line (19). The return oil is then separated into the following two oil paths. Part of the return oil flows from return line (19) to bypass check valve (21). The remainder of the return oil flows through return lines (20) and (23), back pressure valve (22) and oil cooler (26). The return oil then flows through the return filters (25) into hydraulic tank (32) .
At LOAD condition, return oil from the cylinders and motors returns to the hydraulic tank in the following manner.
- Return oil from the travel motors and the implement cylinders enters main control valve (11). Return oil from the travel control valve and the implement control valves in the main control valve flows into passages (15) and (17). The return oil then flows into return lines (20), (19) and (23). The return oil in return line (23) flows through back pressure valve (22). The return oil in return lines (20) and (19) flows through bypass check valve (21). All of the return oil flows through return filters (25) into hydraulic tank (32) .
- Return oil from the swing motors flows through swing control valve (9) and back pressure valve (10). The return oil then flows into return lines (20), (19) and (23). The return oil in return line (23) flows through back pressure valve (22). The return oil in return lines (20) and (19) flows through bypass check valve (21). All of the return oil flows through return filters (25) into hydraulic tank (32) .
Regardless of the presence of load, when the return oil is at a low temperature, most of the return oil flows through bypass check valve (21) into hydraulic tank (32). As the oil temperature increases, the amount of return oil flow through bypass check valve (21) decreases. The amount of return oil that flows from back pressure valve (22) to hydraulic oil cooler (26) increases.
At UNLOAD condition, the oil delivery from front pump (34) and rear pump (35) returns to the hydraulic tank in the following manner.
- When the load is released, the oil delivery from the front pump and the rear pump flows into passage (12) and into passage (13) rapidly. When the oil pressure from the front pump and the rear pump is 2940 kPa (430 psi) higher than the true load signal pressure of the motors and implements, pump delivery pressure acts on differential pressure relief valve (16) and differential pressure relief valve (14). The differential pressure relief valves open. The oil delivery from the front pump and the rear pump flows into passage (15) and passage (17) into the hydraulic tank.
The case drain oil for the pumps and the motors flows in the following manner.
- Case drain oil from front pump (34), rear pump (35) and swing pump (37) flows through line (33) to case drain filter (24). The oil then flows to hydraulic tank (32) .
- The case drain oil from right travel motor (3), left travel motor (4), right swing motor (5), left swing motor (6), and cooling fan motor (29) and cooling pump (36) flows into drain filter (27). The oil then flows to hydraulic tank (32) .
Back pressure valve (10) restricts the return oil from the swing motors in order to prevent a vacuum condition in the motors. The pressure in return lines (20) and (23) increases due to bypass check valve (21) and back pressure valve (22). If a vacuum condition occurs in the swing motors, the oil in return lines (20) and (23) is delivered to the motors through makeup line (18) in order to release the vacuum.
The hydraulic oil cooling system and the engine cooling system for this machine type are different from the systems for other machine types. The cooling fan is not driven through the engine. The cooling fan is driven by an exclusively equipped fan motor (29). The oil delivery of cooling pump (36) flows through line (30) to the cooling fan motor (29). The fan is driven by the cooling fan motor in order to cool the hydraulic oil cooler, the radiator and the condenser for the air conditioner. The rotational speed of fan motor (29) is limited by the flow of cooling pump (36) .