Komatsu WA120-3, WA120-3CS Wheel Loader Repair Manual

Serial Numbers:
50001 and up, 10004 and up(WA120-3)
10004 and up(WA120-3CS)
Manuals: Shop Manual
General
Structure and Functions
Testing and Adjusting
Disassembly and Assembly
Maintenance Standard
Others
Manual Extract Main Control Valve:
Outline
The main control valve is a control valve which controls the operation of the bucket and attachments in the hydraulic system. It is a tandem circuit for the bucket priority circuit.
The oil from the pump enters port F and the maximum pressure is set by the relief valve.

The oil passes through the bypass circuits of bucket spool (2) and boom spool (1 ), flows from port E to the drain circuit, then passes through the filter and returns to the tank. If the bucket and boom spools are actuated, the oil flows to the bucket and boom cylinders.

However, a bucket priority circuit is used, so when the bucket spool is operated, the boom is not actuated even if the boom spool is operated.

Two safety valves (with suction) (4) are installed to protect the circuit if abnormal pressure is generated in the bucket circuit. The two safety valves have two functions: acting as relief valves and acting as suction valves to compensate for lack of oil.