| 摘要 |
PROBLEM TO BE SOLVED: To provide an operation change-over control circuit which controls a backup selector valve for a plurality of attachments retrofitted in an excavator, according to a pilot pressure system, and correctly controls the retrofitted attachments by a single operating lever without increasing the number of the operating levers, in spite of increased relationships between the operating levers and the selector valve due to employment of the pilot pressure system. SOLUTION: According to the operation change-over control circuit, a main control valve for the actuators retrofitted in the excavator is controlled according to the pilot pressure system, and the selector valve is interposed between the main control valve and the retrofitted actuators. The selector valve is controlled by a solenoid valve, whereby pressure oil fed from the main control valve is fed to the retrofitted actuators by switching connection to the actuators.
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