BREAKAGE PREVENTION DEVICE OF BOOM WORKING MACHINE

摘要

PROBLEM TO BE SOLVED: To prevent an A frame from being damaged when a boom is derricked. SOLUTION: The A frame 10 for supporting a derricking rope 5a is mounted on a swing body 2. The A frame 10 can be elevated between a transport attitude and a working attitude by the telescoping of a derricking cylinder 13. When the transport attitude of the A frame 10 is detected by the attitude detector 61, a solenoid selector valve 54 is changed over to a position port by control signals from a controller 60. Thus the supply of pressure oil from a hydraulic pump 51 is stopped to prohibit the driving of a derricking drum 5.