| 摘要 |
During manual operation, pilot pressure discharged from a pilot pump (41) is fed from a manual operation valve (44a) or (44b) through an electromagnetic change valve (49a) or (49b) to a main control val ve (33). During automatic operation, pilot pressure whic h is output from an automatic-mode selecting valve (46) is fed through an electro magnetic proportional control valve (48a) or (48b) as we ll as an electromagnetic change valve (49a) or (49b), all of which are controlled by a controller (21), to main control valve (33). When limiting the operation range of the attachment during manual operation, pilot pressur e output from manual operation valve (44a) or (44b) is f ed through electromagnetic proportional control valve (48a) or (48b) as well as electromagnetic change valve (49a) or (49b) to main con trol valve (33). At that time, main control valve (33) is returned to the neutra l position by causing electromagnetic proportional contr ol valve (48a) or (48b), which are both controlled by control signals from controller (21), to block the pilot pressure.
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