| 摘要 |
PROBLEM TO BE SOLVED: To simultaneously drive a turning motor and a boom cylinder even if delivery of a variable delivery pump reduces by a load of the turning motor when simultaneously starting the turning motor and the boom cylinder in a power shovel having a horse power constant control function. SOLUTION: A pair of stoppers 4, 5 for controlling the switching stroke are arranged in a turning motor controlling pilot directional control valve 1. Control cylinders 6, 7 are arranged to regulate switching quantity of the pilot directional control valve 1 by striking on these stoppers. While, a timer valve 9 is provided to supply a pressure fluid to the control cylinders or to check the supply. The timer valve 9 is constituted so as to introduce common pilot pressure to both side pilot chambers by arranging the pilot chambers 9b, 9c on both sides, the pilot pressure is directly introduced to one pilot chamber, a spring 12 is arranged in the other pilot chamber, the pilot pressure is introduced via a timing control orifice 10, and this other pilot chamber is communicated with a tank T via a pressure holding orifice 11.
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