| 摘要 |
PROBLEM TO BE SOLVED: To prevent a rapid decrease in pump discharge flow by providing a first pilot chamber for directly leading load side pressure to a timer valve of a second pilot line and a second pilot chamber for leading load side pressure via a restriction. SOLUTION: A timer valve TV normally keeps a release position (a) by spring force of a spring 25. Staring pressure directly acts on a pilot chamber 22 by starting of a revolving motor and the valve TV is switched to a restriction position (b). But when starting pressure acts on also a pressure chamber 23a, a piston 24 is moved, spring 25 is bent, spring force is gradually increased and a pressure action of the pilot chamber 22 is overcome, the valve TV is returned to the release position (a). Returning time is determined by pressure receiving area of the piston 24, spring force of the spring 25 and opening of the restriction 34. Thus, because the valve TV is switched to the restriction position (b), timing for rising of pilot pressure in a second pilot line 15a is delayed, also load pressure of the revolving motor becomes low for the time and decrease of pump delivery can be prevented.
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