| 摘要 |
PROBLEM TO BE SOLVED: To impart a shockless function without receiving the action of back pressure at hydraulic motor driving time by connecting respective secondary pressure chambers of one relief valve and the other relief valve to a valve device in which a ball type moving body is installed. SOLUTION: When normally rotating a hydraulic motor 4 by communicating a main passage 5 with a hydraulic pump l and a main passage 6 with an oil tank 2, high pressure oil of the passage 5 acts on a check valve 34 from a passage 35 via a secondary pressure chamber 26 of a relief valve 14, so that back pressure of the passage 6 acts on a passage 36. Since pressure of the passage 35 is higher than the passage 36, a ball 34a of the check valve 34 is pressed to the passage 36 side so as to be kept in a normal start position. When returning a directional control valve 3 to neutral, the passages 5, 6 are cut off, the hydraulic motor 4 takes the pump action by inertia, passage 6 side pressure increases, pressure oil strokes the ball 34a to the left side through an orifice 25, and during that time, preset pressure of a secondary pressure chamber 27 of a relief valve 15 is maintained low to thereby reliably absorb a shock of the hydraulic motor.
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