| 摘要 |
PURPOSE:To precisely perform the pressure control by supplying a vent flow rate passing through a relief valve at the time of pressure control from a pump line through a restricting resistance. CONSTITUTION:A spring chamber 16 of a first control valve 11 which makes the discharge quantity control part 6 of a first variable pump 1 communicate selectively with a pump line 2 or a tank 9 to control the discharge quantity is connected with the rear portion of a first check valve 4 of the pump line 2 through a pilot line 17 provided midway with a restricting resistance 19. Since the fluid vented through a relief valve 20 at the time of pressure control is therefore supplied from the pump line 2 through the restricting resistance 19, the fluctuation in a vent flow rate can be prevented at the beginning of the unload operation of a second variable pump 51 after the activation of a directional control valve 72. Thus the pressure fluctuation in the pump line caused by the fluctuation in the vent flow rate can be prevented to precisely perform the pressure control.
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