PURPOSE: To reduce a shock by gradually increasing the valve opening pressure of a check valve according to an external signal when pump delivery pressure is supplied from valve blocks on both sides to plurality of actuators.
CONSTITUTION: When a boom cylinder and a turning motor are simultaneously operated, pilot pressure oil is supplied from a pilot pipe line 116 to a check valve 118, and valve opening pressure is therefore gradually increased in proportion to the force of the pilot pressure oil. Since the delivery pressure of a hydraulic pump 20 is not supplied to the port 42 of a valve block 30-2 on the other side from a passage 119, and the load pressure of the turning motor is therefore not detected from the third port 43 to a load pressure detecting path 82, the pressure compensating valve of a valve block 30-1 is set by the load pressure of a boom cylinder, and boom ascending speed does not lower. In addition, when pressure in a passage 117 exceeds the valve opening pressure of the check valve 118, since the pressure in the passage 117 flows into the second port 42 to gradually increase the load pressure, and a flow rate into the boom cylinder changes smoothly to check the occurrence of a shock.
AKASHI MITSUMASA
AKIYAMA TERUO
