BOOM CYLINDER CONTROL CIRCUIT FOR CONSTRUCTION MACHINE

摘要

The present invention relates to a boom cylinder control circuit for a construction machine, comprising: a boom cylinder which includes an ascending-side chamber and a descending-side chamber; a boom control unit which provides the boom cylinder with working fluid; a boom operation part which provides the boom control unit with pilot working fluid to operate the boom operation part to drive the boom cylinder; a first floating valve which selectively connects or disconnects each of the ascending-side chamber and descending-side chamber with a first drain line; a second floating valve which is additionally provided in a flow path between the descending-side chamber connected with the first drain line via the first floating valve and the first drain line to either connect the descending-side chamber with the first drain line, or to disconnect the discharge of working fluid from the descending-side chamber to the first drain line and to enable backward flowing; and a floating selection operation part (10) which provides an operation signal to switch the first floating valve and second floating valve in a connection or disconnection direction.