Patent ID: 6892535

Claim:
In a hydraulic circuit for a boom cylinder combining operation which includes a plurality of hydraulic pumps, a boom cylinder connected with a hydraulic pump, a boom cylinder combining spool which is installed in a flow path between the hydraulic pump and the boom cylinder for combining the operation oil from the hydraulic pumps in a switching mode, a boom cylinder driving spool which is installed in a flow path between the hydraulic pump and the boom cylinder and controls a driving, stop and direction change of the boom cylinder in a switching mode, and a remote control, valve which supplies a pilot signal pressure to the boom cylinder combining spool and the boom cylinder driving spool, said boom cylinder combining spool, comprising: a first inner path which is formed in one side of the boom cylinder combining spool and connects a hydraulic pump and a boom cylinder large chamber in a switching mode; a second inner path which is formed in the other side of the boom cylinder combining spool and connects an operation oil from the hydraulic pump to a hydraulic tank in a switching mode; and a third inner path which is formed in the other side of the boom cylinder combining spool and combines the operation oils from the small chamber and large chamber of the boom cylinder in a switching mode and connects the same to the hydraulic tank.