Patent ID: 7155908

Claim:
In a hydraulic system for a heavy equipment with option apparatus, the hydraulic system including a plurality of hydraulic pumps a first control valve (C 1 ) for controlling an operation oil supplied from a first hydraulic pump (P 1 ) to a right side traveling motor and a second control valve (C 2 ) for controlling an operation oil from a second hydraulic pump (P 2 ), and a pilot pump which supplies a pilot signal pressure to the control valves respectively, the improvements comprising: a straight traveling control valve (C 4 ) which controls operation oil supplies from a third hydraulic pump (P 3 ) by a pilot signal pressure (Pi 3 ), and disconnects the operation oil supply of the third hydraulic pump (P 3 ) by another pilot signal pressure (Pi 1 ), and an inner spool having a flowing path communicated with the first, second and third hydraulic pump (P 1 , P 2 and P 3 ); and an option apparatus control valve (C 5 ) which is switched concurrently with the straight traveling control valve (C 4 ) by the pilot signal pressure (Pi 3 ) and controls an operation oil supplied from the third hydraulic pump P 3 to the option apparatus.