Crowell & Moring LLP
Hydraulic system for work machine
When option attachment has not been attached, a reserve flow/direction control valve 8 is made to operate as a center bypass cut valve. When an option attachment has been attached, switching control is performed. In the switching control, when the option attachment is not used, the reserve flow/direction control valve 8 is made to operate as a center bypass cut valve for adjusting composite opening area of a center bypass and thereby controlling the flow rate of hydraulic fluid flowing into an actuator. When the option attachment is used, the reserve flow/direction control valve 8 is made to operate so as to supply the hydraulic fluid to an option hydraulic actuator 14. 
Hitachi Construction Machinery Co., Ltd
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Tomoaki Hidetoshi Kouji Shinya
Kaneta Satake Ishikawa Imura