HYDRAULIC CONTROL CIRCUIT OF BOOM CYLINDER OF WORKING MACHINE

摘要

A hydraulic control circuit of a boom cylinder (8) capable of improving a fuel consumption, increasing a working efficiency in combined operation, and increasing the workability and operability of the works requiring a difficult boom operation such as rubble scraping operation and top soil placing operation when pressure oil is controllably supplied to and discharged from the boom cylinder, comprising a first selector valve (19) for holding a boom control valve (13) at a neutral position (N), a communication oil path (E) for communicating a head side oil chamber (8a) with a rod side oil chamber (8b), a stop valve (18) for opening and closing the communication oil path, and a pilot operated check valve (20) switchable between a one-way mode for allowing an oil flow from the head side oil chamber to the rod side oil chamber but stopping an oil flow in reverse direction and a two-way mode for allowing an oil flow in both directions.