Hydraulic circuit system for use in hydraulically operated vehicles

Claim 1

A hydraulic circuit system for use in hydraulically operated vehicles, comprising: (a) a forwardly and reversely rotatable slewing motor having a brake unit associated therewith and hydraulic fluid circuits for rotating said slewing motor forwardly and reversely; (b) a directional control valve for connecting and disconnecting said fluid circuits with and from a pressurized fluid supply source, said control valve having an OFF position and forward and reverse rotating positions and being remotely controlled by a pilot fluid pressure; (c) bypass circuits, one ends of which are respectively connected to said fluid circuits; (d) a shadow valve having a communicating position for allowing said bypass circuits to communicate with each other at their respective other ends and disconnecting positions for disconnecting said bypass circuits from each other, said shadow valve being interlocked with said directional control valve to enable interlocked control to be achieved in such a manner that it may assume its communicating position when said directional control valve is located at its OFF position, while it may assume its disconnecting positions when said directional control valve is located at either forward or reverse rotating position, and (e) an ON-OFF changeover valve provided in said bypass circuits for allowing said bypass circuits to communicate with and disconnect from said shadow valve.