Hydraulic anti-theft device

In an earth-working machine including a tractor and implement attachment, said tractor having rear ground-engaging wheels, and a stabilizer arm assembly for stabilizing the tractor on the ground when the implement attachment is in an operative position, and stabilizing arm assembly including a hydraulic piston-cylinder actuator which is extensible to raise the rear tractor wheels off the ground such that the tractor and implement may not be moved, the improvement comprising:

• a locking device mounted to said extensible hydraulic actuator, said locking device including an assembly of flow control valves which are selectively movable between an open flow position permitting extension and retraction of said hydraulic actuator and a locked position to prevent hydraulic fluid from leaving the hydraulic actuator when it is extended for raising the tractor wheels off the ground, thereby rendering the machine immovable;
• said locking device including a valve body having a series of longitudinally aligned housings for mounting said flow control valves, said valve body including an inlet port connecting a fluid pressure supply line to one of said housings and an oulet port connecting another housing to said hydraulic actuator, said housings being interconnected by a transverse flow passage to permit fluid flow through said body from the inlet port to the outlet port when said control valves are moved to their open flow position;
• said locking device including an inlet flow control valve, an outlet flow control valve, and at least one intermediate flow control valve, said inlet and outlet control valves each including a core having an L-shaped flow passage transverse to the longitudinal axis of the core for connecting either the inlet or outlet ports to the transverse flow passage through said valve body, each intermediate flow control valve including a core with a flow passage, said flow passage being selectively aligned with the flow passage through the valve body to permit fluid flow through the body from the inlet port to the outlet port when the inlet and outlet control valves are positioned for open flow;
• said control valves including rotatable indicator knobs at one of their ends for setting the open flow and locked positions of the valves, each knob including indicia which is selectively aligned with the ends of the flow passages through the control valves to provide the operator with a means of selectively setting the valves to an open flow or locked position, and said valve knobs being adjustable such that the operator may periodically change the combination for the locking device;
• and
• said knobs including removable cover means for hiding the combination used to unlock the device when the machine is in operation.