Automatic boom control

Claim 1

IN COMBINATION WITH A TRACTOR, A LONGITUDINALLY EXTENDING BOOM PIVOTED AT ITS REAR END ON SAID TRACTOR VERTICAL SWINGING MOVEMENT ABOUT A TRANSVERSE PIVOT AXIS, A MATERIAL HANDLING ATTACHMENT SECURED TO THE FRONT END OF SAID BOOM, A FLUID MOTOR INTERCONNECTED BETWEEN SAID TRACTOR AND BOOM FOR MOVING THE LATTER ABOUT SAID TRANSVERSE PIVOT AXIS BETWEEN ELEVATED AND LOWERED POSITIONS, A CONTROL VALVE ON SAID TRACTOR FOR SAID MOTOR INCLUDING A SHIFTABLE FLOW CONTROL ELEMENT HAVING SPACED RAISE AND FLOAT POSITIONS, A HOLD POSITION BETWEEN SAID RAISE AND FLOAT POSITION AND A LOWER POSITION BETWEEN SAID HOLD AND FLOAT POSITION, DETENT MEANS FRO RELEASABLY HOLDING SAID ELEMENT IN SAID RAISE AND FLOAT POSITIONS ONLY AND CENTERING MENS OPERATIVE TO MOVE SAID ELEMENT TO SAID HOLD POSITION WHEN MOVED OUT OF SAID DETENTED RAISE AND HOLD POSITION, AND MOTION RESPONSIVE MEANS POSITIONED BETWEEN SAID FLOW CONTROL ELEMENT AND BOOM FOR AUTOMATICALLY MOVING SAID FLOW CONTROL ELEMENT OUT OF ITS DETENTED RAISE AND FLOAT POSITIONS TOWARD SAID HOLD POSITION WHEN SAID BOOM IS MOVED TO PREDETERMINED ELEVATED AND LOWERED POSITIONS, RESPECTIVELY, A SAID CONTROL ELEMENT BEING SHIFTABLE TO SAID LOWER POSITION IMMEDIATELY AFTER ITS BEING AUTOMATICALLY MOVED OUT OF ITS FLOAT POSITION WITHOUT ITS INCURRING INTERFERENCE WITH SAID MOTION RESPONSIVE MEANS.