Lift for agricultural implement

Claim 1

IN AN IMPLEMENT ATTACHMENT FOR A TRACTOR HAVING A SOURCE OF FLUID UNDER PRESSURE, A TOOL-CARRYING FRAME HAVING MEANS THEREON FOR CONNECTION TO THE TRACTOR IN DRAFTRECEIVING RELATION, A PAIR OF CRANK AXLES HAVING LONGITUDINALLY SPACED PARALLEL AXLE SECTIOSN ROCKABLY MOUNTED ON THE FRAME AND WHEEL-CARRYING ARM SECTIONS ON OPPOSITE SIDES OF THE FRAME, SAID ARM SECTIONS BEING SWINGABLE UPON ROCKING AND AXLE SECTIONS RELATIVE TO THE FRAME TO RAISE AND LOWER THE LATTER, A ROCKABLE MEMBER AFFIXED TO EACH AXLE SECTION, A ONE-WAY HYDRAULIC POWER UNIT EXTENDING BETWEEN SAID ROCKABLE MEMBERS INCLUDING A CYLINDER PIVOTALLY CONNECTED TO ONE OF SAID ROCKABLE MEMBERS AND A PISTON ROD PIVOTALLY CONNECTED TO THE OTHER, SAID ROD BEING EXTENDIBLE UNDER PRESSURE OF FLUID RECEIVED FROM SAID SOURCE TO ROCK SAID ROCKABLE MEMBERS IN OPPOSITE DIRECTIONS TO RAISE THE FRAME AND RECTRACTABLE UPON RELEASE OF THE PRESSURE ON THE FLUID TO LOWER THE FRAME AND STOP MEANS ON THE FRAME ENGAGEABLE WITH SAID ROCKABLE MEMBERS AFTER A PREDETERMINED RETRACTION OF SAID PISTON ROD TO LIMIT THE EXTENT TO WHICH THE FRAME CAN BE LOWERED.