Abstract: A retractable leg structure for undecking a crane's upper from its carrier including a box member having a circular cross section and a longitudinal axis affixed to the upper, a beam retained within the box and rotatable about the longitudinal axis relative thereto, and an L-shaped leg, including a tubular member having a free end hinged to the beam, the leg being manually swingable about the hinged connection between a stowed position in which the tubular member is oriented horizontal and inboard of the upper and a deployed position in which the tubular member is horizontal and outboard of the upper. There is a lock pin device for selectively securing the leg in one of the deployed and stowed positions, and an extendable jack secured to the fee end of the tubular member along with a crank arm attached to the beam. A hydraulic ram connected to the crank arm moves the leg between the deployed position and an operative position wherein the tubular member is oriented vertically adjacent to the ground.

Abstract: A centering device for aligning those portions of the swing mechanism, e.g. the swing pinion on the upper with the ring gear on the carrier, to permit the redecking of a crane upper on its carrier, the device including a plurality of sockets on the carrier which are engageable by frustoconical ends on a plurality of pins slidably mounted on the upper. A latch holds the pins in an extended position so that the retraction of the legs supporting the upper above the carrier will cause lateral shifting as necessary to align the swing mechanism.

Abstract: An improved anti-two block system having a boom hoist drum driven by a first hydraulic motor with a first variable displacement motor controlled by a first ram moveable in a given direction to supply fluid pressure for driving the boom drum to lower a boom and a hook block drum driven by a second hydraulic motor with a second variable displacement pump controlled by second ram moveable in a given direction to supply fluid pressure for driving the hook drum to raise a hook block. A differential mechanism sums the movement of the hook block and boom and activates a switch to energize solenoid valve means, when the hook block is a predetermined distance from the boom, to preclude movement of said rams in the given directions.