Patent ID: 7293670
Filing Date: 2007-11-13
Classification: B66C,B66D

Abstract:
1. An overhead crane comprising: a rotatable drum; a lower block; an upper block having a support wall; two wire ropes having ends secured to the upper block and extending from the upper block to the lower block and from the lower block to the upper block so that the lower block is lifted when the drum rotates to wind the wire ropes around the drum and so that the lower block is lowered when the drum rotates to unwind the wire ropes from the drum; a guide frame; wherein the support wall is movably positioned within the guide frame and restricted to only vertical movement within the guide frame; at least one hydraulic cylinder vertically positioned between the guide frame and support wall so that the support wall is supported on the guide frame by the at least one hydraulic cylinder and any load carried by the crane translates into fluid pressure within the at least one hydraulic cylinder; and a pressure relief valve connected to the hydraulic cylinder, the pressure relief valve opening if the fluid in the hydraulic cylinder exceeds a predetermined pressure value to relieve pressure within the hydraulic cylinder and cause the support wall to move down within the guide frame.