Cranes

Claim 1

A crane including a generally vertical boom which comprises at least three sections, namely first, second and third sections, telescopically associated for relative movement between contracted and extended condition, and in the extended condition of which the first section is the uppermost of the three sections and the third said section is the lowermost, an extension cable operatively interconnected between the respective said sections for extending same in response to tensioning of the cable, latch mechanism carried by each of the first and second of said sections for lateral movement into and from locking engagement with an adjacent said section to interlock said sections in their extended relationship, a portion of said extension cable extending in a generally vertical path, a latch release bar guided for generally horizontal movement on each of said first and second sections and linked to the latch mechanism of the respective sections for releasing said mechanism, responsive to horizontal movement of the respective bars; spring means resiliently urging said respective bars horizontally toward operative positions to engage the latch mechanisms, each said release bar extending transversely to said cable portion of its respective section and having means thereon for engaging and laterally deflecting said portion of the extension cable when the release bar is in said operative position under the influence of its spring means, each said release bar being retractable horizontally to a position for releasing its associated latch mechanism responsive to the application of tension to said extension cable in an amount sufficient to overcome the latch engaging pressure exerted thereon by its spring, each said latch mechanism of the uppermost section, when in locking engagement with said second section, supporting the uppermost section on said second section and being normally maintained in locking engagement by the weight of the uppermost section, the tensioning of said extension cable sufficiently to raise the uppermost said section to permit release of its said latch mechanism, being insufficient to raise said second section with the first section.