Low profile jack construction.

摘要

A mechanical jack construction is provided comprising a load-bearing rack (24, 28) which is adapted to be moved in the vertical plane by an engaging pinion (32). The pinion is connected to a lever-driven ratchet wheel (50) by means of shear pins (46). Application of an excessive load to the load-bearing rack will result in fracture of the shear pins, disengagement of the pinion from the ratchet wheel and substantially instantaneous lowering of the rack. Such construction lends itself to use in track repair and similar applications in which immediate jack retraction is desired upon engagement of excessive loads.