GB1385884A - Load raising and lowering jacking apparatus - Google Patents

Abstract

1385884 Step-by-step jacks B BARBACK and H G PRIMROSE 19 Dec 1972 [30 Sept 1971] 45463/71 Heading B8J A step-by-step jack comprises upper and lower crossheads 10, 11 interconnected by hydraulic jacks 12, 12a. A vertical rack 15 is pivotally suspended at 17 from a support 18 and extends through the crossheads 10, 11. A load (not shown) to be raised or lowered is supported by a trunnion 19 carried by the upper crosshead 10. Supporting pawls 22, 22a are pivoted on the upper crosshead 10 at 21, 21a and are biased into contact with teeth 16 on the rack 15 by weights 24 on levers 23, 23a also pivoted at 21, 21a and having interengaging teeth 26. Operating pawls 29, 29a are similarly mounted on the lower crosshead 11. Auxiliary cylinders 33, 33a are mounted on the upper crosshead 10 to co-operate with the pawls 22, 22a and 29, 29a respectively. When the auxiliary cylinders 33, 33a are unpressurized extension and retraction of rams 14, 14a of the jacks 12, 12a raises the load step-by-step the load being taken alternately by the pawls 22, 22a and 29, 29a, the unloaded pawls ratcheting over the teeth 16. To lower a load the auxiliary cylinders 33, 33a are pressurized, but the pressure supplied is too low to disengage the pawls 22, 22a and 29, 29a except when the load is carried by the other set of pawls. In the position shown this means that the pawls 22, 22a remain engaged while the pawls 29,29a are pivoted out of engagement with the teeth 16. The jacks 12, 12a are now extended and the crosshead 11 moves downwardly. This moves actuating pin 36a on the lever 30a out of contact with head 35a on ram 34a of auxiliary cylinder 33a allowing the weights 31 to bias the pawls 29, 29a back into contact with the teeth 16 of the rack 15. Continued extension of the jacks 12, 12a transfers the load from the pawls 22, 22a to the pawls 29, 29a allowing the auxiliary cylinder 33 to disengage the pawls 22, 22a by means of its ram 34 acting on pin 36 on the lever 24 through its head 35. Retraction of the jacks 12, 12a now lowers the crosshead 10, with attached load. This brings a push rod 35b on the crosshead 11 into contact with the pin 36 which forces the ram 34 back into the auxiliary cylinder 33 and allows the pawls 22, 22a to re-engage the teeth 16. Continued retraction of the jacks 12, 12a transfers the load to the pawls 22, 22a when the apparatus is ready for another cycle. In a modification, Fig. 2 (not shown), lower crosshead (42) is supported on beams (44) and a load attached to a rack (45) is raised and lowered by raising and lowering the rack (45).