GB944997A - Improvements in or relating to lifting jacks - Google Patents

Abstract

944,997. Ratchet lifting jacks. BLACKSTONE & CO. Ltd. March 22, 1962 [March 23, 1961], No. 10721/61. Heading B8J. In a racket-lifting jack in which a pawl 21, pivoted to a lever 17, and a holding pawl 28, pivoted to the frame 11, 15, engage a rack 12, the pawls are interconnected to prevent them both from disengaging from the rack at the same time during the lifting operation. As shown, the pawl 21 is pivoted on a pin 20 on the lever 17 and is provided with a tail 24 which is connected by a spring 25 to a lug 26 on the lever 17. A link 33, pivoted at 34 to the frame 15, is provided with a slot 41 and a camshaped opening 35 engaging, respectively, a pin 42 on the pawl 21 and a pin 36 on an interlock lever 37 pivoted at 32 to the frame 15. The lever 37 has a cam face 38 which engages a roller 39 on the holding pawl 28. If pawl 21 is lifted out of engagement with the rack teeth 23, the pin 42 moves the lever 33 to the right and causes the lever 37 to be turned to bring its tail 43 into engagement with the pawl 28, thereby holding it positively in engagement with the rack teeth. To lower the rack, a rod 48, slidably mounted on the lever 17, is pressed inwardly to the position 48a thereby moving one arm of a spring 50 into engagement with a head 51 on the lever 37 and causing the cam face 38 to engage roller 39 to move the pawl 28 out of engagement with the rack. The other arm of the spring 50 engages a roller 56 on the tail of a driving pawl 57 and when the rod 48 is in the position 48a, the spring 50 overcomes the spring 58 and causes the pawl 57 to hook over the rack tooth 23, so that when the lever 15 is raised to lower the rack, the pawl 57 ensures that the rack is pushed downwards. Specification 721,616 is referred to.