(57) The jack comprises a base (1) having a rack (1c), an inverted U-section load lifting
arm (5) slidable horizontally on a pivot pin (12) in guide channels (1a) of the base
(1), a strut (6) pivoted to the lifting arm (5) and to the base (1), a jacking arm
(4) pivoted on the pin (12) and carrying a jacking pawl (2) which co-operates with
the rack (1c) to lift the load in steps and a locking pawl (3) which transfers the
load on the lifting arm (5) to the rack (1c) between the stepwise jacking movements.
During load lowering, the pawls (2,3) are alternately raised by a spring (9) and during
load raising the action of spring (9) is overcome and both pawls (2, 3) are biased
into engagement with the rack (1c) by a raising spring (8). Preferably, a slider (30)
automatically pivots the spring (8) to an inoperative position when the jack is fully
raised and into an operative position when the jack is fully lowered.
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