Patent ID: 6042085
Filing Date: 2000-03-28
Classification: B66F

Abstract:
A jack comprising:a base member (10) having a first chamber (11) defined therein, a first piston (110) movably received in said first chamber (11) and pivotally connected to a lever (20) which is pivotally connected to said base member (10);a main cylinder (30) connected to said base member (20) and having a lifting piston (21) movably received therein which has a passage (210) defined centrally therein, said lifting piston (21) having a piston ring (211) mounted thereto which is movable along the inside of said main cylinder (30), a tube (22) extending from said base member (20) and inserted into said passage (210);a collar (300) mounted to said lifting piston (21) and a casing (31) connected between said collar (300) and said base member (10) so as to define a second chamber (310) between said main cylinder (30) and said casing (31);a first path connecting said second chamber (310) and said first chamber (11), a second path (41) connecting said first chamber (11) and said passage (210), a third path (42) connecting said second chamber (310) and the interior of said main cylinder (30), a first check valve (400) received in said first path (40) to normally close said first path (40) in the direction from said first chamber (11) to said second chamber (310), a second check valve (410) received in said second path (41) to normally close said second path (41) in the direction from said tube (22) to said first chamber (11), a third check valve (420) received in said third path (42) to normally close said third path (42) in the direction from the interior of said main cylinder (30) to said second chamber (310);a protection path extending through said base member (10) and connecting to said second path (41) and having a first section (50), a second section (51) and a third section (52), a fourth check valve (510) received in said second section (51) to normally close said first section (50) in the direction from said second section (51) to said first section (50), a fifth check valve (520) received in said third section to normally close said second section (51) in the direction from said third section (52) to said second section (51);a first branch path (60) connecting the interior of said main cylinder (30) and said second section (51), a second branch path (61) connecting said third section (52) and said second chamber (310), anda bolt (70) threadedly engaged with said third section (52) and engaged with said fifth check valve (520).