Hyraulic jack

A hydraulic jack, comprising a piston cylinder (1), a piston rod (2), an oil passage switching valve (3) and an internal cylinder (4);

• the piston rod (2) is disposed inside the piston cylinder (1) and performs up and down movement in the piston cylinder (1);
• a piston cylinder oil storage chamber (11) is formed between the piston rod (2) and the piston cylinder (1);
• the oil passage switching valve (3) is disposed at a lower end of the piston cylinder (1);
• the internal cylinder (4) is sleeved outside the piston cylinder (1) and an internal cylinder oil storage chamber (41) is formed between the internal cylinder (4) and the piston cylinder (1);
• a piston oil inlet passage (12) communicating the piston cylinder oil storage chamber (11) and the internal cylinder oil storage chamber (41) is disposed on the piston cylinder (1), wherein the oil passage switching valve (3) is provided with a piston cylinder mounting groove (31);
• a lower end of the piston cylinder (1) is mounted in the piston cylinder mounting groove (31);
• a first oil inlet passage (32) is disposed at a groove bottom of the piston cylinder mounting groove (31);
• the oil passage switching valve (3) is provided with an oil outlet passage (33) in communication with the first oil inlet passage (32), and a one-way valve assembly (5) for preventing the backflow of the oil outlet passage (33) is disposed between the first oil inlet passage (32) and the oil outlet passage (33);
• a lower end of the piston rod (2) is connected with a piston head (21) for opening or closing the first oil inlet passage (32);
• a return oil inlet passage (22) is disposed at the bottom of the piston head (21);
• a return oil chamber (23) in communication with the return oil inlet passage (22) is disposed inside the piston head (21);
• a return oil outlet passage (24) communicating the return oil chamber (23) and the piston cylinder oil storage chamber (11) is disposed on the piston head (21);
• a one-way return oil assembly (6) is mounted between the return oil inlet passage (22) and the return oil outlet passage (24) in the return oil chamber (23);
• the one-way return oil assembly (6) is used to prevent the return oil outlet passage (24) from flowing back to the return oil inlet passage (22).