Hydraulic jack and a hydraulic circuit for such a hydraulic jack

A hydraulic circuit for a continuously auto lifting and lowering hydraulic jack, comprising an oil pump;

• a working oil cylinder, a piston, an oil box, an accumulator, a two-position and two-way valve, a dual-controlling check valve, a pressure-set check valve and a plurality of further check valves, said hydraulic circuit further including:
• a first oil line, in which a lower chamber of said working oil cylinder communicates fluidly with said oil box through said two-position and two-way valve;
• a second oil line, in which said oil box communicates fluidly with the lower chamber of said working oil cylinder through a first check valve of said plurality of further check valves;
• a third oil line, in which said oil box communicates fluidly with said dual-controlling check valve through successively one of the checks, said oil pump and a third check valve of said plurality of further check values;
• a fourth oil line in which an upper chamber of said working oil cylinder communicates fluidly with said oil box through said pressure-set check valve and said accumulator;
• and
• said two-position and two-way valve, said dual-controlling check valve and said pressure-set check are connected sequentially and fluidly in series, wherein said dual-controlling check valve is disposed between said first oil line and said fourth line to fluid communicate said two oil lines.