Working mechanism of a hydraulic jack :-
1-When the handle is pressed down, valve A is closed whereas valve B is opened. The hydraulic fluid is forced into the large cylinder and hence pushes the piston moving upward.
2-When the handle is raised, valve B will be closed while vale A will be opened. Hydraulic fluid from the buffer tank will be suck into the small cylinder.
3-This process is repeated until the load is sufficiently lifted up.
4-The large piston can be lowered down by releasing the hydraulic fluid back to the buffer tank through the release vale.