Both hydraulic jacks and screw jacks have a self-locking function, which means that when the handle is stopped from being pressed, the plunger can still maintain its current position and not be affected by pressure to descend. The self-locking function of screw jacks relies on the deviation angle and friction force of the threads. So, what is the self-locking function of hydraulic jacks?

In the self-locking principle of hydraulic jacks, there is a special structure commonly known as the "locking mechanism" or "self-locking valve". Its function is to prevent liquid from flowing back when the jack reaches the desired height, thereby maintaining the position of the jack and even if the pressure of the hydraulic system is released, it can maintain the height of the load.

The function of this locking mechanism is similar to a valve, which opens when the jack is lifted, allowing liquid to enter the cylinder, but closes when the jack stops lifting and pressurization, preventing liquid from returning to the hydraulic system, thus maintaining the position of the jack. This self-locking mechanism ensures that the jack can firmly maintain the required height.