What prevents the plunger from leaving the hydraulic jack assembly?

The stop ring is the component that prevents the plunger from leaving the hydraulic jack assembly. Its primary function is to provide a physical barrier that stops the plunger's movement once it has extended to its maximum point. By serving as a limit stop, the stop ring ensures that the plunger does not exit the assembly during operation, which is critical for both the safety and functionality of the hydraulic jack.

The use of a stop ring is essential in maintaining the integrity of the hydraulic system, as it helps to avoid any potential damage that could occur if the plunger were to be forced out of its intended path. This confinement of the plunger allows for controlled lifting and lowering operations, which are fundamental to the hydraulic jack’s purpose.

In comparison, while parts like guide bearings, stuffing boxes, and seals play important roles in supporting, containing, or preventing leakage of hydraulic fluid, they do not specifically serve to stop the plunger from exiting the assembly. Their functions are related more to the operational smoothness and efficiency of the hydraulic system rather than directly limiting the plunger's travel.