What does the packing in a valve prevent?

The packing in a valve is specifically designed to create a seal around the stem of the valve, preventing the passage of the fluid or gas contained within the valve from leaking out. In the context of steam systems, this is particularly critical, as steam operates at high temperatures and pressures. If steam were to leak from a valve, it could lead to not only energy loss but also blowback and potential safety hazards.

The packing material compresses against the valve stem as it is tightened, which effectively blocks the high-pressure steam from escaping. This functionality is vital in maintaining the integrity of the system and ensuring efficient operation, as well as protecting personnel from exposure to hot steam. While packing may help with other types of leaks, such as air, water, or fuel, its primary and most critical application often focuses on preventing steam leaks, especially in high-pressure environments.