A stuffing box is a type of seal that prevents fluids from leaking inside of machine parts. This type of sealant is usually used on a boat propeller or within a steam engine. When water, steam, and other fluids infiltrate a boat's propeller or a steam engine, the result can be disastrous, which is why a stuffing box is necessary.
When used within a nautical setting, a stuffing box is wrapped around the shaft of a boat's propeller. Since most boats have propellers that are submerged under water, liquid could easily cause a propeller to malfunction if a stuffing box were not present. The material inside of this seal is made from small rings that have been greased with flax oil. Once these rings have been tightly wrapped around the propeller shaft, a nut and spacer are used to secure the rope to the shaft.
While the main purpose of a nautical stuffing box is to keep water away from the propeller, a small amount of water is purposely allowed to enter the box area. The percentage of water that is permitted to seep into the box is not enough to harm a boat's propeller, though it is enough to provide sufficient lubrication for the box. Flax rings are useful, though non-drip seals made from Teflon or carbon are also highly efficient.
Likewise, stuffing boxes can also be used to seal a steam engine. In the case of a steam engine, it is placed strategically within the piston area. The main purpose of a steam engine box is to prevent cylinder steam from leaking into the engine. Since steam engines produce a large amount of steam, this type of prevention would be impossible without a proper sealant. Were steam allowed to penetrate the engine area, the engine may cease to function. As with a nautical box, a steam engine stuffing box allows an engine to function without risk of water or steam damage.
These protective sealants can be purchased by contacting a specialized manufacturer or by searching the Internet. However, stuffing boxes are generally built into any seaworthy ship or steam engine, though these sealants may need to be replaced over time. Installation of these sealants can be difficult without the help of a mechanical professional.