A stuffing box or gland package is an assembly which is used to house a gland seal. It is used to prevent leakage of fluid, such as water or steam, between sliding or turning parts of machine elements.

Components

A stuffing box of a sailing boat will have a stern tube that is slightly bigger than the prop shaft. It will also have packing nut threads or a gland nut. The packing is inside the gland nut and creates the seal. The shaft is wrapped by the packing and put in the gland nut. Through tightening it onto the stern tube, the packing is compressed, creating a seal against the shaft.Stuffing Box Maintenance
, WindCheck Magazine, Retrieved April 27, 2016. Creating a proper plunger alignment is critical for correct flow and a long wear life. Stuffing box components are of stainless steel, brass or other application-specific materials. Compression packing is rigorously tested to ensure effective sealing in valves, pumps, agitators, and other rotary equipment.

Gland

A gland is a general type of stuffing box, used to seal a rotating or reciprocating shaft against a fluid. The most common example is in the head of a tap ( faucet) where the gland is usually packed with string which has been soaked in

tallow Tallow is a rendered form of beef or mutton fat, primarily made up of triglycerides. In industry, tallow is not strictly defined as beef or mutton fat. In this context, tallow is animal fat that conforms to certain technical criteria, inclu ...

or similar grease. The gland nut allows the packing material to be compressed to form a watertight seal and prevent water leaking up the shaft when the tap is turned on. The gland at the rotating shaft of a

centrifugal pump Centrifugal pumps are used to transport fluids by the conversion of rotational kinetic energy to the hydrodynamic energy of the fluid flow. The rotational energy typically comes from an engine or electric motor. They are a sub-class of dynamic ...

may be packed in a similar way and graphite grease used to accommodate continuous operation. The linear seal around the

piston rod In a piston engine, a piston rod joins a piston to the crosshead and thus to the connecting rod that drives the crankshaft or (for steam locomotives) the driving wheels. Internal combustion engines, and in particular all current automobile engi ...

of a double acting steam piston is also known as a gland, particularly in marine applications. Likewise the shaft of a handpump or wind pump is sealed with a gland where the shaft exits the borehole. Other types of sealed connections without moving parts are also sometimes called glands; for example, a cable gland or fitting that connects a flexible electrical conduit to an enclosure, machine or bulkhead facilitates assembly and prevents liquid or gas ingress.

Applications

Boats

On a boat having an inboard motor that turns a shaft attached to an external

propeller A propeller (colloquially often called a screw if on a ship or an airscrew if on an aircraft) is a device with a rotating hub and radiating blades that are set at a pitch to form a helical spiral which, when rotated, exerts linear thrust upon ...

, the shaft passes through a stuffing box, also called a "packing box" or "stern gland" in this application. The stuffing box prevents water from entering the boat's hull. In many small

fiberglass Fiberglass (American English) or fibreglass (Commonwealth English) is a common type of fiber-reinforced plastic using glass fiber. The fibers may be randomly arranged, flattened into a sheet called a chopped strand mat, or woven into glass cl ...

boats, for example, the stuffing box is mounted inboard near the point the shaft exits the

hull Hull may refer to: Structures * Chassis, of an armored fighting vehicle * Fuselage, of an aircraft * Hull (botany), the outer covering of seeds * Hull (watercraft), the body or frame of a ship * Submarine hull Mathematics * Affine hull, in affi ...

. The "box" is a cylindrical assembly, typically of bronze, comprising a sleeve threaded on one end to accept adjusting and locking nuts. A special purpose heavy-duty rubber hose attaches the stuffing box to a stern tube, also called a shaft log, that projects inward from the hull. Marine-duty hose clamps secure the hose to the stern tube and the aft portion of the stuffing box sleeve. A sound stuffing box installation is critical to safety because failure can admit a catastrophic volume of water into the boat. In a common type of stuffing box, rings of braided fiber, known as shaft packing or gland packing, form a seal between the shaft and the stuffing box. A traditional variety of shaft packing comprises a square cross-section rope made of

flax Flax, also known as common flax or linseed, is a flowering plant, ''Linum usitatissimum'', in the family Linaceae. It is cultivated as a food and fiber crop in regions of the world with temperate climates. Textiles made from flax are known i ...

or hemp impregnated with wax and lubricants. A turn of the adjusting nut compresses the shaft packing. Ideally, the compression is just enough to make the seal both watertight when the shaft is stationary and drip slightly when the shaft is turning. The drip rate must be at once sufficient to lubricate and cool the shaft and packing, but not so much as could sink an unattended boat. There are improved shaft packing materials that aim to be drip-less when the shaft is turning as well as when stationary, also pack-less sealing systems that employ engineered materials such as carbon composites and

PTFE Polytetrafluoroethylene (PTFE) is a synthetic fluoropolymer of tetrafluoroethylene that has numerous applications. It is one of the best-known and widely applied PFAS. The commonly known brand name of PTFE-based composition is Teflon by Chem ...

(e.g. Teflon).

Steam engines

In a

steam engine A steam engine is a heat engine that performs mechanical work using steam as its working fluid. The steam engine uses the force produced by steam pressure to push a piston back and forth inside a cylinder. This pushing force can be ...

, where the piston rod reciprocates through the cylinder cover, a stuffing box provided in the cylinder cover prevents the leakage of steam from the cylinder.

References

External links

Servicing Your Stuffing Box, by Don Casey

Step-by-Step Instructions For Servicing Your Stuffing Box, by Capt. Vincent Daniello, August 16, 2012
{{Steam engine configurations Pistons Marine propulsion Seals (mechanical) Steam engines Piston engines