Valvestem

Valvestem, commonly written as valve stem, is the component of a valve that transmits motion from the actuator or handle to the valve’s internal element (such as a disc, plug, or gate), thereby opening or closing the valve. The stem passes through the bonnet and is sealed with packing glands or O-rings to prevent leakage along the stem.

Stems come in rising and non-rising configurations. In rising-stem designs, the stem moves upward as the valve opens, making travel visible and allowing packing adjustment at the bonnet. In non-rising stems, the stem remains stationary while the internal element moves; these are used where space is constrained or where stem travel must be minimized. Stems are typically metal, often stainless or carbon steel, brass, or bronze, and may be threaded, square-ended, or splined to interface with handwheels, gear operators, or actuators. They are attached to the valve disc, plug, or gate, and to the operating mechanism, sometimes via a yoke or bonnet.

Sealing and wear: the stem is a primary source of leakage when packing deteriorates; proper packing selection and adjustment are essential. Stems may suffer wear or galling at threads or contact surfaces; surfaces are often ground and, in corrosive environments, treated or coated.

Maintenance: routine inspection for bending, corrosion, and packing leakage; replace packing and, if needed, the stem, to restore operation.

Applications: widely used in water systems, chemical processing, oil and gas, and power plants.

See also: Valve, Globe valve, Gate valve, Ball valve.