Leakage from valve stem packing and gaskets directly affects the safe operation of industrial plants and environmental compliance. As an authorized distributor of SUFA, Akameng has long served valve selection and maintenance in the power, chemical, and water industries. Drawing on field engineering experience, this article outlines how to assess leakage from stem packing and gaskets and the key points for controlling it.
Internal Leakage vs. External Leakage: Two Distinct Hazards
Valve leakage is generally classified into two categories: internal leakage and external leakage. Internal leakage refers to medium still passing through the sealing surfaces after the valve is closed, directly compromising the shut-off function and potentially causing medium waste, process disruption, or even safety accidents. External leakage refers to medium escaping into the surrounding environment through the stem packing, flange gaskets, and other joints—causing resource loss and serving as a major source of fugitive emissions of volatile organic compounds (VOCs).
Visible Leakage and Fugitive Leakage
In industrial practice, leakage assessment involves two levels: "visible" and "fugitive." Visible leakage can be identified by the naked eye, such as medium seeping out, dripping, or forming bubbles at the stem or flange joints. In factory hydrostatic or pneumatic tests, the industry-standard "zero leakage" criterion is based on visible leakage, and SUFA's factory inspection strictly follows this standard.
Fugitive leakage, on the other hand, is a minute leakage invisible to the naked eye, detectable only with high-sensitivity instruments. It mainly occurs in two areas: the dynamic seal of the stem packing and the static seal of the gasket. Gaskets, as static seals, can relatively easily meet low-leakage requirements when correctly installed and operated. Stem packing, however, is a dynamic seal: the reciprocating or rotary motion of the stem continuously rubs against the packing, causing wear, particle carryover, and fluctuating sealing force. This makes packing the most challenging point in fugitive emission control and a key focus of SUFA's valve R&D efforts.
Three Keys to Reducing Leakage
Based on field experience, controlling leakage from stem packing and gaskets typically involves three aspects. First, selection: choose matching packing materials and gasket types according to the medium, temperature, and pressure class—flexible graphite and metal-wound gaskets are recommended for high-temperature, high-pressure conditions. Second, installation: strictly control the pre-tightening force of the packing gland; overtightening can jam the stem while undertightening causes leakage, and flange gaskets must be centered and evenly tightened according to specifications. Third, maintenance: regularly inspect packing wear and adjust the compression promptly, replacing packing when necessary to keep the valve well sealed over its service life.
Leakage control is an important part of whole-life-cycle valve management. If you encounter sealing problems in valve selection, installation, or maintenance, please contact Akameng—our technical team can provide targeted advice based on your actual operating conditions. To learn about SUFA's full range of valve products, browse our Product Center or call 15851489497.