A Review of Valve Stem Sealing to Prevent Leakage from the Valve and Its Effect on Valve Operation

Abstract

Stem sealing plays an important role in valve operation, to avoid leakage from the valve stem area to the environment. Additionally, accuracy and tight sealing of stem seals are vital in fugitive emission applications where hazardous fluids such as gases or vapours may escape if a valve is not sealed properly. Soft thermoplastic and elastomer materials such as Teflon (PTFE), lip seal, V-pack, Viton as well as graphite or graphoil can be used for valve stem sealing. Appropriate stem sealing or packing depends on the process conditions where the valve will be used, including being able to withstand extreme temperatures, being resistant to aggressive fluid such as ${\text{H}}_{2}$S containing fluid, displaying a low friction factor to the stem, providing very good sealing capability to prevent leakage from the valve stem area, and being adequately strong and economical. The sealing capability of compression packing is defined as the ability to expand laterally against the stem and stuffing box wall when stressed by tightening the gland. The stem sealing arrangement depends on the type of valves being used and the applications. The sealing capability and performance of a valve can be validated by testing the valve stem sealing through mechanical and temperature cycles based on different American Petroleum Institute standards or by finite element analysis. The torque required to operate a valve depends on parameters such as the packing or stem sealing material, number of stem sealing rings, load of gland flange, stem surface finish, temperature, and cycling. Reducing the number of packing rings can reduce the valve torque and the actuator sizing but removing rings can also increase the risk of leakage from the valve and reduce the effectiveness of the valve seals.