A REVIEW OF VALVE STEM SEALING TO PREVENT LEAKAGE

Stem sealing plays an important role in valve operation, to avoid leakage from the valve. 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 materials, Teflon (PTFE), graphite or graphoil like vitons can be used to 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 H2S containing fluid, displaying a low friction factor to the stem, providing very good sealing capability to prevent leakage from the valve stem area. 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 but removing rings can also increase the risk of leakage from the valve. Keywords: Valve sealing, torque, valve stem friction.