Structural characteristics of pressure balanced plug valve and treatment methods for internal leakage

Most of the imported Serck Audco pressure balanced plug valves are adopted for the bypass throttle valves, vent valves and station ESD vent valves of the block valve on the trunk line of PetroChina West-to-East Gas Pipeline. Internal leakage faults of plug valves for station ESD high-pressure venting occur frequently, but the conventional treatment appears not to be satisfactory. Through the analysis on structural characteristics of sealing and pressure balance of the imported plug valves, treatment methods such as grease filling, disassembly for maintenance, valve replacement, and return for repair were put forward based on field practical experience. The root causes of frequent internal leakage of plug valve attribute to abrasion and scratch on surface of plug valve body that may result in sealing failure. During field disassembly and maintenance, the clearance between the plug and the valve body was hard to be restored to its original state. It is hardly possible to reach the original fit accuracy after manual grinding, and the repair effect may be worse after several times of disassembly. So the disassembly and maintenance should be treated with caution. Return for repair might be able to eliminate the abrasion and scratch on the plug surface, and the internal leakage problem of the valve was verified by the site test and proved to be solvable. But for domestic plug valves or imported plug valves repaired by domestic manufacturers, the additional pressure relief nozzle at the large end of the plug is required to eliminate the plug self-locking phenomenon. The pressure relief nozzle at the large end is in direct contact with the medium fluid, and impurities cannot be prevented from entering the bottom of the large end under the working condition that the valve is used for pipeline medium containing large amounts of impurities. Research should be carried out in these aspects for the localization development of plug valves.