Since these back-up stem seals rotate against the TFE bushings, valve shell leakage, indicating wear on the outside of these seals, is virtually unreported.

• 由于这些阀杆密封支撑靠着TFE衬套旋转，所以显示这些密封外部磨损导致的阀门外壳泄漏实际上就没有再发生。