The stem is an important part of driving the opening and closing part to open and close the valve because the stem is a movable part. So it's easy to leak. Therefore, the hard seal closing rod is very important for the valve. The hard sealing closed rod can compress the structure of the packing: because of the characteristics of asbestos, most compression fillers use asbestos fiber as the base material. It is basically not affected by most media, temperature and time, and is a good heat conductor. The disadvantage of asbestos is its poor lubricity, so lubricants that do not affect the properties of asbestos, such as graphite powder and mica powder, must be added.

Since the mixture is still permeable, a liquid lubricant must be added. PTFE has the characteristics of small shrinkage, low shrinkage and low friction coefficient. It has high corrosion resistance to most corrosive media. The working temperature of polytetrafluoroethylene filler is-150 ~ 260 ℃. In this temperature range, it is a high-performance multi-function stem packing. Flexible graphite has the property of high temperature resistance. It also has a small coefficient of friction and can resist most corrosive media. The working temperature of the filler can reach 600 °C. Therefore, flexible graphite packing is used for high temperature valves in power stations, petrochemical and other departments.