Stem lip seals.

The lipseal are being widely used b almost all the valve manufactures in the stem sealing. Some ball valve manufactures have developed the trend of offering extended bonnet in ball valves due to the use of such sealing to move the sealing element away from the body to have reduced temp. exposure. Another reason for the extended bonnet is usage of the PTFE materials in the bushing. These solutions give better efficient sealing in stems. But the stem size gets changed and other counter piping arrangement problem occurs. However alternative graphite packing with fillers are new combinations and still available in market. Engineers evaluating the valves should take note of the these materials to avoid the inconvenience for piping layout engineering and in the aesthetics of the plant in overall.