A valve stem packing is used to provide tight support to prevent leakage of the process fluid.
The hole in the bonnet is quite a bit larger in diameter than step's diameter. so, that extra space we have to fill from preventing a leak of the process by using valve packing.
This is Teflon rings shown in the below figure is designed such a way that it fits in each other properly.
Not all the packing are used as live loaded packing. Some others come with solid arrangement instead of spring.
Step to remove the valve packing :
1. Open packing flange by removing bolt then remove packing follower.
2. Remove packing rings using packing tool like scriber, without damaging shaft.
3. Remove other items like spring, if live loaded packing and if not then remove solid part available with packing ring.
Step to install new valve packing :
1. Clen the shaft and plug using non-flammable, non-toxic solvent or use IPA solution.
2. Remove all the dirt using a rag.
3. If there is a lantern ring also used with packing then calculate how many rings are used before and after packing rings or count ring which you have removed.
4. Lubricate ring using lubrication comes with the set.
5. Put packing ring one by one on the stem, If there is live loaded packing is used then insert first, spring then packing ring.
6. A ring should fit properly as shown in the above figure.