What is valve stem packing?
Valve stem packing is the process of tightening the valve gland follower with packing material to reduce or eliminate process leaks. It is important for the performance of the process and also for safety, regulatory compliance
Types of valve packing:
There are mainly two types of valve packing, Chevron valve packing and Rope or Ring type packing
Chevron valve packing:
The material used for chevron rings are Teflon or rubber. Teflon or rubber packing rings are shaped like a V and placed in the stuffing box.
The process pressure forces the edges of the chevrons outwards against the shaft and stuffing box wall to produce a good seal. Chevron packing is very common in hydraulic and pneumatic systems.
Rope type packing:
Rope type packing comes in various styles. The most common materials used to make these ropes are Teflon/Asbestos or graphited asbestos.
Valve packing Procedure:
We have to repack the valve if we cannot control the leakage by adjusting the gland follower. The first step of repacking is removing the old pack and then cleaning the gland and then installing the new pack.
Removing the pack:
- Open the gland follower dog bolts & open the gland follower
- Remove the packing rings using packing tools, without scratching the shaft
- If there is a lantern ring, remove this with a piece of wire bent into a hook.
- Make sure all packing scraps have been removed.
Installing New Packing:
- Clean the shaft well using a non-flammable, non-toxic solvent.
- Brush down and then wipe the area with a clean rag
- Calculate how many rings will be required by measuring the gap between the shaft and the stuffing box, the depth of the stuffing box and the thickness of the lantern ring
- Wind the packing material round the mandrel as many times as the number of rings required.
- Cut the rings with a sharp knife.
- Check how many rings you need to put below the lantern ring. Only correct number of rings can place below the lantern ring. Otherwise, it will not be in line with the lubricator.
- Lubricate the rings with an anti-seize compound, so they will go in more easily
- Insert the packing rings and lantern ring one by one, pushing them into the stuffing box as far as they can go
- Ring joints should stagger and cut on a slant, as shown: