Hi ddoorroo

Common Courtesy: Hello, Hi, Good Day, Thank You, Sincerely, Best Regards is not mandatory, however most people in this forum still value this courtesy. Especially when ones required a good explanation.

I cannot answer number of rings since this is design driven, related to packing material used and service condition. However below is the background

Gland packing material and temperature limitation
Expanded graphite(max. 450⁰C) ;
Woven carbon fibres(max. 450⁰C);
Woven PTFE (Teflon)(max. 250⁰C);
O-rings (Viton – Kalrez) (150⁰ - 250⁰C);
Woven Aramid fibres (max. 150⁰C)

There are seating stress factor, depending on the composition provided by the manufacturer. Which tells you the composition of packing delivered (for instance industrial standard for Graphite is 97% graphite + 3% PTFE, etc). different "patented" composition will have different seating stress. Applying axial force result in exceeding seating stress will damage the packing or causing the valve stuck.




The K factor is always less than 1
This means:
K = Fax / Frad < 1
best practice note
For graphite rings: maximum approx. 0.6
For woven packing maximum approx. 0.4

Why is this?
This is due to the fact that packing does not have a homogenous structure and does not behave like a liquid.
The power exerted on the gland bolts is not transferred entirely as surface pressure onto the spindle, but is always lower. And therefore the greater the distance from the gland, the lower the sealing surface pressure of the packing on the shaft
It is therefore pointless to add more packing.

Answering your simple question, the number of rings is vary then. You can design it for 10 rings, but shall installed conventionally e.g. put the 10 rings at one go and only tightened it one time through the gland after all 10 ring is inside, then the other let say first 5 Ring would not be beneficial.
Same thing with fewer ring, if only 2 rings installed. it is doable however ones will not have a backup ring and also more prone shall vibration occurs (less fixated) and when operator messing around with the hand-wheel.

I would be really careful in saying this but normally 4 to 5 rings is sufficient with composition of (from bottom to top) anti extrusion ring, braided graphite, pre-compressed graphite/braided 2 or 3 rings and braided graphite.
What is vary between the each size and class is normally the thickness, width and sometimes tolerance between the OD/ID packing vs spindle and packing room.

Regards,
MR





https://nosuchvalve.com
All valves will last for years, except the ones that were poorly manufactured; are still wrongly operated and or were wrongly selected

http://www.eng-tips.com/faqs.cfm?&rat1=2&f...

ddoorroo'
You need to do some work on your own before you Give-up and ask questions on this or any other forum.
1. Look at the Valve and determine the Maker of the Valve
2. Check the Files at the site to determine if there is any literature that addresses spare parts and maintenance. If none found.
3. Go no the internet and find the manufacturers website and Contact information
4. By phone or e-mail ask them for answers the your questions

Sometimes its possible to do all the right things and still get bad results