×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Contact US

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Globe Valve PTFE Gland Packing Failure

Globe Valve PTFE Gland Packing Failure

Globe Valve PTFE Gland Packing Failure

(OP)
Dear All,

We are using plug globe valves as isolating valves on our ammonia circulation pumps. Temperature of service varies between zero degree C to ambient temperature of 25 degree C. We have recently been observing leakages from these valves glands. The valves were installed about 30 years ago and progressively there service life has reduced from 4-5 years in service to 2-3 years now. As recommended by OEM 30 years ago we are still using chevron style Plain PTFE material packing rings on the valve. During every refurbishment we observe the packing rings to be very hard. PTFE obviously gets hard while in service and I am trying to get to the bottom of why these packing rings get hard even though we are operating in standard operating range for PTFE.

Is it because PTFE material is inherently a bad conductor and hence friction induced heat does not dissipate easily and hardens the packing? If so feedback from experts here would be greatly appreciated to improve my understanding of the situation and actual phenomena that is occuring.

If the experts here feel there may be another reason for this kindly share your feedback as well.

We are also cognizant of the fact PTFE with fillers are now available in the market now that are there precisely to cover for plain PTFE's deficiencies. Graphite or Graphite filled PTFE packing rings is expected to provide improved result?

Regards,

RE: Globe Valve PTFE Gland Packing Failure

Leakage is more likely because the metal parts have developed abrasions and the abrasions are cutting the PTFE allowing it to leak.

Polish the metal interfaces and see if that helps.

All I can think of for hardness is that some material is being absorbed into the PTFE. The PTFE molecules are extraordinarily tough; the Fluorine atoms are well bonded to the carbon core. All I see for hardening is high density x-ray exposure.

Alternatively, one aspect of specifying PTFE is the %crystal content. It's possible that this has changed, though I don't see how that would cause a hardness change over time with the temperatures you are using.

Most fillers are to increase the hardness of PTFE, which is normally extremely low. A person's fingernail can damage a PTFE surface.

RE: Globe Valve PTFE Gland Packing Failure

What are" plug globe valves"?

A glove valve moves up and down, a plug valve rotates a plug within the valve.

If your shaft is only rotating then that is one issue but vertical up and down is another. Which is it?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Globe Valve PTFE Gland Packing Failure


Looking at the chemistry PTFE or PCTFE (Polytetrafluorethylen and the somewaht mechanical stronger Polychlortrifluorethylen) are the best sealing material for ammonium based fluids.

It could (but not very likely) happen that the materials you now buy differ slightly in production process and composition from the original and therefore will give a shorter lifetime.

I believe the reason to be other, and also believe that other material compositions/additions will not improve the standing time.

The most common causes for increased sealing leakage over time is dirt, corrosion, wear giving unprecise movement or all in combination. This kind of leakages will not be stopped by renewing sealings, the imprecision in movement, hairline scratches rougher surfaces causing leakage will still be there.

(This is often case in spite of properly maintained and 'cleaned' production pipes.)

Earlier hardening of sealings (presumed material composition exactly equal as original) might well come from earlier starting leakages giving gas exposure to larger areas of the now more roughened up sealing material.

Good luck, it will be interesting to hear your further conclusions!

RE: Globe Valve PTFE Gland Packing Failure

A bit confused in regards to the plug globe valve as well. Need additional clarification before I can provide my input.

RE: Globe Valve PTFE Gland Packing Failure

Your old packing will tell you the answer you seek. However, i will say 3 years is definitely acceptable life for them.

a couple hint, look to see differences between top and bottom rings. can email me if need additional help.

chevron ptfe style packing have one of the lowest torques and widest compatibility, and works perfect for rotating stems.

Luke | Valve Hax | https://valvehax.com/

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login


Resources

Low-Volume Rapid Injection Molding With 3D Printed Molds
Learn methods and guidelines for using stereolithography (SLA) 3D printed molds in the injection molding process to lower costs and lead time. Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic parts. Download Now
Design for Additive Manufacturing (DfAM)
Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a part’s function at the center of their design considerations. Download Now
Taking Control of Engineering Documents
This ebook covers tips for creating and managing workflows, security best practices and protection of intellectual property, Cloud vs. on-premise software solutions, CAD file management, compliance, and more. Download Now

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close