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

Trunnion Ball Valve - Fire Safe Seat Design

Trunnion Ball Valve - Fire Safe Seat Design

Trunnion Ball Valve - Fire Safe Seat Design


Many trunnion ball valve manufacturers show a fire safe graphite seal located in a closed groove on the trunnion seat carrier.
As this is a closed groove, the graphite will have to be split/scarfed in order to fit. Maybe die formed ring or braided packing section.
Does anyone know how this design will seal against pressure if the O-Ring/Lipseal burns out during a fire test?
I'm puzzled as to how the split seal will hold pressure - granted, there is a generous leakage rate during a fire test.

Thanks in advance.

RE: Trunnion Ball Valve - Fire Safe Seat Design

Hello Gray76

Your question started me thinking.

Please take into consideration the difference between a firesafe designed valve and a firesafe tested valve. As you know, a (real) firesafe valve is firesafe only after it has passed a test of going trough a real fire, according to one of the approved firesafe tests regulations.

This twists the question to how the sealing will behave and seal according to the details of the approved leakage test after the fire. There is also the question if all such designs as described will require a split O-ring. Without knowledge details, I wold imagine this problem is technically overcome, one way or another.

RE: Trunnion Ball Valve - Fire Safe Seat Design

Hi Gerhardl,

I was referring specifically to fire tested valves - API 607 etc.
Not sure about split O-Rings, never seen those before on a trunnion seat.
I'm still none the wiser as to how a split graphite seal will hold pressure sufficiently to pass fire test.
I supplose it is possible (on larger valves or thick walled forged valves) that the soft seat seals do not actually burn out within the test period.

RE: Trunnion Ball Valve - Fire Safe Seat Design

When assembled into the valve, the OD of the graphite seal is compressed. When the OD is compressed, the split ends are pushed together and provide a good enough seal to minimize the leak during and after the fire test.

RE: Trunnion Ball Valve - Fire Safe Seat Design

Thanks bcd,

So the amount of compression will be key.
I would also imagine that the seal density and scarf profile will also be critical?

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


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