What does trunnion mean? 1

[dkf]

I have in hands a local valve mfg catalog that claims " full trunnion ball valve", from the valve assy' drawing you cannot say it can be repaired in line. Valve is built according API 6D, 12" to be used in clear petroleum products pipeline.
TIA
dkf

 

[cranekiran]

Well!
I got this info. for you from a site,Hope it Helps.

Trunnion Design is simply the use of upper and lower supports to retain the ball under pressure. Named for the "trunnion" historically used to support a cannon, a ball valve trunnion essentially doubles the safety and usability of a ball valve.
Another important benefit of the trunnion design is that it allows the Ball Valve to act as a true union: The downstream piping can be disconnected under full upstream pressure (user is responsible to ensure that downstream piping is drained of liquid and that valve is indeed closed and secured to upstream piping).
The trunnion on a two-way ball valve supports the ball in much the same way as the stem does at the top. The trunnion on a three-way ball valve is a much different design, being more like a supporting ring, but provides the exact same function and inherent stability.

For more details you can go to:-

http://www.plastomatic.com/trunnion.html

 

[joeswoes]

Be aware of the downside to trunnion designs so you can make an informed decision. On the plus side, trunnion mounted balls have more assembled pre-load between the ball and seats, thus better low pressure sealing capabilities than floating ball designs. However, because of this, there is usually much higher turning torques and, because it does not float into the downstream seat, line pressure can not assist sealing.

 

[hammerr]

Most trunnion ball valve designs have pressure energized upstream seals.
For a floating ball type valve, the ball is pushed downstream with increasing pressure differential. For an upstream sealing trunnion valve, pressure differential pushes the upstream seat into the ball. Both designs have advantages but I think the biggest difference in function between the two: Floating ball valves are inexpensive and work very well up to about 6 inch size and 300# class. Beyond that, the seat design is compromised to carry the load from the ball. Trunnion ball valves are better suited for larger sizes and higher pressures because the seat surface area exposed to the line pressure drop (amount of pressure assist) can be designed to whatever you want. There isn't much you can do with the ball geometry to tailor the load from pressure drop. And of course as the valve gets bigger, a floating ball gets pretty heavy for the seats to support.