Plug - Ball Valve Venting in Fire-Safe applications 1

[Allent2002]

I have done an exhaustive seach on the site for recommendations for Venting of Ball or Plug Valves where FireSafe Applicatons are needed. Can anyone offer some insight or recommendations? Generally (as I understand) it is an industry standard to have a vent on the side and valve installed where (when turned) has the vent facing upstream. There is also a manufacture that Vents to the bottom. Does an industry standard exist - or is this end user preference??
Thanks in advance for your replies.

 

[bcd]

No, there is not an industry standard for venting the cavity between the seats. It is up to each manufacturer to establish a method to prevent excessive pressure increase within this cavity. All that is required is that the valve pass the fire test.

ASME B16.34, paragraph 2.3.3 says it is the end users responsibility to know when fluid expansion will be a problem on double-seated valves and to ask for a method for reliving this pressure. So end-users can have in their valve specifications a description on the specific way the pressure is to be relieved. I.e., a small hole through the side of the ball, a vent line from the bottom of the cavity to the upstream side, self-reliving seats, etc.

 

[breaker34]

@bcd...I was thinkng of this question just recently myself. My question is, there isn't a regulation temperature point at which a self relieving or by pass system be used to vent the ball caivity? I imagine this could be differnet based upon the media like you mentioned. Some expansion temperatures could be much lower or higher for different processes.

 

[bcd]

Hello,

No, there is no standard temperature because there is a wide variety of non-metallic sealing materials used in these valves which results in a wide variety of temperature ratings.

There are a few standards that limit the maximum body cavity pressure at 1.33 times the rated pressure. The seats, relief valve, or however the cavity pressure is relieved shall not allow the pressure to exceed 1.33 times rated pressure. The basis of 1.33 is that it is less than the 1.5 shell test pressure the valve was subjected to, so it is a safe limit. Problem is that this 1.33 limit does not work for small valves using self-relieving seats, where it is common to use the same seat in Class 150, 300, 600 and 800 rated valves. To comply, the manufacturer must put a hole thorugh the side of the ball which now makes the valve only one way tight.

 

[Allent2002]

THat is what I had learned - Thanks for your input !