Best valve type for dense phase CO2 service

[MichelleB]

I am trying to determine the best valve type (ball vs gate) for dense phase CO2 service - both for mainline and for smaller takeoff valves. Is one more suitable than the other in this type of service? Additionally, do you have any experience using plug valves as sacrificial valves when depressurizing or repressurizing segments of pipeline?

 

[zdas04]

I prefer ball valves, BUT you have to be really careful to make sure the manufacturer knows you are using them in CO2 service. Several of the common o-ring materials used in ball valves will absorb CO2 and shred the first time the line is depressurized. All of the ball valve manufactures I've worked with are very aware of this and have materials that are not prone to absorbing CO2. An off-the-shelf ball valve is a disaster.

I don't know what you mean by a "sacrificial valve".

David

 

[MichelleB]

The sacrificial valve is a bypass meant to take the bulk of the pressure differential to protect the mainline valve when refilling an isolated segment of line.

 

[iainuts]

I'm not familiar with your application but thought it prudent to mention that, when CO2 is transferred as a refrigerated liquid, ball valves must be self relieving (ex: drilled ball) to prevent excess pressure internal to the ball. If you trap liquid CO2 inside the ball and allow it to warm up, the pressure inside will be sufficient to blow the valve apart. The same holds true for any sections of pipe between valves, a relief valve must be installed and sized to handle the worst case heat flux.

If your system is strictly ambient temperature, this shouldn't be an issue.

 

[thost]

I think a good valve selection for this service is:Trunnion mounted ball valve with metal seats, PTFE-based seals and self relieving seat design.