Thread: Ball check valve or gas bubbler

Hello,

I'm trying to figure out what kind of check valve best to use in my system: the system is typically under positive/ambient pressure of inert gas (nitrogen), and the main issue is to prevent contamination by backward diffusion against the gas flow by outside air, specifically oxygen. I know that check valves can prevent or limit backflow when the system is under negative pressure, but what is the best way to prevent backward diffusion against the flow of inert gas going out the system?

Schlenk lines are typically equipped with bubblers rather than check valves, in my knowledge, which leads me to believe that oil is effective in keeping oxygen from diffusing back against the flow. Bubblers are, however, less maintenance-free, and there exists a danger of accidentally drawing oil into the system, which would not be easy to clean up.

I assume ball check valves are also somewhat effective in preventing backward diffusion, since the smaller opening for the gas created by the presence of the ball should increase the pressure at the opening and probably limit the number of particles that could diffuse back. However, do they do as good a job as a bubbler? If not, do they do much worse a job?

I also know that ruby ball/sapphire seat check valves, or even double-ball check valves, are usually deemed superior to metal ball check valves as they are somewhat more durable and more resistant to corrosion. However, I mostly read about those being used in applications such as HPLC or medical, and it seems that their resistance to chemicals is their biggest selling point. Does anyone happen to know if they form a better seal/are significantly more durable than their metal counterparts? Because what reaches the check valve is mostly inert gas, there would be little point in buying a more expensive ruby valve just for the sake of chemical resistance. Higher seal quality or longer lifetime is a different story.

Thank you for reading,
anvoice

l think a bubbler is ok,a properly designed one will not suck back oil and you can put an O2 scrubber column between the bubbler and your system for added insurance.