Valve for CO2

> From: nguyenh at nosc_mil (Hoa G. Nguyen)
> Where can I find a good back-flow-preventing valve for CO2 that won't
> dissolve in the carbonic acid?  And how much did you pay for it?

We use Dupla "Bubble Counters" on our tanks.  Besides acting as a
bubble counter (an easy DIY project), they include a check valve. 
Pet Warehouse had them for around $35 the last time we bought one. 

George in Colorado with a "9" (5 degrees and 4" of snow).