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Re: Check valves for CO2

> Date: Tue, 26 Sep 2000 14:11:03 -0500
> From: zxcvbob <bob at area51online_net>
> James Purchase <jpurch at interlog_com> sez:
> > I suppose that they are concerned about water from an aquarium getting
> > sucked backwards and into things like Needle/Regulating Valves and/or
> > Regulators. 
> I don't trust check valves, and I doubt that they are really
> necessary...    
> Check valves are used on welding regulators or torches to prevent having 
> oxygen and fuel gas mix in the regulator or tank, possibly causing an 
> explosion.  Check valves are used in plumbing to keep contaminated
> water out of the fresh water supply lines.  Why do we use them again?

If water gets back to the equipment, water + CO2 = carbonic acid which is mildly 
corrosive.  I think that's the reason El Cheapo check valves melt down when used 
for CO2. 

A check valve might be useful for more than keeping water from siphoning or 
being pushed back by under pressure. I've seen a phenomenom I can only speculate 

We had a Tetra CO2 bell setup some time ago as a trial. Airline ran from the top 
of the bell to a small CO2 tank. I would squirt some CO2 in twice a day to keep 
the bells full. It wasn't very successful.  

However, I did note that when the bells were empty (i.e., all the CO2 diffused 
into the water), the water would slowly move back up the airline toward the CO2 
tank. If I waited long enough, the water would get as far as the tank. There was 
no pressure from the water in the bell - the water had to go up and over the 
tank rim. 

I figure the CO2 in the airline was continuing to diffuse into the water in the 
airline and the water was being pulled back up the line by the relative vacuum 

I tried a check valve to block it and it did, until the guts melted. 

George Booth in Ft. Collins, Colorado (booth at frii_com)