CO2 End of Tank Dump (quoted info)

125gJoe

125gJoe

2009 VMAX
Jul 6, 2002
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I found this from a past discussion in -fishgeeks (dot) com-, and thought it would be informative and interesting about CO2 Dumps..

>>Let's address end of tank dump.

In a CO2 tank you have liquid and vapor. The vapor is what we inject into our tanks. As the vapor is used, pressure in the tank is reduced, the liquid boils off and turns to vapor increasing pressure again. This all happens at a steady rate, so you don't see the fluctuation on a guage. When you reach the end of the liquid your tank pressure will start to drop as the last of the vapor is used. This is where some regulators will have a problem holding pressure and "dump"

Some claim a needle valve will help with this, I don't believe this is the case. If you have a needle valve set, and all of a sudden the pressure going to it increases, so will the amount of CO2 going through it.

So lets take one step back to the regulator. Most of the dual guage (and even some of the single guage) "beer tap" regulators will have an output pressure adjustment. What matters is the "drift" and working output pressure of the regulator. Drift is the varience of output pressure from full tank to empty tank. Lets say your "beer tap" regulator has a drift of 2psi. You set your output pressure at 5psi. At "end of tank" your psi could jump to 7 due to "drift" That is a 40% increase. Can your levels handle a 40% increase? Now lets say you set your output pressure at 20 psi. At end of tank your PSI could jump to 22. A 10% increase. Much better.

I have no hard data on aquarium specific CO2 regulators, but I would bet they are designed with minimal drift. You can find "beer tap" regulators that do the same.

I have used ones with minimal drift for quite some time. I have run CO2 tanks bone dry. My pressure change very little. I have never lost a fish to this, and I run my CO2 levels at the high end of "acceptable". For those that know, yes I do run controllers on some tanks, but I am not speaking of these tanks in this instance.

I am not bashing aquarium specific regulators, I do believe they work. I also believe that if you do your homework you can get a very good, non aquarium specific one that is comparable, cheaper.

Of course all this can be avoided if you watch the tank pressure and refill/replace when you see it drop. <<

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Boos - read the links on Bob Alston's post. They will explain the end of tank dump.
Basically, if you re-fill when your gage gets to 600lbs you will avoid the dump and there's not much CO2 left in the tank at that point anyway.
Len
 
What is the 'normal' reading at full?

I thought mine was slightly about 600lbs. (full), so I'm unsure of when it's getting real close to re-fill time..:confused:
 
yes, 850 psi for the tank. Just be glad you aren't the regulator huh?

I have a dirt cheap beer tap regulator, about 20 years old, and it has tons of drift. I compensate with a $50 needle valve with a silicone bladder in front of it. The bladder is a baloon inside a tube. Under the normal 5psi from the regulator to the needle valve it is about 1/2" round, but during a dump it will swell to 1" or 1.5" so I know to get my tank switched soon. The pressure on the needle valve is never so high that it increases my bubble count though....
 
Originally posted by cpr4cpu
.. .... with a silicone bladder in front of it. The bladder is a balloon inside a tube.....
Click to expand...
I'm trying to picture this 'silicone bladder' and get seem to understand what/how it works. How is it installed...?

Any pics of this?
 
it looks like a tube, about 4 inches in diameter, and rounded at the ends. It reminds me of the packaged meats, like hamburger, that come in the rolls. (or a tft membrane for RO system users).

Inside the tube is a membrane like that found in an RO holding tank (pressurized). It looks like the same stuff that bicyle inner-tubes are made from, but much more pliable. The inside of the tube (outside the bladder) is negatively pressurized (air vacuumed out) and sealed. As air enters the bladder, it expands with almost no force, and the needle valve on the exit end is not "forced" since excess pressure on the inlet side expands the bladder. I assume that once the bladder is maxed out it will increase the pressure on the needle valve, but never managed to get there with only 2-3 psi on the regulator.

It is really a shock absorber for the needle valve so the presure increase during the dump will not force pressure on the needle valve.

I have seen these things sold as sealed pressure relief chambers, but it has been years. Originally I think I saw the devices for scuba diving tanks, except filled with water instead of a negative pressure.
 
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