TargetTalk

We (MIT pistol team) have a number of TAU-7 CO2 pistols that we fill from the 150 gram CO2 cylinders. We've been putting the "empty" tanks in the freezer and leaving them there until we are ready to fill them (typically the next day).

This often results in the tanks being over-filled, which we have been told is not a good thing. Putting the tanks in the freezer for a short, measured time as some people have recommended is not practical for us.

What we would like to do is to have a refrigerator (not a freezer) set to the proper temperature for putting a full charge in the cylinder, so that we could put the "empties" in and leave them there indefinitely. What should this temperature be?

About 20 degrees (F) below your fill tank temp.

I find putting the cylinders in the freezer for only five minutes before filling is enough to get a good fill. If you "overfill", just shooting sighters and warmups are enough to "settle" the gun.

Man you guys are from MIT, I'd think the best and brightest minds would figure that out no problem.

On the serious side it depends what the ambient temp is because thats what your big tank will most likely be at the process is driven by differential temps. You want the cylinder chilled so that it fills with liquid CO2, the pressure is regulated in CO2 guns by the fact of the constant pressure of a gas over a liquid. So too cold its all liquid and no gas, too warm all gas no liquid.

If you run into my friend there (goes to MIT) say hi for me his names Beckett, Asian guy from Canada.

We have a fridge/freezer at the range and 10 minutes in the freeze is enough to get an "overfill". We also have a digital kitchen scale to check against the manufacturers recommended fill weight. If you get to much, just push the valve pin for an instant to let out a little bit. Don't freeze your fingers while doing this!

If you leave them in the freeze overnight, you may just take them out a little while before filling.

I guess I'm not smart enough to understand how overfilling the TANK could be a problem.
The pressure in the smaller tank is still dictated by the temperature.
If it safely holds 900psi at 85 degrees or whatever, it shouldn't matter whether the tank is half full or has nearly all liquid, the pressure is the same.

The GUN, on the other hand, may not operate properly if there's too much liquid, so it's easy to see how over filling the GUN might be a problem.

I have an Aeron B-96, using the same what? 150gm cylinder from which I fill the gun. I have left the cylinder in the freezer overnight ( usually put the bulk tank in the sunny window, too). Haven't blown a blowout yet.

Tau 7's, great choice!
Overfilling the Tau's with the bottle is VERY difficult..
I freeze about 10min.
You need sufficient temperature difference for a good fill. Especially with cold winters that might not be too easy.
Buy the way, you can simply blowoff excess CO2 from the cilinder.
You can also keep yr filling procedure you have now, but shorten the filling time.

The fact that the reservoir on these pistols is vertical (in the grip) does indeed make overfilling difficult. The valve will never see liquid unless you shoot it upsidedown.