Is it safe to assume that a 5 # co2 tank should weigh 5# more when full than empty?
Every time I have gotten mine filled it is less than 3 #s. Today I had it filled and it weighs 1# 14.4 oz more than when it was empty.
I questioned the guy before and he gave me some BS about it may heat up and expand so they can’t fill them to 5#s.
I fill my 10# tank up at a local fire supression place and they weigh the empty bottle and add 10 pounds. I’ve watched them do it. It may be a little less than 10 but it’s in the ballpark.
While the gas is cold, I doubt you’re loosing 4 pounds.
A 5lb tank should hold 5lbs of CO2. The gas is under enough pressure to become a liquid. I don’t want to be harsh but he either doesn’t know what he is talking about or is intentionally lying to pad his profits. Hopefully you can find a different supplier. I use a fire equipment company for my refills. Look for “carbonic” suppliers in you area.
Paul
Its like Blue Rhino only putting 15# in a 20# propane tank “for safety”. When my local guy fills my propane tank, its 20# heavier.
Sounds to me like you need to find another place to get your tank filled. I just swap my 5# tank out at Airgas, but I have them refill the 15# tank.
+1. That’s why the call it a 5# tank 
Check if you have SimplexGrinnell in your neck of the woods. They fill my tanks here in Vegas. Airgas is another place.
Temperature change isn’t going to affect weight/mass.
Thanks for all the input. It is exactly what I assumed. I questioned the guy this morning. he had all kinds of excuses. I have found a new supplier. He’s a little further away, but for a full tank it’s worth it.
Thanks again,
dwhite55
Well, sure, maybe for non-relativistic physics …
By the way, do places that fill CO2 bottles generally also deal with propane? Most of the places I see for propane (gas stations, big box stores, grocery stores) all have the Blue Rhino setup and I’d like to see what other options I have.
It would affect pressure which is the real concern with a tank. But still, 2lbs in a 5lb tank would be 60% headspace - overkill. I would think a 5lb tank is certified to hold 5lbs of CO2 and still have space for expansion, but I don’t know the specifics of tank certification.
A compressed gas supply company might do both, but otherwise its probably one or the other. Look for places that sell propane for heating, they usually fill BBQ tanks too.
Of course, if the tank isn’t completely empty when you bring it in, that may be a different story.
I don’t think there are requirements that say a business can’t do both but here in Des Moines they seem to devide alone fuel and non-fuel lines. I can find dive shops that fill CO2 and oxygen, carbonic suppliers that just fill CO2, fuel companies for just LP but I haven’t found anyone who does all 3. At a retail level at least.
Paul
You should call the dept of weights and measures in your state, they calibrate and monitor for accuracy on all devices. Maybe the state official can set him straight.
OR just pay him by the pound like my propane guy, and not per tank.
My local brew store sets the CO2 tank on a scale, zeros the scale, then fills the tank to 5 lbs. (and only charges $10)
Sounds to me like he doesn’t know how to fill a tank. My local fire guy fills mine and I think he probably wastes as much as he puts in because he says the tank has to be cold in order to fill properly so he fills (puts gas ins) and purges my tank 3 or 4 times until it’s frosty and then fills it. I think if you just hook up a warm tank you can’t get 5 lbs in due to the expansion or something.
Either way you’re getting ripped off.
We fill propane tanks by weight. I don’t know if it’s the same, but if the tank was improperly purged (there’s air in there) that will throw off the weight, and limit the amount of propane that will fit in the tank. If it’s really hot outside (100*F+), it’s hard to fill a propane tank 100% full. It makes total sense that your CO2 tank won’t hold 5lbs if it’s hot. Unless they cycle CO2 to cool it off like gmac described, it just won’t all fit in there.
Good idea. They may regulate it and they surely can tell you what an acceptable fill level is for your tank.
Someone called weights and measures on us once, because of this problem with a short fill. They came out, tested our scale, said it was fine, and left. They come out every year to test our equipment anyway (scale and the flow meter for RVs). It’s not likely that the scale is the problem, or that you’ll do anything but waste a bureaucrat’s time.
I’d call the BBB if you think you’re getting ripped off.
(We only charge by the pound, BTW, so we only charged him for the short-fill amount, but he was still pissed).
In Delaware they do far more than scales. They’ll test almost anything in a pre-measured package to make sure it contains what the measurement says.
But it might be easier to get the tank filled at a place you KNOW won’t rip you off (like a pressurized gas distributor that deals with lots of commercial customers. Weight it after filling and then you know what the other guy should be filling to. If they short, tell them and go elsewhere.
If CO2 is anything like propane, this is true. Our equipment has a pressure safety mechanism. Hot gases expand. If the tank is hot, the propane will expand, tripping the pressure mechanism on the filling device before the desired weight of gas is in the tank. At that point, the machine can’t put any more propane in the tank.