# What psi should read on a 10lb co2 tank



## jstehman (Dec 13, 2010)

If I remember right, at 70 degrees your high pressure should read 800-850psi. The pressure will rise as the temp increases.. just can't find the chart right now.


----------



## PlantedRich (Jul 21, 2010)

Interesting question and I feel it is somewhat related to temperature. But then I was talking to the friendly gas refill guy and got some thoughts on how they feel about gauges. They look at gauges as helpful but not really that accurate as there are so many things that effect the reading. Temperature, age of the gauge, how much gunk and corrosion have built up around the gauge are some he mentioned. 
Bottom line was that they go by weight. He showed me the T.W. (tare weight) on my tank and told me to weight it if I wanted to get a true reading of how much liquid I had. 
I have an electronic scale and the first weight I got was tare plus 10.2 lb. Next three tries on weight got me 10 lbs even. 
I'm considering whether it is worthwhile to put a scale under the tank and leave it as it would be a far better indicator of what I had left.


----------



## ryu1 (Aug 26, 2011)

It was quite cold this morning, so it might have an effect on it. Hey, I paid the same amount and get maybe 20% less gas, thats not right. Maybe I am wrong, I will check my gauge at home after work, I would think the pressure should stabilize after 10hrs in room temp.


----------



## Bettatail (Feb 12, 2009)

dig hoppy's thread, he has a chart about the temperature and the pressure.

weight the co2 tank is the sure fire way to know how much co2 inside.
sometimes, the HP gauge is not accurate, it is about 3-5% error for most of the gauges even they are brand new, that is about 25-40 psi off.
And if you have a bad habit turning the co2 tank on fast, the pressure shock will damage the elastic coil in the gauge, more error on the gauge.


----------



## Darkblade48 (Jan 4, 2008)

Found this neat little graph:

http://www.plantedtank.net/forums/showthread.php?t=178437#10


----------



## ReluctantHippy (Jun 23, 2011)

CO2 tank pressure, as long as there is still liquid CO2 in the tank, only varies based on temp, not how full your tank is. A half filled tank and a full tank will read the same pressure at the same temperature. To figure out how much CO2 your tank has you need to weigh it.

Great resource here that breaks it all down - http://www.reefscapes.net/articles/breefcase/co2_tanks.html


----------



## PlantedRich (Jul 21, 2010)

ryu1 said:


> It was quite cold this morning, so it might have an effect on it. Hey, I paid the same amount and get maybe 20% less gas, thats not right. Maybe I am wrong, I will check my gauge at home after work, I would think the pressure should stabilize after 10hrs in room temp.


Is the pressue reading the only thing that makes you feel shorted? I would ignore that. Is this a tank which was exchanged or did you have your tank filled? 
My reason for asking is that I have thought about how to tell if I'm shorted and came to a big thought. 
I get my refills by exchanging tanks at a welding supply where they have like 40-50 tanks lined up full and ready to go. I pay $11 plus tax for ten pounds so it runs about a buck a pound. This is something they do in mass quanity for lots of different customers. Most customers are repeat as the tanks are marked for this dealer. 
For them to short me even as much as a pound of gas, they would be risking offending some of the big customers as they never know which tank will go where. With that in mind and seeing their "profit" from cheating me would be all of a buck, I feel pretty sure they don't bother. 
How many customers would they have to cheat to make it worthwhile to lose a few customers along the way?

I think I can trust the gas place much better than my bank!


----------



## ryu1 (Aug 26, 2011)

I went home and check the gauge, same reading no changes. I usaually turn on co2 slowly, so i dont think the gauge is damaged. Anyway, i will see what i get in the next few months when i do another swap. Thanks all for all the input and links.


----------



## oldpunk78 (Nov 1, 2008)

Slightly off subject but maybe this will help with worries about over filled cylinders. The last time I went to get my tanks filled at the local fire protection company, the guy mistook my #2.5 tank for #5. He came out saying that he couldn't quite get it all the way filled. Only 4lbs... 

I go: that's only a 2 1/2lb tank. He goes: oh... Goes back and dumps it, comes back out, says this ones on him and sends me on my way. It's currently at about 1500 psi. My relief valve is a high one for some reason, , 2300psi. Most are hydro'd to 2000psi. A 100psi here and there isn't a big difference. Especially if you've got cheap gauges that are probably off a little anyway.


----------



## ryu1 (Aug 26, 2011)

Regulator is from gla, is that a cheap gauge? lol


----------



## HD Blazingwolf (May 12, 2011)

Well, a 1 lb and a 20 lb tank will have the same pressure at the same temperature as long as they both have liquid co2 in them.
so if its full by weight then the PSI does not matter

EDIT: every tank should have a Tare weight, and a full weight stamped into it. go by that measure


----------



## PlantedRich (Jul 21, 2010)

WOW! That really makes me happy to not try any of the hobby type places for refills. If a guy doesn't know a 21/2 from a 5, he may be missing quite a lot of the important stuff. Like how to avoid blowing things up!


----------



## oldpunk78 (Nov 1, 2008)

^ the normal service tech left early that day. The guy who did it was an older gentleman who doesn't fill stuff on a regular basis. The normal guy is very knolagable and always does it by the book. First thing he normally does is inspect the labeling and last hydro date.


----------



## tetra73 (Aug 2, 2011)

700 at room temp. 800 is possibility the tank has been slightly overfilled. No big deal.


----------

