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Old 01-24-2013, 02:45 AM
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Default What's in that bottle?

Today, I swapped my almost empty Q-sized Argon tank for another. I asked the clerk how many pounds of gas the new tank held, and she replied that she didn't know. She told me nobody had ever asked that question before, and said the tank held 83 cubic feet.

When I got home, I attached the gauge, and turned on the valve. The gauge revealed there was 1,900 psi of gas. The last time I swapped tanks of the same size, the new one had 2,200 psi.

So, I question how tanks that supposedly hold 83 cubic feet can vary in psi. Seems like a rip is being perpetrated. This is not the first time an 83 cubic feet tank has measured at about 1,900 psi.

Am I missing something, other than 300 psi of gas? How does one measure cubic feet of gas in a tank?
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Old 01-24-2013, 03:06 AM
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your psi will depend on the temperature....my guess is they "hotshot" your bottle.
When filling, the bottle will get hot and read a psi telling that it if full...after it cools the psi will drop off.
This happen to me and I had a shit hemorrhage on the guy after i took it home and then drove back...got a free refill out of it.
weigh your next tank before and after fill
http://www.uigi.com/ar_conv.html
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Old 01-24-2013, 07:04 AM
o7oBaseMetal o7oBaseMetal is offline
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I go through alot of argon at work. Tanks usually read between 2300 to 2700. We consider 2500 the "full" psi. We're using bigger tanks though. I have an 80 ft tank at home and that usually reads 2500 when it is full.
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Old 01-24-2013, 12:51 PM
Rob65 Rob65 is offline
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Gadgeteer
I have seen this question asked several times on the web.

In order to give you an accurate answer to what pressure your tank needs to be filled to, to hold 85 cubic feet we need to know the internal volume of the tank. I don’t know about how it works in the USA but in the UK all our tanks have the volume stamped on the top.

If you have 1800psi dividing that by 14.7 equals 122 atmospheres. This means that if you have 85cubic feet of gas at 1800 psi the tank needs to have an internal volume of 0.7 cubic feet.

If the pressure was 2000psi the volume needed would be 0.625 cubic feet.

As Boilerman says temperature also plays a part in all this. When filling air tanks for scuba diving we usually fill them to 230 atmospheres which is about 3400 psi. If you fill the tanks too fast they get ‘very warm to the touch’.

Later when they have cooled the pressure will have dropped by maybe 150psi or more. I don’t know about how welding gas tanks are filled but scuba tanks are often put in a tank of water as they are filled to keep them cool.
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Old 01-24-2013, 02:25 PM
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Quote:
Originally Posted by Rob65 View Post
Gadgeteer
I have seen this question asked several times on the web.

In order to give you an accurate answer to what pressure your tank needs to be filled to, to hold 85 cubic feet we need to know the internal volume of the tank. I don’t know about how it works in the USA but in the UK all our tanks have the volume stamped on the top.

If you have 1800psi dividing that by 14.7 equals 122 atmospheres. This means that if you have 85cubic feet of gas at 1800 psi the tank needs to have an internal volume of 0.7 cubic feet.

If the pressure was 2000psi the volume needed would be 0.625 cubic feet.

As Boilerman says temperature also plays a part in all this. When filling air tanks for scuba diving we usually fill them to 230 atmospheres which is about 3400 psi. If you fill the tanks too fast they get ‘very warm to the touch’.

Later when they have cooled the pressure will have dropped by maybe 150psi or more. I don’t know about how welding gas tanks are filled but scuba tanks are often put in a tank of water as they are filled to keep them cool.
Water helps for ruptures too.
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Old 01-24-2013, 02:54 PM
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Shade Tree Welder Shade Tree Welder is offline
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A tank at 2200 at room temp can drop 200-300 psi when cold like 0F.

PV=nRT

Volume is constant, if temperature drops then pressure drops.

T is in Kelvin.
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Old 01-27-2013, 08:31 PM
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Soapy Soapy is offline
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Quote:
Originally Posted by Shade Tree Welder View Post
A tank at 2200 at room temp can drop 200-300 psi when cold like 0F.

PV=nRT

Volume is constant, if temperature drops then pressure drops.

T is in Kelvin.
Don't know about Argon, but oxygen tanks are filled @70deg f 2200lbs.

From my welding teacher in 1961
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