# Propane tank volume

Does anyone know the EXACT cubic capacity of air at ambient atmospheric pressure for a 20# propane tank? That is, a tank that has the valve opened,
then left open until all the contents have gone out, and still has that empty space. I need to figure out the underwater lifting capacity of one of these tanks. And yes, I know I should shut the valve.
Steve
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Since you want the lifting capacity, measure that directly, not round-about with volume, tank weight, & math. Jim was on the right track, if facetiously: water in a trash can & immerse the propane tank. Measure the force required to hold it under. Bathroom scale should be good enough.
KISS!
Bob
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On 28/04/2012 05:18, Steve B wrote:

Once you get your volume, don't forget you'll get a bit more upthrust if it is in seawater.
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Less bouyancy if the tank is made of metal.
On 28/04/2012 05:18, Steve B wrote:

Once you get your volume, don't forget you'll get a bit more upthrust if it is in seawater.
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Stormin Mormon submitted this idea :

Please explain just a little. What has metal got to do with change in bouancy in sea water?

--
John G

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If the tank is made of metal, it will tend to sink. Thus countering some of the air bouyancy.
Stormin Mormon submitted this idea :

Please explain just a little. What has metal got to do with change in bouancy in sea water?
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Steve B wrote:

http://norfolk.craigslist.org/rvs/2984196085.html
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john wrote:

New-Never Used- Propane gas cylinders steel 20 pounds capacity With 10 percent valve for overfill protection, Poly safety plug. Quality construction and a durable polyurethane finish. Specifications: Size 6-1/2 inch x 12-3/8 inch x 18-1/16 inch . LP-Gas capacity (approximate gallons) 5, water capacity 47.7 pounds, tare weight 18.5 pounds, cylinder volume 1,323 cubic inches, collar height 4 inch , footing diameter outside 7-13/16 inch . Manufactured in accordance with DOT-4BA-240.
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47.7 pounds capacity (bouyancy) - 18.5 pounds of steel weight, = 29.2 pounds lift. Of course, there are some other factors, but they are minor.
water capacity 47.7 pounds, tare weight 18.5 pounds,
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Stormin Mormon wrote:

In water the steel weights less. You have to figure the volume of the steel and then add the weight of water for that volume.
John
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wrote in message

Steel's density is 7.85, roughly 8, so the buoyancy is the weight of water the tank can hold minus ~7/8 of the empty weight.
jsw
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That's about what I would have said.
wrote in message

In water the steel weights less. You have to figure the volume of the steel and then add the weight of water for that volume.
John
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