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Old 12/02/10, 04:58 PM
Calfkeeper's Avatar
Chief Bottle Washer
Join Date: Feb 2006
Location: Missouri
Posts: 548
"How much does a gallon of air weigh?"

This question was seriously posed to my husband's friend, "Tom." Seems this guy had a little dump bed trailer and had rigged two air tanks on it, one on each side (or end, I am not sure how it worked). He was going to fill one tank at the front with air at the beginning of the trip. Then change the air to the other tank in back to help dump the load.

Seriously. He was serious.

Tom said that when the guy asked him that he, Tom, just stood there and looked at him; did not know what to say.

After my husband and Tom had yukked themselves silly over it, I noted; "Well, obviously the guy was looking at the gauge, which probably said something like 100 POUNDS or such, and took it literally."

Yes, the guy in question is from the city. But still.

We got a kick out of it.
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Old 12/02/10, 05:18 PM
Join Date: Nov 2004
Location: SW Ohio
Posts: 188
Hmmm, I have an air compressor, and now you've got me wanting to weigh it before and after I fill it!

It's just a little portable one, but it must weigh more when it's full of compressed air. I can't imagine it would be much different though.

Perhaps I will haul my bathroom scale out to the yard and conduct a small experiment. I will report back if I do!
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Old 12/02/10, 05:23 PM
po boy's Avatar
Saltine American
Join Date: Jul 2010
Location: Watertown, Tn.
Posts: 3,249
robin, I hereby grant you that assignment. Please report your findings within 24 hours.
I can't wait!
Mortgage Underwriters
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Old 12/02/10, 05:27 PM
In Remembrance
Join Date: Jun 2002
Location: South Central Kansas
Posts: 11,076
Here is another one for you to ponder, how much does a soul weigh, as determined by weight of a body on scales before and immediately after death?

I'm sure the scientists that performed that weighing task are still scratching their heads as the body weight DID change when the person died.
My family---bEI
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Old 12/02/10, 05:35 PM
Join Date: Jan 2004
Location: MN
Posts: 8,101
Thanks for the chuckle.

Quick answer: He can make a 10 lb change.

For an answer, one would have to know how much the air is compressed as well as it's temperature, which make a big difference. Air at sea level weighs a tad more than air in Denver, with the altitude. But, the air floating around us in general weights .08 lbs per cubic foot:

1 cubic foot of air at standard temperature and pressure assuming average composition weighs approximately 0.0807 lbs.

For compressed air at what is normal homeowner pressures & temperatures, he could get it up to about one lb per cubic foot.

So, if his tank is an 80 gallon on each end which is about 10 cubic feet, he could affect the dumping effect by about 10 pounds.

Sorry if I'm turning this techincal but looks like you got people interested in the numbers, so.... I loved the belly laugh, thanks.

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Old 12/02/10, 05:42 PM
lisa's garden's Avatar  
Join Date: Apr 2010
Posts: 736
Depends on what planet you are on

It would weigh a lot more on Jupiter, for instance :baby04:
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Old 12/02/10, 07:57 PM
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Join Date: Feb 2007
Location: Ohio
Posts: 4,056
One square inch of the "air column" at sea level weighs 14.2 lbs.
"Those who hammer their guns into plows will plow the fields of those who don't."-Thomas Jefferson
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Old 12/02/10, 08:25 PM
Join Date: Dec 2008
Location: ne colorado
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goes along with, what weighs more, a pound of feathers or a pound of gold.
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Old 12/02/10, 08:34 PM
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Posts: 686
a pound of feathers weighs more.
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Old 12/02/10, 08:43 PM
Join Date: Dec 2007
Location: East TN
Posts: 236
I had an employee filling up a small air tank one time and was picking it up to see if the weight had changed. We all got a big chuckle out of that.
A man can never have too much red wine, too many books, or too much ammunition. Rudyard Kipling
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Old 12/02/10, 09:52 PM
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Join Date: Nov 2005
Location: Ocklawaha, Florida
Posts: 390
This reminds me of my cousin (he died years ago) Anyway he was working for me as a plumbers helper many years ago. We tested some pipes with air pressure if water was hard to come by at the location. We was at a gas station filling up a large air tank one time and had 120 lbs of air in the tank. The tank was heavy anyway and he asked how in the world are we going to get this to where we need it ? I asked him what he was talking about ? he said it is all I can do to carry that tank empty and you just put a 120 lbs into it no way the 2 of us can carry it now.
It took me a few min to be able to explain it to him as I could not even talk for a few min.
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Old 12/02/10, 10:16 PM
Rat Racer
Join Date: Sep 2010
Location: New Hampshire
Posts: 680
Well, he said it was 120 pounds per square inch. I don't know how many square inches the tank is, but I know I'm not even going to try to lift it!
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Old 12/03/10, 03:50 AM
Join Date: May 2002
Posts: 7,154
If his back tank isn't full of air all the time, what is in it??
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Old 12/03/10, 06:19 AM
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Location: North Alabama
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When we were developing some hardware where I worked our mechanical engineer had to take the weight of the liquified gases and containers in the part of the assembly our hardware was located into consideration when buying off on our electrical design and when I said at least the air weighed less than our hardware he told me that our circuitry had to weigh less than 3 pounds because the liquid oxygen in the tank located within the allotted weight area was about nine and a half pounds per gallon volume and the weight of the tank combined with the O2 volume forced us to keep our design under 3 pounds to remain within the flight specs.

He further demonstrated the weight of air at different mass compressions by picking up two disposable compressed air duster cans and showed the difference in weight of a full and empty can.

Not only was I reintroduced to the maximum weight of stored O2 that day, I also learned that engineers were often born without the gene that provides humor. Of course he was right and reminded me of one of those many factoids from my intro physics class that I knew I would never face again after passing the test
"I didn't have time to slay the dragon. It's on my To Do list!"
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Old 12/03/10, 06:56 AM
Join Date: Dec 2003
Posts: 3,693
Well, the air does have weight, and if the tanks were large enough, it could be a significant amount of weight.

However, this is not an issue in this case. The 100 lbs on the gauge was lbs/square inch, a pressure reading.

Very generically and with a total lack of calibration, my little ~5 gallon portable pressure can changes weight by about 3-5 lbs I'd say, when going from empty to fully charged at 100 psi.
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Old 12/03/10, 09:35 AM
Join Date: Nov 2008
Posts: 5,859
I was going down the road behind a pickup with a cap on the back. Suddenly the pickup stopped in front of me, the driver got out and pounded on the side of the cap with his hand. He got back in the pickup and drove on.
A few miles later, he stopped again, and proceeded to pound on the side of the cap again. I yelled at him, "What in the world are you doing, stopping and pounding on your truck like that?' He yelled back, "Ive got a ton of canaries in here! Since this is a half-ton pickup, I've got to keep half of them in the air at all times!"

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Old 12/03/10, 11:17 AM
Join Date: Mar 2006
Location: Michigan's Thumb
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Originally Posted by lisa's garden View Post
Depends on what planet you are on

It would weigh a lot more on Jupiter, for instance :baby04:
That makes "compressed air" take on a whole new meaning.
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Old 12/03/10, 11:41 AM
Join Date: Aug 2010
Posts: 117
Originally Posted by rancher1913 View Post
goes along with, what weighs more, a pound of feathers or a pound of gold.
A pound of feathers weighs more than a pound of gold.

Precious metals such as gold are measured in troy weight. A troy pound is 12 troy ounces, and each troy ounce is 480 grains, making a total of 5760 grains to the pound of gold.

Most materials use pounds and ounces from the avoirdupois system, and such a standard pound is made up of 16 ounces, where each ounce is 437.5 grains, making a total of 7000 grains to the pound of feathers.

All this means that a "pound" of feathers (or bricks, or lead) is heavier than a "pound" of gold.
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Old 12/03/10, 01:05 PM
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Join Date: Jan 2008
Location: Florida and South Carolina
Posts: 2,193
An aluminum scuba tank holds 80 cubic feet of air when compressed to 3000 psi. The difference in weight is about 6 lbs, which jives closely with what rambler listed as the weight per cubic foot.
"What one generation tolerates, the next generation embraces." -John Wesley
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Old 12/03/10, 03:24 PM
sammyd's Avatar  
Join Date: Mar 2007
Location: Central WI
Posts: 5,760
unless he has an air compressor just cross connecting the two tanks will only balance out the air thus having no positive effect on the dumping process at all.
Deja Moo; The feeling I've heard this bull before.
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