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#19793 - 02/06/14 12:53 PM Re: Brain Games
Midwest Trapper2 Offline
Junior Member

Registered: 03/12/13
Posts: 21
Loc: Indiana
Yes. As a rule, what you have described should happen. I am currently taking a physics class, and from what I've learned, these are the results should receive.

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#19794 - 02/07/14 10:30 AM Re: Brain Games
redsnow Online   content
Moderator

Registered: 06/11/06
Posts: 2050
Loc: WV
Well, I hope all of you guys are still thinking.

Let me ask you this: Just say that I've got my truck sitting on blocks, the truck and all my junk weigh a total of 4,000#, all 4 tires are being changed. One thousand pounds, per corner.

If I pump up my new tires to exactly 60 PSI, with the tires laying on the ground. Now, what will the tire pressure be of each tire, when I add the weight of a 2-ton vehicle?
smile

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#19795 - 02/07/14 03:40 PM Re: Brain Games
FLSH ETR Online   content
Member

Registered: 12/29/04
Posts: 958
Loc: Cudahy, Wisconsin,USA
I was going to 'guess' the answer with my experience with a huge load of firewood that we cut near our deer camp and placed it into my little Dakota truck that I had many years ago. The rear springs went straight, and the tires almost flat. I would guess we still had the same tire pressure, just moved around a little. But I don't believe guessing is the way to answer a challenge. So, I took a hand truck I have, checked the pneumatic tubed tires for pressure, and clamped one tire in a pipe clamp. I cranked it down really good so I had a very flat spot on opposite sides of the tire. Pressure never changed. So your 60#s in each tire will still be 60#s when you apply the weight of the truck on them, only they'll have a flat spot on the bottom, and maybe a little bulging of the sidewalls just above that. smile

Frank. cool
_________________________
"The only constant----is change."

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#19796 - 02/11/14 10:46 AM Re: Brain Games
redsnow Online   content
Moderator

Registered: 06/11/06
Posts: 2050
Loc: WV
I hate to guess at stuff too.

Tell you how this discussion started, a friend was watching me pump up a tire. He said something like this: I never could understand, why, if you inflate a tire to 60 psi, and then add the weight of a vehicle, it doesn't change.

Thanks Frank for your experiment. smile The volume of the tire is the same. It's sealed up, locked inside.

Correct me if I'm wrong! But the air pressure inside of a tire will increase, as the temperature rises.

Just say that the truck does have a HUGE load of firewood, and we're driving down the road 40 miles per hour. The sidewalls of the tires are really flexing, too hot to touch after 3 miles. The tires are getting soft, and the air inside expanding. That's likely to cause a blow-out. Correct?

But let me ask you this: Just say that I have an air tank, exactly 1-cubic foot in size. At sea level, zero pressure inside the tank, it contains exactly 1-cubic foot of air.

Now, just say I'd pump that tank up to 100 psi, how many cubic feet of air would that translate to, at zero pressure?

Or look at a scuba diving tank, exactly 1-cubic foot in size, pumped up to 3,000 psi. How many cubic feet would we have at sea level?

I know that there's a formula, without searching all day, what's the answer? I'm just curious! smile

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#19797 - 02/11/14 12:04 PM Re: Brain Games
FLSH ETR Online   content
Member

Registered: 12/29/04
Posts: 958
Loc: Cudahy, Wisconsin,USA
Air pressure and heat? Years ago on a residential construction site my crew and I were sitting around having a couple of brews. (you can't do that these days) One fella bet that the tires in the sun on his truck had a higher air pressure than those on the shady side. One dude put his digital gauge on all four tires, then the truck was turned around. After a couple more brews we check the tires again. Sure enough, the pressure changed according to the sunlight allocation, with the warmer tires having a higher pressure reading. Certainly not enough of a difference to make driving difficult, but a few pounds none the less.

Not sure about your Q's about cubic ft. I do know that nowhere on earth is there zero pressure. That was a problem with designing the space shuttle. Pneumatic tires to soften the landing could not be installed ready to go because they would blow up in the vacuum of space. Still don't know how they solved that problem, but somehow they got it to work. But you know, unlike water or oil, it's easy to compress air. They sell things called 'air compressors'.(joke here) I drained all of the air out of one of mine and headed to camp. With the thing being in the sun all the way, I was able to release more air when I got to camp. But that's the heat thing again. If the container is constructed properly for the use, any amount of air can be installed. I know they test scuba tanks under water in a swimming pool, in case of failure. Gotta be cool to see one fail!!

Frank.
_________________________
"The only constant----is change."

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#19798 - 02/11/14 12:40 PM Re: Brain Games
redsnow Online   content
Moderator

Registered: 06/11/06
Posts: 2050
Loc: WV
Because PULSAIR uses compressed air or gas to operate, it is helpful to understand how the volume of compressed air is calculated.

A standard cubic foot of air is the amount of air in one cubic foot of space at 70 degrees F and 14.7 PSIA, i.e. standard atmospheric conditions. Since pressure gauges do not register atmospheric pressure, 14.7 PSIA equates to 0 PSIG. Because this is approximately the way air exists in nature, air at atmospheric conditions is also called "free air". Therefore, 1 Standard Cubic Foot of air is the same as I cubic foot of free air.

A tank with a volume of 4 cubic feet holds 4 Standard Cubic Feet of air at atmospheric pressure (0 PSIG). If we inject air into the tank until the internal pressure is 44.1 PSIG, we have 4 cubic feet of air at 44.1 PSIG. How many Standard Cubic Feet of air is this?

Answer: Divide 44.1 by 14.7 = 3. This means that at 44.1 PSIG each cubic foot will contain three atmospheres plus the original 1 atmosphere that existed before pressurizing, or a total of 4 atmospheres. Multiply 4 cubic feet of volume by 4 atmospheres = 16 Standard Cubic Feet of air.

If we inject more air and double the pressure to 88.2 PSIG, the same math tells us we have 28 Standard Cubic Feet of air in the 4 cubic foot tank (88.2/14.7 = 6 atmospheres + 1 atmosphere = 7 atmospheres x 4 cu. ft = 28 SCF).

By using this standard unit of measurement we greatly simplify discussions and calculations of air volumes.

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#19799 - 02/11/14 12:55 PM Re: Brain Games
redsnow Online   content
Moderator

Registered: 06/11/06
Posts: 2050
Loc: WV
Scuba tanks are available in a range of sizes, pressures and material. The most common volumes are 72, 80, 95, 100 and 120 cubic feet, and tanks are made of either aluminum or steel. High-pressure tanks are designed with higher pressure capacities to hold more air per given volume. Steel tanks are neutrally buoyant, unlike aluminum tanks which become more positively buoyant as air is depleted (requiring more weight to maintain depth underwater). Divers use this information as part of dive planning because it affects their weight system, and air consumption determines the length of time underwater.


http://www.ehow.com/how_5700210_determine-volume-scuba-tank.html

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#19800 - 02/11/14 01:04 PM Re: Brain Games
redsnow Online   content
Moderator

Registered: 06/11/06
Posts: 2050
Loc: WV

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