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Old 25 January 2011, 07:26   #1
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tubes pressure / temp variation

Hi,

I have got a boat that I have been looking after for a customer for a while, as it is stored outside the tubes go soft when cold and firm up in warmer weather. The customer does not really believe/understand the difference the temperature can make to the boat tubes pressure.

Is there a slightly more scientific way for me to explain it to him, i.e 10% pressure loss for every 10 degrees or something similar?

Thanks
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Old 25 January 2011, 07:48   #2
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You could get the dumb cluck to watch this:


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Old 25 January 2011, 08:26   #3
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From memory:

Gay-Lussacs law states P1/T1=P2/T2 but you must bear in mind that the temperatures are Absolute so you can't say a doubling of temperature of say 10 degrees to 20 degrees will double the pressure. There's a little constant of 273 degrees to account for in that as well......

HTH
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Old 25 January 2011, 08:33   #4
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tell him to blow a balloon up. then stick it in the freezer over night and look at it in the morning

Or tell him stand outside for 4 hrs in his underwear and see how small and soft things can get
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Old 25 January 2011, 09:12   #5
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If you want to impress him, hold a PET water bottle mouth down over a steaming kettle for a bit. Replace the cap. Run the bottle under a cold tap. Bottle shrinks dramatically.
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Old 25 January 2011, 09:25   #6
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Cold air is denser than warm air, simples.
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Old 25 January 2011, 09:46   #7
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Lets hope he doesn't decide to take up scuba diving
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Old 25 January 2011, 10:10   #8
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Sell him an automatic compressor and fit him pressure relief valves. The tubes will always be perfect and no need to worry about any of that science stuff.
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Old 25 January 2011, 10:30   #9
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as we live in one atmosphere of air all the time will the tubes have this added to the 2psi we blow them up to, so if this is the case my tubes have 16.7 psi of air in them, or am i torkin bollox
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Old 25 January 2011, 10:36   #10
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Quote:
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as we live in one atmosphere of air all the time will the tubes have this added to the 2psi we blow them up to, so if this is the case my tubes have 16.7 psi of air in them, or am i torkin bollox
The tubes do having 16.7psi in them but a gauge reading gauge pressure will only read 2 psi due to atmospheric pressure.
If you use a gauge that reads absolute pressure then it will read 16.7 psi.
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Old 25 January 2011, 10:41   #11
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Torkin bollix

If you hit a particularly big wave and took off in to outer space then you would have 16psi in them

or am I torkin bollix
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Old 25 January 2011, 10:41   #12
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I think its all down to Boyle's Law, which according to Wikipedia says -

Boyle’s law states that at constant temperature for a fixed mass, the absolute pressure and the volume of a gas are inversely proportional. The law can also be stated in a slightly different manner, that the product of absolute pressure and volume is always constant.

So if you reduce the temperature the volume reduces as well.

We all get floppy tubes in the cold weather!
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Old 25 January 2011, 10:46   #13
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Quote:
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Torkin bollix

If you hit a particularly big wave and took off in to outer space then you would have 16psi in them

or am I torkin bollix
yep you're torkin bollox, the air is colder and not ambient or am i still torkin bollox
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Old 25 January 2011, 10:59   #14
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yep you're torkin bollox, the air is colder and not ambient or am i still torkin bollox
I was thinking along the lines of there's no atmosphere in space so your tube pressure would go up by 1 atmosphere (relative to the atmosphere outside the toob. I might just shut up now before I make a complete fool of myself
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Old 25 January 2011, 11:21   #15
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yep you're torkin bollox, the air is colder and not ambient or am i still torkin bollox
Ambient simply means the surrounding "normal" environment. Ambient on a hot day may be 90 degrees F; on a cold day, 30 degrees F.

Ambient temp in the space example is kind of moot, as there's no gas to measure a temp from. The temps recorded by astronauts are usually read off other surfaces.

jky
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Old 25 January 2011, 11:29   #16
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What about air pressure rather than just temp?

900mb is 13psi

1000mb is 14.5psi

Also bear in mind that the temperature of the air inside the tubes will go up like the seats of a locked car, no air moving in or out to adjust it so pretty warm inside on a sunny day.
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Old 25 January 2011, 11:51   #17
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i think......










we've all got too much time on our hands
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Old 25 January 2011, 12:24   #18
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Quote:
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What about air pressure rather than just temp?

900mb is 13psi

1000mb is 14.5psi

Also bear in mind that the temperature of the air inside the tubes will go up like the seats of a locked car, no air moving in or out to adjust it so pretty warm inside on a sunny day.
Indeed - but also a few drops of water will make a big difference to pressure fluctuations if condensing/evaporating.
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Old 25 January 2011, 12:34   #19
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Indeed - but also a few drops of water will make a big difference to pressure fluctuations if condensing/evaporating.
You should see the effect of a few drops of homebrew on pressure fluctuations!
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Old 25 January 2011, 12:36   #20
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If you can't understand why your tubes go up and down due to a fluctuation in air temp then I suggest you have a look on here: http://www.boatmad.com/forum/
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