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Old 18 July 2005, 20:47   #1
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Boyle's Law

Any mathematicians out there ,as I am Math challenged
I am taking my rib trout fishing for its vacation in fresh water this week
Going up to the Laguna Mountains at an altitude of over 6,000 ft.

Was thinking for a laugh what size my 50cm tubes would be (If they could stretch and remain at the same pressure ) .

Luckily I have pressure relief valves fitted ,but learned from experience after taking my SIB up there several years ago.The thing was taught enough to pop ,even after 2 pressure relief stops!
Even more fun on the way back when the tubes were normal at altitude and then turned into a "floppy pile of hypalon" back at sea level and almost flew off the trailer.
Trying to get an idea of the differance , so I can let out (say half ) the air at sea level and maybe will be just right when we get there.
Taking orders for trout now
cheers Dal
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Old 19 July 2005, 01:29   #2
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Thanks to a Fish Farm supply company..

A one cubic foot balloon at sea level will expand to about 1.2 cubic feet at 5,000 feet (1,500 meters) altitude.

Link.

Also from a Saab site..

Tyre pressure will increase with altitude. The 30 lbs. of "dense air" you put in your cars' tires at sea level will now represent 40lbs. at Keystone. (Approx 12,000ft above sea level.)

Link.

The second link has some interesting comments about using a two stroke at altitude..
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Old 19 July 2005, 02:04   #3
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Wow,only 1.2 !!! Was somehow expecting a lot more than that.
cheers Dal
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Old 19 July 2005, 03:10   #4
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boyles law

do you want boyles law or the ideal gas law a combination of boyles and charles law, ?? ;boyles law ;vol1 x press1= vol2 x press2 ;charles law vol1 divide xtemp1 =vol2 divide x temp2 ;ideal gas law press1 x vol1 divide x temp1 = press2 x vol2 divide x temp2 .this is worked out using absolute temp i think . i hope this is correct as it is 30yrs since i took my phsics a level !!!
PS dont ask me to do the calculations
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Old 19 July 2005, 09:23   #5
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Yep I concur with Paul. If I remember correctly it is P=VT. Where P is pressure in Pascals (or something like that), V is volume in litres and T is temperatur in Kelvin. It probably doesn't matter what units you use so long as you're consistent.

However, and there is a big BUT here..... it must also depend on any flexibility in the Hypalon as it may expand slightly or stretch at different pressures. For a rigid container, the only change in internal pressure would be if the temperature changes. In the case of your tubes, perhaps the pressure release valves would let more air out than you realised at altitude as the external pressure would be lower therfore affecting the release valves.

I don't know really..... and the above probably contradicts itself somewhat too. I used to be quite good at physics but you wouldn't know it now!

Keith
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