Hi, just wondering if there are any maths whizz who can help calculate the cubic volume of air required to inflate a tire tube, relative to pressure inside the tube.
The link below should go to a photo of the inflated tube. The tube will be enclosed in a cover that ensure it retains the shape it is pictured at, i.e it is not in open air so it is not going to just keep increasing in size as it inflates.
My reason for asking is I'm trying to work out what 3,000 PSI of bottled air (regulated to 10PSI) is required to inflate, then deflate then inflate the tube 50 times in the field. Cheers
medcare,
May 6, 3:24pm
The 150mm figure is the width of the tube and the 300mm figure is the inflated height of the tube.
farwest,
May 6, 3:29pm
Treat it as though it was straight edged - then diameter of tube X pi X thickness, less diameter of hole X pi X thickness.
farwest,
May 6, 3:31pm
So - (0.5x3.142x.3) - (.2x3.142x.3) approximate volume in cubic metres.
morrisjvan,
May 6, 3:31pm
fill it up with water, measuring the amount you use.
richardmayes,
May 6, 3:39pm
(Treadwidth x sideWallHeight) x (wheelDiameter+ sidewallheight) x pi
Take care not to use inches (wheel diameter) and millimetres (tread width) interchangeably!
tony9,
May 6, 3:44pm
If it was inflated to 15psi it would take double the enclosed volume of air. So 10 psi should be 1.66 times enclosed volume.
tony9,
May 6, 3:46pm
And google "volume of a torus calculator"
medcare,
May 6, 3:51pm
Thanks Tony, 20 years ago I could have worked this out. but not now, as they say use it, or lose it.:-)
What makes it tricky (for me) is the tube height is twice the tube radius, and the 10PSI pressure exponent thingy REALLY messes with my head.
So I appreciate any actual figure volumetric answer that can be supplied.
medcare,
May 6, 3:53pm
The end result I'm looking for is what sized (cubic capacity) dive air bottle, at 3,000PSI do I need to carry to manually inflate and deflate a tube of this size to 10PSI 50 times in the field. Cheers
dublo,
May 6, 3:58pm
This all sounds very interesting, I wonder why he is planning to inflate a tube 50 times? Sorry I can't help with the maths - just too much for me to work out in my head!
chas10,
May 6, 3:58pm
About 40 years since I was at school but I will take a stab at it. I work out the volume of the tube to be approx 77 litres, ie area of the elliptical cross section times the median diameter. To increase the pressure from atmospheric to 10 psi would take approx 45 litres of air. This is assuming no change in temp. Assuming the tube is deflated but retains its shape then to do this 50 times would take 2250 litres of air. If its totally deflated then of course that would need another 50 X 77 litres of air. 2250 litres of air at 10psi would occupy 18 litres at 3000psi so I would say an 18 to 20 litre bottle would be ballpark but I stand to be corrected.
My question is what is it it for?
medcare,
May 6, 4:10pm
Quote ". If its totally deflated then of course that would need another 50 X 77 litres of air. . "
Yes when the tube is flat, it is flat, fully deflated, squashed flat as, with probably no air in it.
When I have the answer I can kinda tell you what it is for (and no, it is not for taking a blow up doll on holiday lol)
skin1235,
May 6, 6:05pm
well not 50 times day anyway, after twice you're just a skite
I reckon chas has got it pretty close, carry 2 bottles just in case she deflates
skin1235,
May 6, 6:10pm
the 'cover' you mention will need to be very robust meds, 5psi in an uncontrolled tube burst will scare the shite out of you, and 10psi will take some serious containing. thats 10psi ( pounds per square inch ) pressure trying very hard to breech your cover, a human jaw can barley develop 12 psi pressure, dogs can crush bones with their 19-25psi depending on breed and jaw length
10psi will need more than a bit of tarp with some rope etc, if the containing cover has 200sq inches of area 10psi is equivalent to a truckies tie down at 2000lb
the reason I say this - compressed air can kill, as many a tyre fitter knows, thats why they put them in safety frames, its not to contain them if we forget to unplug the compressor ( the frame will not contain them anyway when that happens ), its to stop the tyre killing you when it slips off the bead at 10 to 15 psi, it will bend the frame out of shape but at least not kill you
medcare,
May 6, 6:19pm
deflates.? Is that like the same as going down on me. ? ha ha.
medcare,
May 6, 6:22pm
I once had a trailer tire burst when pumping it to 60PSI, it was rated to 75PSI but exploded at 65, my head was down at the valve pumping away.
Hmmmm. Maybe that helps explains a few things.
skin1235,
May 6, 6:44pm
lol yep I knew you had lots of air meds, - but human lungs and muscles struggle to inflate beyond 5 psi, try it sometime, close your lips around a gauge end and blow your hardest many years ago, far too many years ago, when I was doing an apprenticeship as a mech, there was a pic doing the rounds of a guy who was standing on a truck rim to hold the 3rd ring in place, the next pic was a starfish shaped hole in the roof ( general procedure was you put your foot on the 3rd ring to hold it in the claw until the air pressure in the tyre built up to about 10psi, after that there was nothing that could shift it from the claw, we often gave them a good smack with a large hammer to make sure they were seated in the claw properly - if they weren't they would snap into place with enough noise to make your ears ring for a while - and that was at 10 psi or less you know the mag wheels they fit to trucks today?, they're pretty robust eh
they are rated for an absolute destructive max of 150psi, after that the rim will probably explode, most are only inflated to about 65psi, larger tyre are less
medcare,
May 6, 7:03pm
A trumpet player blows up to +1.9 psi when making staccato high notes[.
Healthy humans can blow up to 2.5 psi for very short periods of time, any higher pressure or longer time and you can tear alveoli and develop pulmonary lung bleeding.
medcare,
May 6, 7:14pm
Anyway my inflated tube application. Which is still in the theoretical stage is something like this.
There is a device that weighs 100kg, it sits 30mm off a flat surface (on 4 corner legs) it has a flat bottom plate, surface area 500mm by 500mm.
On a regular basis I need to lift the device 300mm.
For various reasons there is no ability to use any form of hoist or leverage, I simply need to vertically dead lift the 100kg device 300mm.
The idea is to slide a deflated tube, in a canvas cover, no more than 30mm high under the device, then inflate and lift it.
My actual lifting pressure calculations based on the surface area of both the inflating tube and the flat bottom of the device was actually more around the 1-2 psi, however I thought to inflate it to 10 psi to ensure the tube was solid and did not overly flex or bend.
But in hindsight I might be dreaming at 10 psi, and maybe 5 psi will be steady and stable enough.
medcare,
May 6, 7:41pm
Chas, I agree with skin that your calculations are in the ballpark so would you mind running the numbers for me again,.
What volume of air is required to inflate the dead flat (empty) tube to 5 psi, to the dimensions in the attàched link.
AND the reason for the 50 lifts is that there are 25 of these 100kg devices and they may each get lifted twice a month, so I want to carry sufficient air to do a months worth of lifting. And also I have thought of a basic AC air pump, OR even a foot air matress pump, but again for a range of reasons this is not a preferred option. Thanks :-)
medcare,
May 6, 7:56pm
Yep I thought about the vehicle exhaust jacks, main problem is that they are just too big and cumbersome, most of them are 650mm diameter and I'm heavily restricted by the 500mm x 500mm base, no room for overhang. Cheers
Ah but you missed the 2 moot points. 1 vehicle acess. 2 vehicle as air power. Anyone who has ever ripped a spark plug outa an old petrol fergie and fitted a cylnder air pump and pumped up a tire. And dive cylnders are like twin sets 51 or so cube and then old 71 cube and 88 cube 88 would do it
medcare,
May 6, 8:23pm
Vehicle access could be an issue, given some of these devices are on the 2nd floor lol.
I already have 6 medium sized 16 litre Catalina dive bottles, they weigh roughly 9kg. But are generally to big to use as a range of other equipment is carried so I'm thinking more of a small compressed air bottle slung over the shoulder. I haven't yet built the tube in a bag device, so I havnt filled it with air to measure the volume or stability, this is just at the theoretical stage.
But my maths ain't what it used to be, and I didn't want to put it all together then find I still need to lug big air bottles around. So I thought I'd work out the air volume first.
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