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Discussion Starter · #1 ·
so what is the difference in weight of a 12lt twinset at 220bar at the start of the dive and at the end of the dive at 50 bar assuming all other variables remain the same
 

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aka Chimp 1 or Mavis...
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2.75kg for 230bar in single 12.

Regards
 

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The worlds slowest sailor.
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so what is the difference in weight of a 12lt twinset at 220bar at the start of the dive and at the end of the dive at 50 bar assuming all other variables remain the same
24 lts at 170 bar is 4.8kg
 

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Is there a foruma or is it just something you know?
 

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Air weights 1,225 kg m cubed so divide that by 1000 to get the weight of 1 litre then times by 24 then times by the pressure so around 6.5 kg and around 1.5 kg at 50 bar this will change if using any gas other than normal air
 

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aka Chimp 1 or Mavis...
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Discussion Starter · #11 ·
weight of air

Oh so I am going to be 5kg lighter at the end of dive? That 10lb I have to add to my weight belt? Bloody Hell I have 28lb on me now! Think it is because of compression of my 5.5mm divemaster suit.... :frown:
 

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The worlds slowest sailor.
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Oh so I am going to be 5kg lighter at the end of dive? That 10lb I have to add to my weight belt? Bloody Hell I have 28lb on me now! Think it is because of compression of my 5.5mm divemaster suit.... :frown:
the gas bit is around 6kg(14lbs).
in reality to go from single to twins its a lot less due to the weight of the extra kit.

do a weight check with near empty tanks-its the only way.
 

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What is it's fake mass
Fake Mass of Gas Is a new theory, bit like string theory only with moles.

It started when divers forgot there basic physics and stared double filtering.

Fake mass is forgetting that atmospheric air and BREATHING AIR are two different theories and that atmospheric AIR is measured differently for the pretty girl on the telly that tells you what the weather is going to be than for divers.

Thats called saturated vapour pressure density dewpoint. or blonds

The weight of air is dependant on if it is defined as air at 20oC (293.15 K, 68oF) and 1 atm ( 101.325 kN/m2, 101.325 kPa, 14.7 psia, 0 psig, 30 in Hg, 760 torr) and if so is called NTP Normal Temperature and Pressure in which case it is 1.205 kg/M3. NPT

As opposed to the engineering term NPT that stands for National Pipe thread used in big diving cylinders and bigger diving bells. But this is an American standard and so I should add that there STP standard ambient temperature and pressure is at 25C 77F

Or if we are talking about air at 0oC (273.15 K, 32oF) and 1 atm (101.325 kN/m2, 101.325 kPa, 14.7 psia, 0 psig, 30 in Hg, 760 torr)
in which case we call that Standard Temperature and Pressure STP

Or the chemical oil industry where STP in which case its 100 kPa and 14.504psi 0.986 ATA

Again unless we are taking about oil lubricated compressors that compressed this air and you wish me to identify the weight of the oil carry over from the poorly designed filters then STP is more probably the brand of oil additive you local dive used to fill said air cylinders.

Good practice is always to define the reference conditions fully or alternatively use the metric system and don't tell me at 15 °C (288.15 K; 59.00 °F) and 101.325kPa 1 ATA or 760 Torr.

Now what was the question……………..Oh yes

Air has some peculiar properties shared with most other gasses in that it contains moles or at least parts of them and should be measured only in cubic feet and that divided by 28.32 if you really really want it in litres

Most of us learn from school that a cubic foot of air as having the following parts.
Nitrogen (N2): 0.9864 moles
Oxygen (O2): 0.2653 moles

But forget the full family of moles being:
Argon (Ar): 0.01176 moles
Neon (Ne): 0.00002275 moles

Helium (He): 0.000006321 moles

Krypton (Kr): 0.000001264 moles

Xenon (Xe): 0.0000001138 moles
Hydrogen (H2): 0.0000006321 moles

Now you can add up all there molecular weights if you must and knock yourself out.

But the neat trick in the theory of gas itself in that 22.4 litres of ANY gas at STP. Any gas you care to mention on this planet or any other will contain exactly
6.02214199 x10^23 molecules of that said gas. And for the purposes of this post it does indeed include the planet Pluto, as a planet.

Now it would have been great if if they lowered the cubic foot to contain 22.4 litres than 28.32 litres but I guess an American foot size is different to a continental just as opposed to one foot being one sixth of a fathom than 0.166666667

It is called Avogadros number and it's he I guess who had the mole problem.

But that's good for us divers and bottle monkeys cos a singe mole of gas at STP will fill 22.4 litres

Or to make it easier ignore all the fancy gases that are used in lightbulbs and cars that run on water and just weigh what gas your left with without forgetting of course the water vapour and oil vapour but that I guess is just a minor mole hill to climb. :) Iain Middlebrook
 

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Nigel Hewitt
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I've been giving away my windoze gas blender program for years but one thing it does do is work out the mass of a fill for any mix.
One day I'll rewrite the help into something more current
 

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Ah, the old Iain is back:) I too had a mole problem, but in the end the doctor removed it. If a doctor did the same to the gas would it weigh less?:)

I use 0.0012kg per litre to calculate weight - it will get you close enough.
 

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Discussion Starter · #18 ·
Right ! Sorted ! Into eccy with 50 Bar and a bag full of lead then!
Thought I might end up doing that, just hoped (in vain )that the physics thingy might come to the rescue and save me a wodge of cash,never mind, mustn't grumble!
Eh Keith!
 

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All you have to do then is 'do the maths' to get from fresh water to sea water :) Nigels site might be able to help with this too:)
 

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Close enough!...................

Isn't that just typical of a scientist.

Someone innocently ask's to know the weight of something.
Then after a perfectly accurate engineered mathematical answer.

The scientists amongst us go for the "supermarket approach"

and round it up. :)
 
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