OT: Gas Cylinder Storage Capacity vs. Pressure

[Paul]

For a liquified gas, the heat absorption characteristics of the side of the tank, change as you go from the liquid portion of the tank, to the vapour portion of the tank. In some cases, for an outdoor tank, in relatively cold winter conditions, there may be a condensation pattern on the tank which hints at the content. So you don't even need a liquid crystal strip. For an outdoor tank, the ambient temp could be so low, that there is no vapour pressure to speak of and you can't run your combustion device off it. Even though it is full. In warmer weather, perhaps this strip and a procedure, helps determine fill.

You can also use an ultrasonic instrument, to measure what is in the tank. This uses a gel applied to the tank, to enhance coupling of ultrasonic energy from the transducer, to the tank. The sentence at the bottom indicates that perhaps this application is for a ship-borne CO2 extinguisher system. This is a lot like an ultrasound.

Dry nitrogen or oxygen, remains a gas at the 3000 PSI it ships at.

80 liter cylinder is how I heard it described in the lab, for the cylinders that sit next to instruments such as a GC. Our GC had a tank of argon. Dry nitrogen by comparison, is a lot cheaper. Oxygen for a ParBomb, is only usable if it can pressurize the bomb. If the bomb runs at 25 bar, you need at least 25 bar in the tank to charge it. 80 liter cylinders, should always be restrained to the lab bench. When fitting the regulator, you use teflon tape on the threads. That was the first safety lecture I received at work, was about cylinder safety.

You can leave a little gas in an 80 liter, so that nothing untoward gets into the cylinder, when you return it. The gas supplier vacuums the tank upon receipt, before refilling.

The highest pressure gas I know of, is hydrogen at 10000 PSI. The tank may be filled with a zeolite, to control the rate of flow out of the tank. This will distort any convoluted maths about gas laws. I don't know how you would determine what is left in one of those. Never worked with any. Hydrogen is the only gas that is exothermic as it leaves the valve. This means, if you crack the valve on hydrogen, it is self-igniting. CO2 on the other hand, "snow" shoots out when the gas leaves, as it is endothermic.

Some gases can polymerize in a tank, which is how teflon was discovered. Plunkett was weighing his bottle, when the discrepancy was detected.

"As Plunkett attempted to make a new chlorofluorocarbon refrigerant, the tetrafluoroethylene gas in its pressure bottle stopped flowing before the bottle's weight had dropped to the point signaling "empty".

Since Plunkett was measuring the amount of gas used by weighing the bottle, he became curious as to the source of the weight, and finally resorted to sawing the bottle apart. He found the bottle's interior coated with a waxy white material that was oddly slippery.

Analysis showed that it was polymerized perfluoroethylene, with the iron from the inside of the container having acted as a catalyst at high pressure."

Paul

[Cursitor Doom]

You seem remarkably well-informed on this subject and your lengthy reply deserves a follow-up. There are two gases I'm mostly concerned about here: nitrogen (primarily) and ultra-pure hydrogen (not so important in this context). The cylinders are pretty heavy (about

80-90kg) so right at the top end of handle-a-biliity for one bloke of my vast age. HTH and thanks.

[Cursitor Doom]

Does that mean:

a) I'm being screwed over by British Oxygen?

b) I can't use it to treat any pre-cancerous lesions I may acquire from too much sun exposure in the future?

The cylinder seems incredibly thick and heavy just for just "pressurised gas"!

[Max Demian]

The cylinder needs to have a thick wall *because* it's just "pressurised gas". The more you put in the higher the pressure, unlike gasses which liquefy on compression which are at the vapour pressure of the liquid/gas at the current temperature.

[Tim+]

The tare weight is stamped on a sheet metal disk around the neck of the valve on propane/butane cylinders. Probably for other liquid gasses too. Have a Google for the units used. I seem to recall that it’s something weird like decimal pounds.

Tim

[Tim+]

It’s such a shame no one has thought of creating a publicly accessible network of computers that you can search for information. That could answer so many questions like this.

Tim

[Tim+]

Liquid gas (depending on the gas) will be at much lower pressure. So, no surprise that cylinders of gaseous gases need to be stronger.

Tim

[zall]

Acetylene is different, it is solved in acetone in the cylinders.

[SteveW]

I don't know what size bottle you've got, but we used to get Nitrogen bottles, about 5' high and less than 1' across, pressurised to about 200 Bar (2900 psi).

[Rod Speed]

Not Acetylene, it's dissolved in acetone in the cylinder.

[SteveW]

Both of those will be gas only, with no liquid and so pressure *is* a good measure of remaining quantity.

[Rod Speed]

The pressure is fine.

I did.

[Brian]

Sounds like you are doing welding and cutting etc, so different applications to my area which is centred around LPG, in my case for my motorhome. My knowledge is based on research done when faced with essentially the same problem as you- how much do I have?

[ajh]

Yes missed that , that's why it's called dissolved acetylene

[Andy Burns]

I thought all caravanners had a spring balance to weigh their gas bottles?

[Paul]

I don't think that's entirely fair.

Not all the practical details of working with gases, are in a handy form for consumption. Sure, you might have had PV=nRT in school, but it does not mean anything unless you had labs with gases for the experience. Which is normally lacking.

Most of the good experience with gases, comes during your apprenticeship. When the guy with one arm, explains what not to do :-)

Paul

[Brian]

Some do. I use one of those luggage scales - essentially an electronic spring balance.

These days, there are lots of gizmos for motorhomes / caravans, including to tell you how much gas you have. Motorhomes/ caravans are quite sophisticated - decent heating, mine has a system similar to Hive so I can control it remotely, showers, microwaves, …..

[Max Demian]

"Gaseous gases" eh? (They used to call them "permanent gases".)

[Colin Bignell]

In days long past, when I used to go camping, Camping Gaz supplied a spring balance specifically for their bottles showing quantity, rather than weight.

[Tim+]

Given that Camping Gaz etc is sold by weight, I think quantity = weight (minus tare).

Tim