Liquid oxygen

[Russ88]

In liquid oxygen containers for home breathing assistance:

1.  If one leaks a little bit, does using it first make more efficient use of the oxygen?  As in opening the valve to allow it to feed through the hose relieves pressure at the leak, so less is lost?

2.  What is the ratio between the volume of liquid liters of O2 and gaseous liters?  Assuming the temperature and pressure inside the container at the minimum required to keep it liquid.

[Peter Pedant]

Hi Russ - are you in the UK? We dont have home liquid oxygen. is the cylinder black with white shoulders?

The oxygen is compressed and follows Boyles law. Home supply is usually an E cylinder in size because the others are so heavy. Your first question is so garbled I cant understand it.

Q2 - straight boyles law, at constant temperature. All commercial oxygen cylnders are pressurised to a certain pressure - 2500 atm I think and the E cylnder when expanded is 7500 litres. I think - I'm sorry I just dont carry around these figures in my head.

[kempie]

This page addresses your second question.

[Russ88]

Peter, I'm in the US.  Note that I asked about liquid oxygen, not compressed.  I think it would have been absolutely amazing if you had those figures in your head.

 

Kempie.  Thanks for the link.  That answered my question number 2.

 

I still hope somebody can make sense of my "garbled" question 1 and tell me the physics of the question.

[Russ88]

On rereading my question, I see how it might not be understood.  I have two containers.  One does not leak.  One does.  When I use the one that leaks, does the fact that the valve is open, allowing oxygen to escape to its proper use relieve the pressure so that none or less is lost to the leak?  Or, does the overall pressure stay the same, allowing both the proper use and the leak to occur?

Still not sure this is understandable, if not, nothing lost in trying.... 

Maybe I could instead enter into a discussion with the friendly pedant concerning the definition of garbled....

[Peter Pedant]

hi me again. None of us have lox here in the UK - I am absolutely gobsmacked, it is available for home use elsewhere. Storing it is such a bl++dy run-around.

The site for Q2 is OK - i think you could usefully email the owner of the site who clearly is on home oxygen himself. I find it very hard to follow as none of my physics has been foot-pound-sec. Home oxygen in the UK is all (or was all when I last looked) molybdenum steel cylinders which are much stronger and therefore have higher filling pressures and higher expanded volumes. No-one carried them around, as the tare-weight is much heavier (8-10kg I think)

good luck - I've re-read Q1 and I still cant understand it.

[BillyBB]

Rate of flow will be higher the greater pressure differential. If it's liquid oxygen the pressure might not change that much from full to empty, I do not know.

Having a leaking oxygen cylinder in the house is a recipe for disaster, very dangerous.

[jake-the-peg]

This is incredible - I didn't believe you at first now I've looked at some web sites and people are actually using reservoirs of LOX for home breating in the US.

This stuff is quite literally rocket fuel. When I worked in the UK Atomic Energy Authority there was a blanket ban on this stuff on our site. Just too dangerous.

I hate to think what this does to your home premiums!

As to the question - it rather depends on whether by using the oxygen you reduce the pressure differential but I doubt it would make much difference.

But LOX is not something to take lightly if you have a leak I strongly urge you to get it fixed as soon as humanly possible. 

[Russ88]

Thank you all for your responses. 

I appreciate the concern posted regarding potential danger, and would like to explain that this container leaks at a rate of maybe half a liter per day.  This in an open, ventilated area away from flames, etc.  This makes an insignificant increase in the amount of oxygen already present in the air.  The companies that provide oxygen have a training session and make all users very aware of safety concerns.  

I would say that oxygen is NOT a fuel, rocket or otherwise.  It is oxygen which, yes, when combined with a fuel makes for fire, but that is why I and other users take great care in its use.

Thanks again to all for your posts, particularly Kempie.

[Russ88]

I forgot to add that the offending leaking container will be replaced tomorrow.

Thanks again to all of you.

[Peter Pedant]

Why did you go to the internet before getting the container replaced? I am just interested to know.

jake the peg I was similarly pop-eyed when I realised that Russ WAS talking about home lox.

It has certainly motivated me to go and look at an industrial plant: there has to be a pop-off valve for hot days and low use, and what they do for leaks.

Good luck with your new container Russ - and your home o2 therapy.

[Russ88]

Peter,

I didn't go to the internet before deciding to replace the container.  It was scheduled for replacement.  The provider comes every two weeks, and replaces containers as needed.  The whole question was just kind of an intellectual exercise, one (except for getting my answer to question 2) I now regret.

As often happens on these kinds of forums, the discussion leads itself away from the original point.  I am absolutely aware of potential dangers of very high levels of oxygen.  As I said in my last post, this leak is at such a low level, there is virtually no increase in the percentage of oxygen in the ambient air in my house.

Thank you again for your responses.