Filling o2 tanks

[DonMuncy]

17 minutes ago, DrBill said:

I got my big O2 tank on Craigslist for $25. Then bought transfill adapter.  I only use one tank since it's only c $20 to swap with a full one. For a bilt in tank, I might get 2 and swap them about.

Bill

 

You did well.

[Yooper Rocketman]

I guess I didn't realize how good I have it.  I haul a full O2 tank from the rack in our fabrication shop, top off the system and then haul it back and the guys can't even tell I used any from it.  Since we go through several tanks a week, I always have a fresh "full" tank every time I need to top off. The only pain is hauling it.  I did have a two tank cascade system at one time, but when use went down it didn't make sense to tie up two bottles in my rental agreement for just that.

Tom

[peevee]

Here's a question: how does one purge the tank after someone left the switch on and it's been allowed to breathe in atmosphere? The poh warns against it, but it happens... 

[N201MKTurbo]

Ideally you would suck all the air out with a vacuum pump and then backfill with oxygen. If you fill it to a hundred pounds or so and then let it out a few times, you will be ok. 

The big hazard is moisture in the system that can freeze the regulator. Either way the risk is low.

[carusoam]

Purging is done by the guy filling the tank.  Put some O2 in, drain it out, put more in, drain it out....repeat a few times...

Having some nitrogen In the system isn't going to be very hazardous...

It is possible, that they can measure %O2 with a sort of expensive sensor.

As far as draining gasses from the system...  it all leaves as it flows out from high pressure to low....

PP advice only, not a commercial gas supplier...

Best regards,

-a-

[peevee]

9 hours ago, N201MKTurbo said:

Ideally you would suck all the air out with a vacuum pump and then backfill with oxygen. If you fill it to a hundred pounds or so and then let it out a few times, you will be ok. 

The big hazard is moisture in the system that can freeze the regulator. Either way the risk is low.

Oh, I have a vac pump for ac purposes. If I can make the fittings work out that'd be easy, didn't think of that. 

It probably won't take much  vacuum before the Scott fittings start to open though. 

[carusoam]

PV,

The light just came on...  It is difficult to take a built in O2 system to the refill station to get purged out..?

It may be slightly easier to fill some, drain, fill some, and drain...

Than it is to vacuum out what is in there.  

What are the risks for this...

1) moisture

2) other contaminants, other gasses like air...

3) other contaminants, dirt particles

4) Goofing up the vacuum procedure could allow some other unknown things to get sucked back into the system.  Some vacuum pumps use a special oil as a lubricant.  Keeping oil away from your O2 system would be extra important...

 

After this much thought, on different ways to cause a problem, I would think there is a procedure that is outlined by the people that build the O2 system..?

A chemist once showed me how he rinsed his coffee pot.  He added a small amount (not filling the whole thing) of water to the empty pot, swirled it around and emptied it. Repeated that procedure two more times...  essentially anything sticking to the side of the glass walls was being reduced with each rinse... theoretically his concentration of unwanted coffee particles was being cut exponentially with each rinse...

The chemist didn't use a vacuum to dry the coffee pot.  He could have. He just found a simple usable way to reliably perform the same task...

Find a way to add a small amount of pure, dry, O2, swirl it around, and dump it down the drain.  Repeat a couple of times...

I was reminded about how much a small amount is with regards to O2 tanks. One atmosphere is 14.7psi (from memory) or roughly 15 psi... a full tank is a bit over 1,500 psi... that is a hundred atmospheres...

Is there any guidance to follow for the first time using the O2 system after maintenance?

PP ideas, not a CFI or mechanic... not making any recommendations, just trying to stir some thoughts...

Best regards,

-a-

[DonMuncy]

What gases and contaminants  get into the tanks. Are they the same ones that are in the air that we breathe all the time.

What happens if you have even a whole tank of "air" before you put oxygen in. Using the numbers previously quoted, you would wind up with a tank full of  99% oxygen and 1% air (if I am reading that hundred atmospheres correctly). Using a canula, what percentage O2 and air are you sucking in while on oxygen. Using a pulse oximeter, how much would you have to open the oxygen valve to account for that decrease in oxygen.

I am not advocating letting stuff get in your system that could harm the system, but we may be worrying a little too much. I have never read anything about problems with frozen regulators, but I'm willing to learn.

[N201MKTurbo]

A high pressure regulator has a tiny orifice with a rubber or teflon puck that pushes on it to stop the flow when the pressure in the output circuit is high enough. The pressure drop across this orifice can be 2000 PSI, this causes a big temperature drop in the gas. This is how air conditioning works. If there is any moisture in the gas it can freeze a plug in the tiny orifice. 

If it is warm enough, the plug will almost instantly melt. If your plane is near or below freezing, it won't melt. Up in the flight levels where you need the oxygen freezing temperatures are not rare. As you can see the conditions that would lead to a problem are rare, but $h!& happens....