tank fill rate

[nadwidny]

It's not just PSI - it's also a recommendation from a number of agencies (TDI, PADI) with respect to blending technique.

Slow fills for O2 prevent compression heating (adiabatic compression) that could result in ignition. The lower the concentration of oxygen - the lower the risk of igniting hydrocarbons or seals in the system. Hence the faster fill rates for lower fractions of O2.

But that is a qualitative argument. And no, I have not seen a quantitative argument to why 60 for O2 is better than 40 or not as good as 100.

I know the theory. I was hoping for some insight into why those specific rates are recommended.

 

[rjack321]

In its Fill Station Operator Hazmat training, PSI recommends filling air at 300-600 psi/min, nitrox at 200 psi/min, oxygen at 60 psi/min.

the 60psi is comparable to what's in oxyhacker.
the other two I have now idea what the basis might be or why <40% nitrox need be any different from air.

Most banked nitrox operations go a lot faster than 200psi min.

 

[Compressor]

I have a LDS that ca do a 30 second fill.

OMG. That is insane!!

 

[cool_hardware52]

The gas temperatures you get from compression heating are considerable - approaching 700 degrees F. Not good for the cylinder. And when it cools - you'll loose 15% of the pressure (e.g. 3000 hot may cool to 2600). Not a good practice.

Are you claiming the tank will reach 700F? If so look for burned Off VIP stickers, melted valve seats, and melted tank neck orings......

This of course does not happen.

The temperature rise seen is well below the tempering temps for steel, and the added thermal mass of aluminum cylinders and greater conductivity means al bottles won't get very hot either.

Are fast fills a bad idea? Yes for several reasons. Damaging tanks via overheating isn't one of them.

Tobin

 

[bl6394]

Are you claiming the tank will reach 700F? If so look for burned Off VIP stickers, melted valve seats, and melted tank neck orings......

This of course does not happen.

The temperature rise seen is well below the tempering temps for steel, and the added thermal mass of aluminum cylinders and greater conductivity means al bottles won't get very hot either.

Are fast fills a bad idea? Yes for several reasons. Damaging tanks via overheating isn't one of them.

Tobin

Tobin - reread the post...

The GAS reaches a theoretical temperature of approximately 700F - based upon adiabatic compression. The total temperature of the entire system will raise based upon the heat (energy) being distributed throughout all of the components of the system. The primary concern for a filler is ignition when any contamination exists in the valve / tank - in an oxygen rich environment. A secondary concern is the stress on the cylinder resulting from unnecessarily rapidly filling the container.

The source of this statement is the TDI Advanced Gas Blender manual. But if you want - we could derive the answer - by looking at bringing a gas from 0 psi to 3000 psi instantaneously in an container of fixed volume.

And for another point of view on fast filling cylinders - please visit the following PSI link. PSI-PCI - Fast Fill, Slow Fill, Does It Make A Difference?

Fast fills are not a smart practice for a variety of reasons - including shortening the expected life of the cylinder.

 

[bl6394]

OMG. That is insane!!

I dealt with a fillstation operator like this here in the midwest this weekend...

LP108's cleaned for oxygen service with a working pressure of 2640 (plus rated 2400's) - rapidly filled in 30 seconds. The pressure in the cylinders was 1800 after it cooled.

I asked the guy - "these cylinders are cleaned for oxygen service - is your fill station supplying modified grade E air?" He looks at me with a confused look and says - "this is an expensive compressor - we test it once a year! (4 times a year is industry standard). And what kinda weird valve is this with a screw-in!"

I'll be O2 cleaning these cylinders before I partial pressure blend again.

Not saying I'm better than this fill station operator - just better trained.

 

[cool_hardware52]

Tobin - reread the post...

I did, you referenced only temperature

The gas temperatures you get from compression heating are considerable - approaching 700 degrees F. Not good for the cylinder.

And for another point of view on fast filling cylinders - please visit the following PSI link. PSI-PCI - Fast Fill, Slow Fill, Does It Make A Difference?

http://www.psicylinders.com/inspectors/library/29-fast-fill-slow-fill-does-it-make-a-difference

Your link is for SCBA tanks, i.e. hoop wrapped cylinders, not scuba tanks.

Fast fills are not a smart practice for a variety of reasons

Agreed

- including shortening the expected life of the cylinder.

Hoop wrapped SCBA maybe, scuba unlikely, scuba due to compressive heating of the tank? Good luck with that one.

The lower end of the tempering range for 4130 is 750F, solution aging temps for 6061 alloys are typically north of 500C / ~900F

Tobin[/QUOTE]

 

[bl6394]

I did, you referenced only temperature

[/QUOTE]
Gah! Look at the quote you just put up there. Note the two key words "... gas temperatures ..."

Not sure how I could have made this any clearer for you. I'm not going to exhaustively review Luxfer's mfg recommendations, nor PST's recommendations. Nor will I review the Ideal Gas law with you.

Just take some time and give it some thought.

Cheers.

 

[cool_hardware52]

Gah! Look at the quote you just put up there. Note the two key words "... gas temperatures ..."

Not sure how I could have made this any clearer for you. I'm not going to exhaustively review Luxfer's mfg recommendations, nor PST's recommendations. Nor will I review the Ideal Gas law with you.

Just take some time and give it some thought.

Cheers.[/QUOTE]

LOL,

So your intent was to convey something other than 700 degree gas is "not good" for the cylinder?

Again,your words:

The gas temperatures you get from compression heating are considerable - approaching 700 degrees F. Not good for the cylinder.

Tobin

 

[rjack321]

And for another point of view on fast filling cylinders - please visit the following PSI link. PSI-PCI - Fast Fill, Slow Fill, Does It Make A Difference?
.

PSI cracks me up. On the one hand they boast about the safety record of 6351 aluminum cylinders and how VIPs and VEs have reduced their failure rate to zero. And only like 12 ever burst at all anyway (a huge underestimate). Then when it suits them they say stuff like this: "Since 90 percent of cylinder failures occur during the fill process and, every year numerous cylinders of various designs rupture, great care should be given to ensure the cylinders are not damaged."

Oh and they aren't metalurgists or engineers either.