Industrial Tank Fills for Air

[broncobowsher]

I recall someone figuring it could be done. If you can get the really high pressure Nitrogen cylinders. I want to say the 7500 PSI? At that point you end up blending your own air, or at that point you might as well be making your own Nitrox. The industrial oxygen isn't that high of a pressure, but if you are partial pressure blending it you can get away with that.
Would not make sense is the gas prices are high. Also not for filling a single tank every once in a while. And most every other scenario. But under just the right conditions it might be possible to affordably do it.

But the local fire department is probably a better option, even if you end up buying a box of doughnuts for them every once in a while.

 

[rx7diver]

... Really the solution for OP is not to rent cylinders, but to buy a compressor.

Alternately, the OP could own enough scuba cylinders so that he/she would not be too inconvenienced when leaving a few of them awhile at the remote LDS, to be picked up at some later, more convenient time.

For example, if the OP typically uses two (say) cylinders during a weekend tune-up dive and gear check at his local lake, he might own four cylinders (so that he could leave two of them awhile at the remote LDS to be filled). Even though he would have the expense of four (annual) VIP's and four hydro's (every five years), this would be much less expensive (I'm guessing) than purchasing and maintaining a scuba compressor. And he can always sell the extra cylinders easily enough, without too much loss, if/when he decides to.

I would recommend purchasing an equalizing whip, too, for this approach.

rx7diver

 

[rjack321]

Not sure I agree with this as a general statement. A source can say they have breathing air with contamination below maximum allowable levels. But at 5 ATMs of pressure, those same contamination levels would be 5 times higher, and may no longer be within tolerance. That's what I meant by SCUBA quality air. Effectively, whatever air they have would have to have contamination that's <20% maximum allowable levels if going to maximum recreational depths.

CGA specs both a grade E and a grade D breathing air. D is/was for surface use only. Those specs were written decades and decades ago.

In actual practice, you will not find a "lower quality surface use only breathing air" anywhere, there is zero market for grade D air.

 

[SpeedyJ]

CGA specs both a grade E and a grade D breathing air. D is/was for surface use only. Those specs were written decades and decades ago.

In actual practice, you will not find a "lower quality surface use only breathing air" anywhere, there is zero market for grade D air.

I went through this with my gas supplier when setting up my garage trimix fill station. The common breathing air cylinders were Grade D, though I could get Grade E brought in. My guess is that the market is actually mainly Grade D, though it's likely pure enough to meet Grade E +.

In the end it was cheaper for me to buy some bank cylinders and run them to the dive shop.

 

[rjack321]

I went through this with my gas supplier when setting up my garage trimix fill station. The common breathing air cylinders were Grade D, though I could get Grade E brought in. My guess is that the market is actually mainly Grade D, though it's likely pure enough to meet Grade E +.

In the end it was cheaper for me to buy some bank cylinders and run them to the dive shop.

They may spec the air at D but it's not like they use a lessor quality filter to make it. If brought for analysis at a gas lab I would be shocked if it didn't meet E. It's the same thing with O2 and helium. Industrial O2 isn't "dirtier" than any other grade just less thoroughly documented. Ditto 5 nines helium vs UHP

 

[nadwidny]

I went through this with my gas supplier when setting up my garage trimix fill station. The common breathing air cylinders were Grade D, though I could get Grade E brought in. My guess is that the market is actually mainly Grade D, though it's likely pure enough to meet Grade E +.

In the end it was cheaper for me to buy some bank cylinders and run them to the dive shop.

Grade D is a garbage spec. I can meet that with my bicycle pump.

 

[nadwidny]

I recall someone figuring it could be done. If you can get the really high pressure Nitrogen cylinders. I want to say the 7500 PSI? At that point you end up blending your own air, or at that point you might as well be making your own Nitrox. The industrial oxygen isn't that high of a pressure, but if you are partial pressure blending it you can get away with that.
Would not make sense is the gas prices are high. Also not for filling a single tank every once in a while. And most every other scenario. But under just the right conditions it might be possible to affordably do it.

But the local fire department is probably a better option, even if you end up buying a box of doughnuts for them every once in a while.

I know of at least 2 examples where a commercial outfit was selling a 21% O2/N2 mix by combining O2 and N2 and selling it as air where the end user either passed out or died. Relatively recently.

Edit- Both were hypoxic. One of the mixes was 100% nitrogen. The other was something like 5% O2.

 

[SpeedyJ]

They may spec the air at D but it's not like they use a lessor quality filter to make it. If brought for analysis at a gas lab I would be shocked if it didn't meet E. It's the same thing with O2 and helium. Industrial O2 isn't "dirtier" than any other grade just less thoroughly documented. Ditto 5 nines helium vs UHP

There is no guarantee the cylinders are coming from the same source, and I know for a fact at the supplier I was using that Grade D was filled on-site while Grade E was shipped in. Could their compressor have been putting out Grade E+ breathing air, sure, but they didn’t have the paperwork to prove it.

I’ve gone back and forth on using industrial gasses vs UHP, but having multiple cylinders of helium from a major national supplier that had low ppm CO in them while still being within spec, I’ve made the decision to spend the extra $50 on UHP. The UHP comes with cylinder analysis and a 1ppm CO limit. This is less of a concern for people who are running a blending stick and a compressor where the hopcalite takes care of it.

 

[iliketopetsharks]

I know of at least 2 examples where a commercial outfit was selling a 21% O2/N2 mix by combining O2 and N2 and selling it as air where the end user either passed out or died. Relatively recently.

Edit- Both were hypoxic. One of the mixes was 100% nitrogen. The other was something like 5% O2.

Yikes. It's crazy to me how many people still don't analyze their gasses.

 

[SpeedyJ]

Yikes. It's crazy to me how many people still don't analyze their gasses.

I don't think many divers have an appreciation for just how easy it is to make a mistake while blending gasses. A moments inattention due to a text message, an interruption from a customer, or a quick step away to grab a drink can throw everything off.

I added a big whiteboard to my blending setup this year so I can write out the gas math and check off each component being filled. With a mess of tanks all needing different gasses at different pressures, its been a big help to keep me on track during extended blending sessions.