Question on Filling Nitrox Tanks

[denisegg]

I have just purchased my own nitrox tanks last week from my LDS and picked them up and used them on my dive this past weekend. I live 100 miles from the nearest LDS so I either have to make a special trip to get air fills or do it when I am already making the trip for another purpose. This was the first time I had them refilled after I purchased them. When I asked to have them filled, he said I could not take them with me. He said they would have to sit at least 24 hours to get an accurate reading. They use the method of partial pressure blending where the o2 is put in first. This is very inconvenient for me because I live so far away. Is this standard practice?

 

[johntt1986]

from what i hear, is they blend as you add the rest of the gases to get your fill.

i cant speak from experience as i havent dived nitrox.

 

[scubawally]

this is common practice and the wait is to ensure hat hegasses are blended properly and you get the mix you wanted and not something too high in O2 for your planned depth.

 

[SteveAD]

It would probably be more accurate to say the shop needs 24 hours to get around to it. PP blending can be a somewhat time consuming and labor intensive process. It might not be in the shops best interest to tie up personel blending gas who are needed to wait on customers. The turbulence created within a tank during the filling process pretty much assures that the gas is mixed immediately.

 

[ScubaAndDreams]

I fill at home with my own fill station both nitrox and tmx...this is just another example of stupid self imposed dive shop rules. The reading (for nitrox) may vary by a % after 24hrs not much more..

 

[mike_s]

It would probably be more accurate to say the shop needs 24 hours to get around to it. PP blending can be a somewhat time consuming and labor intensive process. It might not be in the shops best interest to tie up personel blending gas who are needed to wait on customers. The turbulence created within a tank during the filling process pretty much assures that the gas is mixed immediately.

or it could be they only have one employee with the "math skills" to figure out how to get 32% or who knows how to run the fill equipment.



The math isn't that hard. For most mixes you could just make a chart up and put it on the wall. Doesn't even matter what volume tank it is... it's all based on PSI, not tank volume. I'm sure there is some chart out there you can download off the internet. I know there are mix calculators out there on the net.

I've never heard of a shop making you wait overnight to pick up a blended tank. I've gotten partial pressure fills, lets say 32%, they did the math, filled the tank and analyzed it and it read +/- 1% of what the math said, right after the tank filled. The next day it will be so close it won't matter.


If you had a 1/2 bucket of cold water and a 1/2 bucket of hot water, you pour them from one bucket to the other, you get warm water. The temp will be pretty equal over 99% of the bucket. You won't see much of a differnce with mixing gases. Analyze it a day later and it'll be within 1%.

I personally think your shop sounds a little clueless, either that or they had a lame excuse they told you because the person who knows how to do it wasn't there.


Just my 2psi worth.

 

[RoyN]

100 miles? :11: :11: :11:

 

[Mr Carcharodon]

I think the warm gas that results from the filling process may throw the oxygen readings off. And how far they are off may depend on how fast the fill was done. And with the potential for oxygen toxicity the shop may not want to risk sending you on your way with a bad reading. So to answer your question no what your shop is doing is not really that outside of the norm. It may be overly conservative to the point of being silly but some people will think the US tort system is silly, and others not.

Also know that no less an authoritative source than NOAA spend time telling people that they should roll tanks to promote gas mixing. That just seems remarkably absurd based on my limited knowledge of gas kinetics but then with the experts saying things like that it is no wonder that some people at the LDSs get confused.

 

[mike_s]

.

Also know that no less an authoritative source than NOAA spend time telling people that they should roll tanks to promote gas mixing. .

Don't tell the LDS that! They'll just try to charge her more now to "rank rolling"

 

[snepdiver]

I have personally witnessed customers at my lds standing there for 10-20 minutes while the employee filled the tanks and then the customer left with them.

I have solved your problem. Buy and move into and beach house across the street from a good dive shop in the panhandle. Then you will not have as far to drive and I have somewhere to stay.