Dedicated Nitrox Tanks

[STITCH]

I have a question. I was checking out a Nirtox training manual and read something that got me wondering. The book says that you need to dedicate a tank/tanks to Nitrox only. Why is that?

 

[scarefaceDM]

Deadicating a set of tanks for Nitrox only depends on a constant factor. Do you get fills from the same shop with a Good air station?

The reason for that is because some shops may not have a - high quality of air, thus contaminating an O2 tank.

I have Nitrox tanks and get my fills from two different LDS that have a higher HEPPA system ( 3 -4 filters )which translates to CLEAN Air. So I am not worried about contaminated air to screw up my O2 cleaned tanks.

However. On the safe side. I also have two alu 80 for air only. BUT I always get fills from a LDS that has a minimum of Three filters.

The question remains, if you get fills from various dive shops, then I would have dedicated Nitrox tanks only and regular Air tanks. Each shop, unless you can see the Air system may not have the BEST quality of air, thus can contaminate a O2 cleaned tank. which results in more cost to you for a new O2 cleaning. But remember a dive shop which does not maintain there compressor nor change filters..on a regular basis may have contained air. Always ask to see the maintance chart to see when they change filters last. Especially if it is a dive shop you never been before.

Just an FYI

Stephen

 

[matt_unique]

I have a question. I was checking out a Nirtox training manual and read something that got me wondering. The book says that you need to dedicate a tank/tanks to Nitrox only. Why is that?

Kinda sorta is the short answer....it depends on a few things. The way the shop mixes nitrox and the 02% you get.

If your shop does "partial pressure" mixing then you need an 02 cleaned tank. This means they pump pure 02 into your tank then top it off with "clean air" to get the desired 02%.

If you get 02% higher than 40%, regardless of the way it's mixed, you need an 02 cleaned tank.

If you get premixed nitrox less than 40% you don't need an 02 cleaned tank.

Once you get a tank 02 cleaned, you can't get a regular air fill without voiding the 02 clean status unless it is specifically filled with "clean air". Clean air is air you get through special filtration systems used with partial pressure nitrox mixing.

--Matt

 

[scubawally]

ok here it is in laymans terms. There are 3 ways that modern dive shops use to make nitrox available to customers.

The first method and the most prevailent method used to day is partial pressure blending. To do this they first drain your tank (not all the time but most of the time) add a certain amount of pure O2 to your tank and then top it up with hyperpure air. In order to do this you have to have your tank and valves O2 cleaned. This will insure a very low levels of hydrocarbons within the tank. This is essential because if the tanks contain hydrocarbons and were then allowed to be filled with pure O2 under pressure there is a fire/explosion risk. In order to find out how much O2 needs to be added to the tank the blender inputs the size of the tank, working pressure, and final O2 concentration into a gas blending program and the program spits out a number....that number is the pressure of O2 that must be inside of the tank after the initial O2 addition. The blender then simply fills the tank to its working pressure with O2 clean (hyperpure) air. This math can also be conducted on paper however the blending software is not expensive therefore it is commonly used.

secondly for recreational nitrox mixes the shop may invest in a membrne system that is used in conjunction with there compressor that is used to filter out a little bit of the nitrogen that flows into your tank. In this situation the blender simply 'dials in' the requires O2 percentage and then uses it to fill your tanks. In this mothod no pure O2 is ever added to your tank and thus they do not have to be O2 clean.

The third method used is essential the same as the partial prussue blending method. In this case the dive shop will premix nitrox usually about 40% in bank cylinders. These cylinders have to be O2 clean as pure O2 is added to them in oder to mix the nitrox contained within them. The shop owner then transfers the nitrox (@40%) into your tank. If you desire EAN40 this is all they have to do. If you with another nitrox blend such as EAN32 they just use the same gas blending software mentioned earlier and add so much premix to your tanks and then either top up with hyperpure air or just regular air. In this instance as well your tanks do not have to be O2 clean as pure O2 never eners your tanks.

It is to be noted that high EAN mixes still have to be blended using the partial pressure method.

also once you get a tank O2 cleaned you can then no longer get it filled with regular air. You need to fill it with O2 clean air (A.K.A. hyperpure air, or oxygen servicable air) unless you are prepaired to get the tanks O2 cleaned prior to your next partial pressure blended nitrox fill.

just so i dont have to write this later the membrane system that some shops use is Very Very expensive (i have the figure of around 16k for some reason) and thus unless the shop deals with alot of nitrox users then it is most likelyto use the partial prussure blending method


thanks

 

[scubawally]

thanks matt

i guess we were typing at the same time and your response just posed first....very well said and it sumarized what I wrote very well....but you still get the credit as yours posted first

thanks

 

[Jimmer]

I'm fortunate in the my primary LDS owner is a HVAC tech by trade and takes incredible care with his compressor and filters, my air fills are the same air that he puts on top of the O2 when mixing Nitrox, so I have nothing to worry about. The other two shops I occassionally get fills from are big tech shops, so their air is all "O2" clean as well. Like the other guys have said, you only have to worry about it if the shop you're getting an air fill from, doesn't use O2 compatible air.

 

[scubawally]

thats not so much true you have to worry about it if the shop you are getting your fills from uses the partial pressure blending method....unless of course you get all of your tanks O2 cleaned

 

[pescador775]

Method number four, which is used by many who stir up a batch of home brew NITROX, is the continuous flow blending. Briefly, the compressor inlet is connected with tubing to the bottom of an open ended pipe which is stuffed with metal ribbon or baffles. Oxygen if fed into the pipe at a location a few inches below the open end (top). As the compressor inhales from the pipe the oxygen mixes with air to form a mixture or "blend". The oxygen percentage is read by an analyzer at the bottom of the pipe. The compressor pumps the selected mixture, like 36% O2, into the dive tank. No special "dedication" is required for the tank, especially if is a new tank and valve which are O2 clean from the factory. Almost all are. For older tanks, the real danger is the valve which has been lubed with silicone. Those things will react to high oxygen, above 50%, and can go bang or catch fire. As an aside, most modern compressors pump air or gas which is relatively clean and will not present a hazard if the tank is also used to contain oxygen. However, as a precaution, when using a well maintained compressor for this purpose, it is advisable to re-clean the valve and tank at regular intervals. It is difficult to say how often and that is a technical area beyond what you are requesting in your original post.

 

[Jimmer]

thats not so much true you have to worry about it if the shop you are getting your fills from uses the partial pressure blending method....unless of course you get all of your tanks O2 cleaned

That's all these guys use. None of them preblend, I know the owners of all 3, and my personal LDS I'm working with them on my divemaster, so they're teaching me to do my own Nitrox mixing, which is a very cool plus.