The way you are filling based on using multiple tanks one at a time is called a bottle cascade. It really helps to ensure that you get to use as much oxygen as possible. If you and your buddies are using this thing a lot, you may want to consider a booster pump. They allow you to basically drain the o2 tank all the way down without wasting any before you return it, and you don't have to worry about the whole cascade system. The most popular one for people filling their own tech rigs in SCUBA for closed circuit rebreathers is the Haskel Mini Booster Pump. You'll probably never break even on the oxygen cost vs the pump, but you'll be able to fill a lot more tanks without having to return the bottles, or having to lug around 3 of them to cascade them down.
Chris, great video and good information. The reason they call it aviators breathing oxygen, is because it has less moisture in it preventing freezing in the system at colder high altitudes. The oil/grease applies to all types of O2 used in welding/hospitals. It's been a really long time, but I think its .004% water vapor allowed to be called ABO, I think?
Interesting new tidbit for me re ABO having much less moisture than other O2 such as "medical" or industrial/welding O2. Thanks for your comment cadpipe.
It may have a lower spec, but it is irrelevant to the actual levels in the oxygen. All bottled oxygen has almost zero moisture and is extremely pure. The have to distill it from the atmosphere by cryogenically cooling it to almost absolute zero. Medical, aviation and welding oxygen are all filled from the same bank. The only difference is the labeling on the containers it is put in, and paper work. When it is used in a medical environment, they typically bubble it through water once it is brought back to ambient pressure to add moisture added back to it so it doesn't dry out your nasal passages. I have had this confirmed by multiple outfits that would fill O2, helium and argon tanks for us to partial pressure blend SCUBA tanks, as well as when taking PSI courses for doing visuals.
Hey Chris, nice video. I hope to be filling up my bravo soon. In my 201 I just use a portable 15L tank. If you ever make another video doing this I would really like to see how much each fill tank adds to the Mooney tank at each step. Thanks.
After filling the Mooney tank and supply tank will equilibrate pressures and that pressure will be less than the one the supply tank had originally. How much less is dependent on what the initial difference of pressures was between both tanks and also the relative size of the supply tank to the Mooney tank. Not that specific above, but one could take out pencil and paper and apply the formula PV = nRT to both tanks and figure out what the volumes exchanged will be and resulting final pressures as well.
Hello. How do you use all the O2 in each tank? The first tank did not empty completely. I assume it reaches an equilibrium so no gas moves in either direction. Will your tank empty only if the psi in your plane tank is below what is left in the supply tank? Also, how does one go about making a set up like yours? Can it be done with only 2 tanks? What is the approximate cost to make a set-up? Where do you get re-fills? Thanks in advance. Best regards, Stephen
Hi Stephen, It is practically impossible to use all the O2 in each supply tank since as you correctly assumed the supply tank and airplane tank reach an equilibrium where no flow occurs through the one way valve in the plane once the equilibrium is reached. The supply tank must start with a higher pressure in it than the tank in the plane for any flow to occur from supply to plane. It is also difficult to run down the plane tank to 200 psi. You should not run it below 100 per POH if I recall correctly. Therefore in our experience the lowest pressure we have been able to achieve in the supply tank before having to replace it has been around 400 psi. Nexair LLC is the company we used to supply the original metal hoses and connectors and through whom we lease the tanks. The 12 month lease is ~$130/yr per tank. The cost to refill a tank including delivery is about $90. Depending on your use you may find it advantageous to buy the initial set of tanks and then just pay the refill charge. Yes, you can use a two tank system as well. Nexair should help you decide what is best for you. Just make sure you specify aviator oxygen since as was pointed out in another comment it has no moisture in it and therefore won't freeze in the regulator at high altitudes. Hope this helps.
Hi Chris - I read that some years ago the compressed gas industry settled on one standard for all O2 (aviation, industrial, medical). Medical facilities add moisture between the source and the recipient. I’m not an expert in this industry, though, so take that as unconfirmed scuttlebutt.
