compressor requirements for partial pressure blending

[daddybear]

If you were to use a partil pressure system to fill tanks to 100% o2 could you then fill ordinary tanks with the same compressor afterwords. ie what would it take to fill normal tanks with air then to top off other tanks with 100% o2 in it. does the compressor have anything special done to it to top off these high o2 tanks? appreciate being enlightened, thanks,cameron.

 

[phantomrfa]

I think i know what your asking.(I dont pp blend nitrox so this is what i have learned from this site and my be wrong)The compressor is the same for air/nitrox, the diffrents is the filtration.you need grade E ,for AIR diving which has very little hydrocarbons ,but even better air for O2 mixing with nearly "0" hydrocarbons. This is done by more/better filters(remember the fire triangle O2+fuel+heat=you dead)The second part can you fill off a pp nitrox compressor ,YES the air is just cleaner

 

[halocline]

I'm pretty sure that anything that comes in contact with high concentrations of O2 must be 02 clean. So, that would certainly mean that the air produced by the compressor used in partial pressure blending would have to meet 02 clean standards, as would the tank and any equipment in the air path, like fill whip, etc. Not just when filling partial pressure tanks, but all the time, because if non-02 clean air was flowing through the whip, I would think the whip would no longer be 02 clean.

Now, an interesting question to me (maybe obvious to someone who knows more) is, lets say your compressor and air path is 02 clean, and you use it to fill a non-02 clean tank with 02 clean air. Is there any sort of cross contamination to the fill whip? It's a pretty paranoid scenario.

 

[pescador775]

Under some circumstances there could occur a back flow from the SCUBA tank. To me, that would be irrelevant. If someone felt differently, they could install a check valve in the circuit. Normal practice should include procedures and this is fairly obvious, don't open the tank valve until a high head pressure is verified at the whip. Most compressors with commercial filtration systems seem to produce better than Grade E air. The subject has been discussed on SB and I have offered data and a hypothesis to support this. However, it would be understandable if the compressor operator added an extra canister to extend the life of the system and also effect an incremental improvement to air purity.

A big problem with compressed air is water which may damage steel tanks and cause some aggravation to ice divers. When compressor manufacturers moved to comply with more stringent moisture levels under the latest version of Grade E they also concommitantly reduced oil vapor levels, even though the criteria for Grade E vapor and hydrocarbons had not. So, by reducing moisture they may also have reduced other contaminants which concern PP gas mixers. I believe that this is the case and that the oxygen clean issue has been overblown. Certainly, the expensive solutions offered do not apply to everybody with a small compressor. A potential contaminant not discussed in any document outside the govt is carbon. Even this is controversial and the 40 micron filter pads probably take care of it. However, I feel more comfortable with a stainless steel, 5 micron element installed in line. This mainly applies to self packing as commercial cartridges usually include an element in the cartridge itself, made from compressed silica dioxide I think.

 

[hawksbill]

If you are considering PP blending you need to read this book. Oxygen blending and more. You will see it refered to over and over as it addresses so much and so well written.

Vance Harlow's OXYGEN HACKER'S COMPANION From AIrspeed Press