Air/Nitrox Fills

[Doc Harry]

... just how clean does the air have to be and stay safe?...

I will not offer any advice. But I will give you my real-world experience!

I use an Alkin W-31 oil-based compressor with a small integral air filter.

Air anlysis from the integral air filter meets all oxygen-compatable air (OCA) standards except dew point. Then, I run the air through a 24-inch LF filter and it comes out so clean and dry that it greatly exceeds all OCA standards.

I routinely fill three HC-4500 storage cylinders with EAN32 to 4,000 PSI by continuous blending.

I also do partial-pressure mixing and top off with continuous-blend EAN40 to make mixes in excess of 40%.

I completely disassemble everything down to machined parts (except the compressor) every year and perform a thorough oxygen cleaning.

I never leave the compressor unattended when it is running. I have a very large ABC fire extinuigsher at my escape route.

Can you be too safe? How much is your house worth? What would your house look like with a big fire fueled by high-pressure oxygen? We've all got to determine how much risk we are going to take.

Clearly, my risk is running EAN40 though an oil-based compressor at 4,000 PSI. But I've never had any problems in 3 years of operation.

 

[rjack321]

OK, I hope I dont get beat up for this but Im getting set up to fill my own cylinders.. I have the big MC1A compressor and yes I will be sending off for an air test. I have no doubt I can easily produce breathing quality air but I would also like to produce O2 compatible air and blend my own nitrox. This is where it gets shady for me. Everything seems to be greatly exaggerated for extreme safety but I would like some real world answers.. just how clean does the air have to be and stay safe? Going by the tables you can breathe air with 20ppm oil particles 15,10ppm hydrocarbons water and so on.. but for O2 it drops to an amazingly clean 0.5ppm! Is the main danger the risk of explosion while filling or is it also harmful to breathe EANx mixed with "normal" breathing quality air?? I mean other than the nearly 100% O2 present in the cylinder during filling after mixed the typical solution is only 11% more O2 than plain air.

Its not hard at all to make air with <0.5ppm hydrocarbons. While this sounds "amazingly low" etc. its really not that difficult to achieve in practice. Many primary filters achieve this (but not near the end of their life). Running a 2nd filter will get you there and provide a backup when you've exceeded the capacity in your primary.

 

[paxtang]

i use an alkin w-31 oil-based compressor with a small integral air filter.

you mean the intake filter on the compressor??

i routinely fill three hc-4500 storage cylinders with ean32 to 4,000 psi by continuous blending.

please explain continuos blending

.

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[Blue Abyss]

Doc is referring to the filtration after the compressor. The w-31 has a smaller filtration unit mounted on the compressor rather than a larger more complicated separate filtration system. Not uncommon on most smaller compressors. Many people, including Doc, have addtional filters mounted seperatly from the compressor to assure that the gas is oxygen compatable.

Secondly continuous blending means you inject a measured amount of oxygen into the intake of the compressor to create nitrox before it enters the compressor. Then the compressor will compress the gas which is then filtered and delivered to the banks or tanks.

As many have said before get the Oxygen Hackers Guide. They give a much more complete description of continuous blending and many other helpful bits of information about running a fill station.

Good luck

 

[paxtang]

I have the book ordered, cant wait for it to get here.. All the fuss about everything being "oxygen clean" and then you can just blow pure oxygen into the intake of the compressor?? Seems like it just completely contradicts everything.. Couple more questions if you dont mind..This compressor was gone over and put back into service by a company I dont rem now (there is a tag on it with their name) and its obvious there were some lines here and there replaced,, fittings and so on.. also it was obvious there were new oil and fuel filters on the engine.. clean oil in it and the compressor as well.. how do I know if its the fancy compressor oil in the compressor or just plain compressor oil? and do I need the fancy food grade stuff? can you use vegetable oil? I know, I ask alot of questions.. I appreciate all the help, thanks.

 

[Blue Abyss]

The only way you would know what oil is in the compressor is to ask the company who serviced it what they used. You cannot tell by looking.

Most people who do continuous blending use synthetic oils. You will need to check with the compressor manufacturer as to what synthetics to use.
Note that nearly all compressor manufactures will tell you that you cannot do continuous blending with their compressors.

Also you may want to ask how to do the oil change. Depending on the compressor and the age you may have to do a few oil changes in a row as a result of switching to synthetic.

 

[paxtang]

Well good news and bad news.. I got the results from my air test but they goofed.. I sent in for grade E and they only tested for grade D which as far as I can tell passed with flying colors.. here is the results
Oxygen 20.8
C Dioxide 417
c monoxide <1
water vapor 19.67
dew point -67
Oil/part <1

these are all way below the standard limits and all but the oxygen is the same for grade E air which mine is in the limits for that as well.. the only thing they didnt test for was the hydrocarbons.. I am getting a re-test of course but my question as of right now is this.. Can I breathe this air right now as is or should i wait for the re-test??

 

[oxyhacker]

It's all about the pressure of the O2. When you prime a tank for partial pressure mixing, the tank and valve are exposed to 100% oxygen. When you run the O2 into the compressor intake it is thoroughly mixed with the air (if the continuous mixer is doing its job) so the compressor never sees more than 40% (or whatever your personal limit is) of O2. The assumption is that 100% 02 at 1500 or so psi is potentially more dangerous than 40% at 3000 psi. Of course in real life oil and temperature enter into things, but there don't seem to be a lot of compressors exploding (which isn't the same as saying there aren't any), so the logic seems to be fairly valid.

BTW have you seen the Alkin threads here and elsewhere? There is a general feeling that the little Alkin is not really the continuous-duty 4500 psi machine it was originally promoted as being. I would not try to skimp on oil, and would keep a careful eye on temperature. It probably wouldn't be a bad idea to fill only one tank at a time, and let it rest a couple hours in between.

All the fuss about everything being "oxygen clean" and then you can just blow pure oxygen into the intake of the compressor?? Seems like it just completely contradicts everything.. Couple more questions if you dont mind..This compressor was gone over and put back into service by a company I dont rem now (there is a tag on it with their name) and its obvious there were some lines here and there replaced,, fittings and so on.. also it was obvious there were new oil and fuel filters on the engine.. clean oil in it and the compressor as well.. how do I know if its the fancy compressor oil in the compressor or just plain compressor oil? and do I need the fancy food grade stuff? can you use vegetable oil? I know, I ask alot of questions.. I appreciate all the help, thanks.

 

[paxtang]

Alkin? I have the davey compressor. And after a couple phone calls and some checking on their part turns out they did do the grade E test (not sure if they always test that way or not) but only gave me the grade D because they thought thats what I payed for.. geesh.. anyhoo.. im certified grade E!! whoo hoo..

 

[miesemer]

What would your house look like with a big fire fueled by high-pressure oxygen?

Like this