partial pressure blending

[fredk]

Looking for any suggestions on the least expensive way to go about partial pressure blending? Up here they want crazy $ for hyper pure filters and after investigating the nitrox stik our compressor manufactuer will void the warranty if you pump o2 thru it, it's a brand new compressor so don't want to fool with that one. Anyone out there with a contact for an inexpensive setup send me a pm.

 

[padiscubapro]

Originally posted by fredk
Looking for any suggestions on the least expensive way to go about partial pressure blending? Up here they want crazy $ for hyper pure filters and after investigating the nitrox stik our compressor manufactuer will void the warranty if you pump o2 thru it, it's a brand new compressor so don't want to fool with that one. Anyone out there with a contact for an inexpensive setup send me a pm.

If you are going to do PP blending your gas must be hydrocarbon free.. The big problem is not at the beginning, but as you pump gas your hoses and fillers will accumulate hydrocarbon residue, you will also be depositing the same in your customers tank, as time progresses the risk increases.. There are many people pumping an incresed % of o2 into their compressors, a preblending is better than a membrane which pumps the output back into the input so the effect is increased.. If the gas is "blended" with air befor the input to the compressor you are not pumping O2 so you probably aren't voiding your warranty unless is states a % of 21%.. If you do plan on pumping a higher % of o2 than air you must increase the cooling of your compressor, most compressor fires are due to heat.. The final stage of most compressors is extremely hot..

If you can cool your output dramatically you can increase the effectiveness of your filters so you can get more out of them.. The water seperators and filters don't work as well as they could if the gas out of the compressor is cool..

I have a RIKS compressor that all 4 stages are water cooled.. I can put my hand on the 4th stage without burning myself.. I pull out water vapor at every stage, My filtration still functions well when most other would be failing with the media in the same condition.

 

[maddiver]

check under 'garage mix' at http://www.deeperstuff.com/

it will have all your answers as well as pick up a copy of oxygen hackers handbook through airspeedpress.com

Originally posted by fredk
Looking for any suggestions on the least expensive way to go about partial pressure blending? Up here they want crazy $ for hyper pure filters and after investigating the nitrox stik our compressor manufactuer will void the warranty if you pump o2 thru it, it's a brand new compressor so don't want to fool with that one. Anyone out there with a contact for an inexpensive setup send me a pm.

 

[omar]

This is a fair series of articles on setting up a mixing station. However, this is not in his garage, what you see is only part of the system and there are a number of inconsistent statements and flaws in his logic. One of the most glaring problems with this setup is the lack of check vales on the oxygen lines and no electrical grounding for the oxygen stuff as well. This is in an airport hanger in Florida where a lightning storm is very likely.

If I was designing a true “price is no object” system it sure as heck would not use scuba tank valves for controlling flows. It would also have a heck of a lot less high pressure lines running all over the place. Also, I got a good laugh over the statement that a helium analyzer was not cost effective when the cost of all the unneeded pressure lines in this setup is more than an analyzer.

One major point is if you are not analyzing your mix you DO NOT know what is in it. Whether it is oxygen or helium. The guys that top off their cylinders with out a means to check the contents are asking for a screw up at some point.

omar

 

[maddiver]

I understood the question to be how to set up the cheapest part press blending station and this site already had the cga fitting numbers plus where to get them outlined. Possibly a help to someone who is just starting out. I don't think this guy has thirty grand to put toward DIR fill station for a million cft (obvious exaggeration) of gas per month etc.... Also when you read things that others have done or are doing it helps you not repeat their mistakes....not all of us like reinventing the wheel....merely attempting to provide a source of information.
Thanks for your assessment on his top level system its always good to have a professional viewpoint.

Originally posted by omar
This is a fair series of articles on setting up a mixing station. However, this is not in his garage, what you see is only part of the system and there are a number of inconsistent statements and flaws in his logic.

If I was designing a true “price is no object” system
omar

 

[VTWarrenG]

I was under the impression that continuous blending is much cheaper than PP-blending, but much slower.

Here's what I'd like to do in my own garage: Use a couple of adjustable-flow orifices into a manifold, through a Haskel, and straight into a scuba tank. That setup would require no banking, only one high-pressure line, would not create skimming or remixing problems, etc. It's also so small it'd fit in a closet. Are there errors in my logic?

- Warren

 

[maddiver]

Warren-

I think for a commercial set up divers and employees will not be willing to take the extra time. In a commercial (i mean retail by this) setting as opposed to your garage, time is money several times over and your probably going to get several requests at a time not spread out over time.

Originally posted by VTWarrenG
I was under the impression that ....but much slower.


- Warren

 

[VTWarrenG]

maddiver,

Well sure.. I guess I'm just checking my logic on this... the most tanks I'm likely to ever fill at once is probably four sets of double 104's, and even that would be very infrequent. I don't mind waiting a while for a tank fill, because even the slowest of compressors will only require half the time (not to mention inconvenience) of driving to the shop, unloading tanks, waiting, waiting, waiting some more, loading them back up, then taking them back home.

I don't plan on banking at all, but a very simple continuous blend system can easily accomodate banks later on. It just seems so damn simple and easy -- three cylinders of UHP Helium, aviator O2, and air (which I'll compress myself), a compressor/booster, fill whip, and analyzer.

What are the downsides?

1) The compressor/booster is very expensive, both to purchase and to maintain. How expensive? Haskel's HG series gas boosters seems pretty ideal for this application. They look pretty small, too.

2) It's slow. How slow? 10 minutes per fill?

*shrug* I don't know...

- Warren

 

[omar]

Warren,

You would need a blender for the gas prior to running it into the compressor. This is to ensure a fully mixed blend so you don't end up with a high oxygen content stream. There are some inexpensive but good inline mixers that will work for this application. And you don't really need a Haskel. For the majority of divers the best mix for the depth would not be such that running a trimix through the compressor will screw it up.

I have been doing continuous blending of trimix for over 2 years with a common scuba compressor with no problems.

omar