Truth about Nitrox and how to get your fills - Garage Mix

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Posted by Maddiver on November 14, 2001 at 09:05:03:

You can start at home for ~$150 set up and your fills are about 84 cents thats right 84 cents! per 80 cu ft cylinder of course you need to then pay for your requsite fill but if you can't afford the 84 cents I'll send you the check.

Garage Mix - Part I
What’s your options when shops can’t help

The biggest obstacle confronting the adoption of EAN and helium in SCUBA is its lack of availability and high cost. Long time "air" advocates and their disparaging remarks are not the source of delay.

The purpose of this article will be to describe what I did to solve a problem. It was NOT designed to be a "cookbook" or instruction manual, nor was it written with the intent of instructing others on how to design or assemble a like system. The high pressures and dangerous gases one will encounter when working with the described components require training beyond the scope of this article.

Important TERMS
The bottom of this article contains a dictionary for reference. Use it when encountering a term you don’t understand.


After earning my "mix" certification many years ago, I was an eager and anxious tek/wrecker ready to get started with all the shipwrecks I had only heard about previously. Charters were scarce, but armed with persistence and a great deal of enthusiasm, I could usually locate a fun-filled day of wreck diving adventure somewhere within the State of Florida to keep me busy. As charters gradually came and went however, and my logbook started filling up, another problem materialized that caught me unprepared. I began to realize that obtaining gas fills would be one of the more difficult obstacles I would encounter!

For a list of the problems I encountered trying to obtain fills from shops


The shop does not blend He
The shop was out of gas
The shop was out of gas because the delivery driver hadn’t shown up yet
The shop was out of gas and they don’t know when the next delivery is
The shop had gas, but the pressures in all banks were too low
The shop had gas, but the "gas blender" had no time to fill them
The shop "gas blender" is on vacation and won’t be back for two weeks
The shop had gas, but won’t fill beyond the 2400 PSI rating
The shop filled the cylinders, but analysis indicates the percentages inaccurate
The shop fill system had a tendency to put water in my cylinders
The shop compressor was down
The shop can provide "mix" fills, but needs 2-3 weeks advance notice
The shop does not promote EAN or He based diving

Do you think these scenario’s are an exaggeration? Think again!! As an experienced "mix" diver, I can tell you these are exactly the battles I faced in trying to obtain mix and deco gases. The most annoying problem was getting fills several days before a charter (you have to work around the shop hours), the weather changes, and now the dive is cancelled leaving me with fills I might not use. After all the expense and trouble of obtaining gas, the last insult was the possibility of dumping perfectly good mix.

There were a few good shops who helped along the way and to them I will be forever grateful. I’ve made it a point to patronize and give them my business whenever possible. The downside is that knowledgeable shops who cater to the technical crowd are far and few between.

Getting Started

Before attempting to mix gases of any kind, locate a gas blending course of instruction from your local technical dive operation who specializes in such procedures. In addition to learning proper technique and protocol, the shop might then be used as a source of information, as well as assisting with the later purchase of gas blending hardware.

I realized right from the beginning, that before anything was to get constructed, that I had to ask myself some tough questions if I wanted to get into the business of doing my own fills. I felt this would facilitate direction I would take, and would assist in defining exactly what my needs were. This way, I might prevent problems down the road and eliminate unwanted expense due to poor design.

The questions I asked myself were 1) How much was I willing to spend?

2) Would I be blending just O2, or O2 and He?

3) Do I have adequate floor space and would gas deliveries be possible where the fill station was located?

4) How many people will I be blending for?

5) Can the local shop provide air top-offs, or must I purchase a HP compressor?

6) Is electrical service available in the event I purchase a compressor

My answers to the questions were as follows

1) Cost was less of a concern for me than most others.. As an active diver, I was already being presented with some rather large gas bills from the various shops, and there was no end in sight. Down the road, I felt any system constructed would pay for itself over many years and also might be resold some time in the future to recoup expenses.

2) I had no intention of just blending O2, but it was critical that I include He in my design.

3) Floor space was not an issue and the system would be placed in an area where gas deliveries would be possible.

4) The design would be kept simple with fills for one or two people at a time being normal.

5) I would purchase whatever compressors necessary so air top-offs from a shop would not be necessary. In addition, the location of the fill station was such that the noise generated from the compressors would not be an issue.

6) The existing electrical service had room for expansion. I ended up needing an 80amp circuit. Beware, as this is a rather large electrical requirement!

Obtaining Gas

I didn’t put anything together until ensuring I could get O2/He from a supplier.

I will not spend much effort describing how hard it was for me to initially obtain gas. Let’s just say I found mentioning two things getting me expelled from most gas suppliers. Any mention of "SCUBA" or "breathing gas" usually resulted in an immediate escort to the front door. I left disappointed and angry. However, simple observation left me convinced that I knew as much, if not more, than most in this area due to the large amount of time and effort I had put into researching this subject. I was determined to find a solution even if I had to go it alone. Looking back, I now know I made the right decision by not giving up.

To shorten the proverbial story, gas was eventually obtained by purchasing deliveries through an established company. No mention was ever made of SCUBA or "breathing gas".

The gases I had delivered were Aviator O2 and UHP Helium. Forget medical grade O2, or anything less than Aviator grade. Realize that all O2 comes from the same manufacturing process. It’s the subsequent handling and labeling that largely distinguishes the grades. Aviator O2 I discovered was best, because it was already designed for human consumption and was much easier to obtain then medical grade. UHP helium (Ultra High Purity) was an already established gas in use by others so I felt comfortable going with this grade.

Gases I ended up using were UHP Helium and Aviator O2.

System Number One
Inexpensive and simple for O2 and He

My quest to obtain a personal fill station did not occur overnight. In fact, the current system I own today is the culmination of several years work. It began with the purchase of a simple transfill whip and several other pieces of hardware which got me started performing relatively uncomplicated "mixing" procedures. As time progressed, it became obvious that a much more sophisticated and professional system was necessary, and this led to my interest and desire to take what I currently owned (at that time) to the next level. I might also mention that "mixing" requires some software tools to assist with the partial pressure blending process. At this time I purchased MixMaster, a rather easy and inexpensive utility from the folks at Diverse Technologies ( There are others, but this is what I used.

Early on, it was necessary to obtain a source for gas mixing hardware. Quite by accident I discovered where many shops purchased their own parts and pieces. It was Global Manufacturing Corporation. This company specializes in the many types of gas products necessary to run a SCUBA filling station; everything from gas flow control hardware, gauges, instrumentation and metering devices, to lubricants and test bench accessories for regulator repair. I obtained their catalog by simply calling and asking. As I mentioned earlier, I discovered them by accident when researching this subject many years ago, but I might add that since that time, I have discovered other sources of this hardware. This was necessary since GLOBAL generally discouraged me from obtaining their products, so I simply found other sources. For the purposes of this article however, I will use their catalog for reference.

On the day I called GLOBAL they were quite cooperative; however, they tend to support dive shops only and frown on any one person who calls in a order to obtain supplies for personal use. This is a typical response of the SCUBA industry. The reasoning seems to be that only a dive shop has a "trained professional" capable of employing or utilizing their resources, or perhaps they are just trying to protect their distributors. In general, DIVE SHOPS DO NOT PROMOTE THESE PRODUCTS because the general attitude is that the diver off the street is not capable of using them in a professional manner! Of course I disagree with this, but this is just my opinion. I think the biggest casualty of this righteous attitude has been dive industry itself. It can now claim responsibility for simultaneously holding back any progressive movement towards mixed gas diving as well as demonstrating their disregard and general misunderstanding of the proper breathing gases to employ for recreational OR technical diving. I offer as evidence PADI's taking until January 1996 to formally recognize EAN, and their concerted effort to destroy any proponent of this technology prior to that time. How long will it take before they embrace He based breathing mixes??

In any case, I felt it was extremely important that I obtain a catalog if nothing but to study it and learn more about gas mixing hardware. I have shown GMC contact information below:

Global Manufacturing Corporation
1829 South 68 Street
West Allis, WI 53214 USA

In the event you do not have the GMC catalog yourself, I have included scan's here as a reference. This will assist when I discuss the many different components of a fill station. In addition, I will use this catalog as it demonstrates the many choices I was confronted with, and also shows Globals' recommended solutions. The photos also graphically demonstrate the types of equipment necessary even though I did not purchase all of these parts from Global. Be aware all references came from the 1999 catalog. If you obtain a newer addition, the pictures might have changed somewhat, but as a general rule, their part numbers do not. However, you should double check all numbers from their latest catalog!

Anybody can bolt together a lot of hoses and pipes and call it a mix station. My goal was to build a system that employed fault tolerance and safety in an efficient design that would PREVENT an operator from making mistakes or injuring them self while simultaneously blending gas easily.

My first system consisted of the following items:

1. CGA540 (oxygen fitting)
2. part # 45020
3. part # 45341 (comes O2 compatible)

Item one was purchased from a local gas supplier. Items 2 and 3 (see photo's right) were purchased from GMC.

I attached the CGA540 to item 2 (above). Item 3, the flex whip, was then used to fill a standard SCUBA cylinder, regardless of size or valve (yoke or DIN). A DIN fitting on your SCUBA cylinder might require part # 45185. The CGA540 mates to a standard O2 supply cylinder, and part # 45020 then allows the flex whip to attach to the O2 source with the other end connecting to your SCUBA tank.

This same system can be used for He, except that item 1 must be a CGA580 (inert gas). Take note of how item 3 was constructed by GMC. It uses a stainless steel braided hose (oxygen cleaned) and uses a NO OIL gauge. Of course other designs and components are possible! This is just what I started with.

This basic system is relatively inexpensive and obviously quite simple, plus it can be used for both O2 and He. It's downside, like most of the cheaper systems, is that it does not entirely solve the "skimming problem". The skimming problem will be discussed in detail later in this multiple part article, but the short story is that once a supply bottle of O2 or He is drained and no longer contains high pressures, it becomes just about worthless for "mixing". Nonetheless, it works great for EAN recreational mixtures assuming you can obtain "air top-offs" from your local shop. For example, suppose you require EAN32 for a recreational dive, then you really don't need very much pressure in a O2 supply bottle. However, assume you are looking to fill a deco bottle, such as an aluminum 40cf, with 100% O2. In this case, you really need at least 1500-2000 PSI in your O2 source. The solution here is to keep plenty of fresh source bottles around for filling, and your problems are just about solved! AS LONG AS YOU HAVE ON HAND SOURCE BOTTLES CONTAINING HIGH PRESSURES, THIS SYSTEM ACTUALLY WORKS QUITE WELL!!! There is a slight expense associated with keeping on hand plenty of source bottles since lease fee's generally run in the $5-8/month range.

There are many variations of system number one. A simple one might be the substitution of part # 45020 with part # 4500. This basically incorporates a hand wheel with the CGA540 oxygen fitting which eases the burden of using a wrench to fasten/unfasten the CGA fitting to your source bottle. I have seen systems employing quick disconnects as another example. There is not enough room here to discuss them all. The basic system has been described, and I will leave it to the readers imagination to come up with more. Photo (right) demonstrates another simple variation as proposed by GMC. Its a nice little package, but I suspect it carries a hefty price tag, especially due to the digital pressure gauge.

LP - low pressure, generally meaning pressures under 3000PSI
HP - high pressure, generally meaning pressures 3000PSI and above
O2 - oxygen
He - helium
EAN - Enriched Air Nitrox
source - or source bottle, a cylinder containing gas used as a source supply, e.g, a bottle of gas delivered from a gas supplier

Shamelessly stolen from

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