Nitrox and Trimix blending- safe, easy and fast! | Stephan Fehringer | Dive Instructor
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Nitrox and Trimix blending- safe, easy and fast!

trimix diver with pscr rebreather and stages

Nitrox and Trimix blending- safe, easy and fast!

How to make nitrox and trimix blending fast, easy and safe for divers

Recently, our mixed gas filling station completed , tested and went into operation …
One time you´ll reach a point where you get tired of filling the tanks slowly and long winded with the filling hose using the partial pressure method!! We are technical divers and we want to go diving and not gasblending the whole day. So I decided to set up a different trimix / nitrox blending system. After a lot of research , I found out that such s.c. blending sticks are the fastest and safest way to blend nitrox or trimix and I dove deeper into this constant flow system. After learning the theory I started to construct myself the first prototype.

The construction of the constant flow nitrox and trimix blending system

constant flow nitrox and trimix blending system
A constant flow blending system to mix gases for diving is basically very simple.
You only need to add continuous helium and oxygen to the normal air into the entry side of the compressor. We use special commercial pressure reducers to get an intermediate pressure with downstream needle valves for precise dosage. To control the amount of added O2 and helium we use O2 sensors installed directly after every gas inlet. So you always know the blending ratio of your final breathing gas. Different to nitrox blending, on trimix blending you need to convert the O2 readings which is easily done with a simple excel calculation. The finished gas mixture become compressed inside the compressor and filled directly – after several filtration – thru a filling panel into our dive tanks. On our latest version of the electronics we´ve implemented another oxygen sensor which acts as a safety. If one of the (3) sensors put out an unsafe value (for the compressor and the whole system) than an upstream connected solenoid valve close the gas supply.
In our case we can connect up to four cylinders at the same time. So we have exact the same mixture of breathing gas in every tank thus results in the same decompression profile of every technical diver in the group which is the biggest benefit.
Another advantage is on topping up the tanks, specially if the helium or oxygen bank runs low. You don´t need to drain your cylinders anymore wasting your valuable trimix and you can use the bank till it´s completely empty.

Operating the constant flow system

nitrox stickIt´s always good to save money, specially for technical divers. The saved money from the fully emptied storage bank will amortize your investment on such a system but your saved time either. To be honest, I spend the saved money on gear now 😉

Okay, lets start gasblending: Just connect your cylinders, start the compressor and justify your wanted final mixture of breathing gas and just control the values, that´s it. During the tanks get filled you can maintenance your other equipment, stay in your shop or just drink a beer.


Important notice:

Always know your breathing gas! So analyse every tank before diving.
Never forget to respect your local laws and specially never do something unfamiliar without proper education and getting the necessary knowledge first!

If you have any further question or need help feel free to drop me a message. You can also do a nitrox- or trimix gasblender course with me.

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