the scuba zone - Alkin W31 Compressor
Alkin W31 Compressor

On the booster page, I mentioned my desire to blend my own gas for the Rebreather. However, the lure of "fully self contained gas blending" continues to grow.

Since summer of 2007, I have been using my Jetsam baby booster to fill my O2, diluent and suit gas cylinders. I also used the booster to "clean out" my first K tank of O2 by boosting it into an O2 cleaned 80cf aluminum cylinder. My current gas blending system consists of two K bottles of O2, one T bottle of He, one AL80 with O2 in it (convenience) and one AL80 filled with "shop air". I take this tank to the dive shop to be filled with straight air (21%), which I then use as my "top off" supply. With the booster, I have been able to fill the O2 cylinder and top off the diluent and suit gas bottles with no problems. Since adding Helium, I am also able to blend trimix for diluent and bailout as required.

The problem is that one is never satisfied. This system works very well, the tank of air is a finite resource. After just a few top-ups, the pressure is down below 1500 psi and it gets harder and harder to fill the suit gas and diluent to 3000 psi. This becomes even more difficult as I start mixing Trimix diluent, as the top up is at the high end of the desired pressure. Making up a trimix bailout, even just my 40cf bottle, also uses a large chunk of the air reserve. To make up a trimix bailout in my 80cf bottle would require a trip to the dive shop for a top-up. As always, it's not about the cost ($4.00 for an 80cf air fill), it's really about the convenience. At 32km each way, dive shop trips do also add time and gas costs to the equation.

I've always followed the "home" compressor threads on the internet forums with interest, but found the initial cost of a 300 bar compressor to be too large to consider. That is, until I started hearing about the Alkin line of compressors. After reading about the Alkin for some many months now, I decided to investigate further. The Alkin is a low-volume compressor that has garnered favorable reviews from all over. Further investigation showed that they are reliable and quite a bit cheaper than many other compressors yet very well built. After looking through the various on-line catalogs of Alkin compressors, I chose the W31 (300 bar, 3.5 cfm) driven by a 220V electric motor. It was inexpensive (compared to other brands), quiet and small enough for home use.

Now to find one in Canada, or that would ship to Canada without costing an arm and a leg. Lucky for me there is a fairly close dealer for Alkin: Canadian Purcell Machinery in Cranbrook, B.C. After a visit to their website and some emails, I had a price quote that was very reasonable for a machine delivered to my neighborhood courier depot. I sent in the cheque, and less than a week later I had my brand new shiny Alkin W31 compressor.

I was impressed with the shipping. The unit arrived in a nice wooden crate with all components included. The unit is very well built, and the Canadian version features a proper CSI approved 220V motor and standard 20A plug. I went to Home Depot and picked up the parts to build a 40A extension cord that connects to my glassblowing annealer's plug-in, and after some construction was set to go.

The manual is complete and easy to follow. Start up, run-in, operational and shut-down procedures are well laid out.

The basic unit comes with manual water trap drains and no pressure cut-off switch. There is an option to add automated drains and a pressure cutoff switch, but this adds $1800 to the price. Since price was a consideration in my purchase decision, I opted to save the money and go manual. Besides, most of the tanks in rebreather diving are small, so there is little requirement to build an air bank, which is where the automated parts really pay off.

One thing to point out to any prospective owner. The unit appears to come only with a yoke fill whip, but once I got my unit I could see the yoke fitting was actually a standard DIN-to-Yoke adapter on a DIN fill fitting. My DIN fitting was stiff, but after removing the Din-to-Yoke adapter it came free and now works very well. So any technical divers - don't fret - the Alkin W31 comes complete with BOTH a DIN fill whip and a DIN-to-Yoke fill adapter.

Below are some pictures of the new Alkin W31 compressor, just out of the box and not yet started. Also shown is the fill whip sitting in a sink (don't ask).

Alkin W31 Compressor Alkin W31 Compressor Alkin W31 Fill Whip T320_fill station 031108 1.jpg
Update - March 12, 2008

The unit comes with a standard L6 250V 20A industrial locking plug. I bought components and built an industrial (welder) 240V to L6 extension cord, but soon discovered that it was overkill. As per the manual, I ran the unit with all drains open (0 pressure buildup) for 10 minutes to season the compressor. During this time, it became apparent that the compressor is quiet enough that it can remain indoors during operation. To accomodate this, the stove outlet on the main level was changed to a dryer outlet, and I added an L6 plug to a spare dryer cord so that I could use the compressor in my "gear area".

I think I'll change the dryer outlet to a proper L6 outlet as I don't need the extra extension cord.

This week I've emptied and filled my suit gas bottle (6cf) a few times, as well as an 80cf bailout bottle and topped up my Prism 19cf diluent bottle. The compressor is very nice to use, and fills an 80cf bottle from totally empty (changed valve) to 220bar in 30 minutes.

Here is a picture of my Alkin W31 fill station. The bag of flour just happens to be in the picture.

Alkin W31 Fill Station

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