Thanks Stuart, this thread got me thinking about using a small, portable compressor to power my booster. Based on other's experience (especially Tom's) I was able find one that performs well for me. (
DEWALT D55146 : 200 PSI 4.5 Gallon Electric Wheeled Portable Compressor) I used it to do a couple of Nitrox fills today and I am really pleased how things worked out.
The key was recognizing that you really want the pressure of the drive gas to be at the booster's optimum pressure all the time. Looking at what was available for portable, oil-less compressors I found that there has been an evolution in some models toward higher operating pressure. The DeWalt runs up to 200psi cut out pressure. More importantly the cut in pressure is 165psi. Since my Jetsam booster is designed to run at 147psi (10 bar), that means that the pressure at the regulator can be set so that this is supplied all the time, with no cycling below the optimum drive pressure.
The compressor's flow is rated at 5.3 cfm at 90 psi. It turns out that matched to the Jetsam booster this works out to a 50% duty cycle , well within the compressor manufacturer's recommendations. I added a small oil/water seperator for my own peace of mind, it is reassuring to look at the glass bowl and see no water in its trap. A small 1/4 inch ball valve was added to the seperator to control the drive gas.
Now I can fill my little rebreather cylinders to my hearts content, not having to worry if there is enough drive gas around to do the job. Thanks all!