Many years ago, I came across an old Bauer 4 stage portable air compressor in a junk yard. I bought it for scrap weight and never did anything with it until I bought my FX Crown. This compressor was just the pump without controls. So I designed and built a high pressure control system with all the safety interlocks, gauges and output manifold. It really isn't so portable, as it weighs 250 lbs and runs on 400 volt 3 phase power, but I have that available. I scrounged two 12 liter aluminum scuba tanks and re-valved them. The compressor will fill a tank to 230 bar from empty in 40 minutes. The compressor is rated at 80 liters an hour and 250 bar max pressure. I can fill the Crown many, many times before tank pressure drops below 200 bar.