USUN XB30 Drive with "Shop" air?

[InWay2Deep]

I've got a USUN XB30 for booting 2L and AL40's. I can't seem to find the CFM requirements for drive gas. Just the 8.3Bar max input pressure. This is easily done using a regular "shop" air compressor. Anyone have a setup like this? What compressor do you use and what kind of pre-filter do you have in place? Would a little pancake compressor keep up? Trying to minimize trips to the dive shop for drive gas if possible as I have an H bottle of O2 I'm filling from.

Thanks

 

[Dave1w]

I did try using mine with a small compressor, and a separator, but at the low flow rate, the separator didn't work very well, and when I stripped it, it with filthy. I was concerned at the minimal separation between the drive and O2 side

 

[greeniguana]

I have a "small" 2 stage 20gal compressor which does 5.5cfm at 90psi. It does rebreather bottles fine, but I have to wait for it to refill on anything larger when pressure gets above 2500. Due to the large volumes of air required it would be a good idea to have a large cooling/filter system.

 

[broncobowsher]

A little pancake compressor won't do it. I go with a generic calculation that it takes a scuba cylinder of drive air to fill a rebreather bottle. There can be a lot of variation to that, what is the start pressures of both bottles, how large of a scuba cylinder, etc. With that you have an approximate cubic feet of drive gas needed.

But there is more. Most home shop style compressors are not rated at 100% duty cycle. They will burn out if run full time. It actually takes a fairly large and robust compressor to do it right. I run a 5HP Ingersol Rand 2-stage on a 60 gallon tank. It will keep up and cycle at about a 50% duty cycle running my Haskel.

Large tanks are nice for a couple of reasons. Probably the best overlooked one is the large surface area. That works good for cooling the air.

2-stage has a benefit that is way overlooked at drying the air. Being compressed to a higher pressure forces more of the water to condense out. Then when you regulate that air pressure down to a lower pressure it is dryer. Much like how air from a scuba tank is nearly as dry as possible, the water was squeezed out from high pressure so you don't get any at low pressures. Same thing happens to a lesser degree running a compressor at a higher pressure than your operating pressure.

Another factor of running higher pressure is the compressor has a hysteresis on the pressure switch. The compressor may cycle on at 150 PSI and off at 175 PSI for example. It will be listed as a 175 PSI compressor. But will deliver only 150 PSI (or less) of consistent air delivery.