Had a conversation with some coworkers today about the different types of plasma cutters and we were wondering about how they're made. Most units you need to use a separate air compressor. Some have one built in. (Not looking to discusses the down sides to the built in ones, just the air itself.)

With a stand alone compressor you need like 90+ PSI and almost 5 CFM or better. But the machines with their own air aren't really any bigger in size. So what kind of tiny air pump is in there that does the job a big ass compressor is needed to do otherwise?

Not sure where you're getting your 5CFM number, but that must be a BIG plasma cutter rated for serious thickness!

In my limited knowledge/experience DRY air is much more important than BIG air.

That 90psi number seems high too. My little one runs on 40-45.

Not particularly big or expensive. (lowest models from companies anyone had actually heard of before looking on Amazon. lol )

 
HyperTherm is what the pros prefer, but they are pricey. Buy once, cry once if you really want a good machine.

I had a HyperTherm. It did not use much air, but as mentioned above it had to be dry. We always had at least 90 psi in the system, unit worked great. I was cutting stainless up to 3/8" thick.

Again, not buying, so not looking for recommendations. Just wondering how a small internal pump/compressor can do the job, but a large compressor is needed in another.

I assume it's BECAUSE there's mo tank to recover, and a constant pump of air does the trick. Just wondering what type and how it can generate enough PSI being so small.

You're asking the wrong question!

The question should be: "Do those plasma cutters having a small internal air compressor also have a real effective small internal air dryer?"

The answer is NO! At best they will have a small air filter/separator. An air filter/separator is not now (and never will be) a real 100% effective air dryer.

However over sized your compressed air supply; if the air reaching the plasma cutter nozzle contains water aerosol (tiny moisture droplets) your plasma cutter nozzle will shortly fail!

I own a 200 amp plasma cutter and designed refrigerated and pressure swing air dryers for Sullair Corp., Van Air Systems and Hankison for several decades before retirement.

I have not a clue what was just said above means to the OP. So let me talk about what I know. I use a hypertherm 45. I run nitrogen since that's more easily portable for me than a full compressor setup and that works great for what I do which is always cutting in remote locations running off a generator. I did get my nephew a hypertherm powermax30air for his wedding present. It has no issues running within its capabilities. Since hypertherm also makes a powermax30 without air you can see adding the compressor cuts the plasma capabilities of the system by some amount in both capabilities and duty cycle. I would guess its actually related to the amperage available rather than anything to do with the compressor air volume but there is no real way to know. Not having actually looked inside a powermax30 I have no idea what they do about air drying, but I can say they do automatically purge water since you can see that below the unit, but otherwise not sure the technology used since I have not opened it up. But in any case Hypertherm are seriously the best at this and what they have seems to work fine at that particular size. I have not seen larger units with built in air but I've not ever looked at anybody but hypertherm in this market given my experience. I can say because a local friend of mine cuts lots of steel with a bigger but still portable hypertherm that having stupidly dry air is not required as all he runs is a std commercial IR dryer and has not had an issues.

As I understand it (and admittedly, my experience is limited) dry air is about consumable life, not cutting ability.