how to tell a 2-stage; tank size?

Hi,

I'm actually just getting into marble carving, but this group seems like it knows the most about air compressors. I am investing in pneumatic hammers, which will consume from 3-6 cfm @90psi.
Some sort of small, handheld rotary tool could be useful as well for fine details where chisels would just break the brittle stone. Haven't shopped around yet; unsure what low rpm rotary tools are likely to eat up.

The air hammers are a continuous draw, and any future use will be air gravers, the aforementioned rotary tool, or spray guns for wood lacquers; all will be continuous. I only foresee one tool at a time; this is for my personal use.

I'm also on a budget (aren't we all), and am a college student, working under a large canopy in the back yard. Something moderately portable, and under 20amp 115V is a must.

I've read through some of the archives. If a 2-stage used compressor on craigslist pops up, I'm partially won over to its merits. Quieter matters; compact matters. Many of the sellers, however, don't say, don't know, can't tell... when they give the model number, and I do a google search, often even then the manufacturer in their little blurb mentions nothing of 2-stage or single stage. Is there a way, looking at the photo, to tell?

Actually, should I be won over? For continuous duty, is a 2-stage highly preferable, or simply indifferent?

What are those two-tank compressors for? Advantages?

Regarding tank size, I'm told on a stonecarving group that a pancake compressor will work for me. Work; nothing was said about work well, which is the question I want answered. I also looked up weight specs, and wow, a 20-gallon compressor weights just 20 lbs more than a 5-gallon I was looking at; at these smaller sizes it must mostly be in the motor. But 5gallon IS more portable. For continuous duty, is a smaller tank just fine, because then the motor will be running continuously, the tank hardly factoring in at all because the air is used up as soon as it is compressed? Or quite the opposite; the poor motor will be on and off every 30 seconds, and the extra gallons for a 20 or 30-gallon tank will be well worth it.



thanks!
-Bernard Arnest

If you want quiet stay away from anything oiless, they sound like a jackhammer running. If you want portable & 110v probably the IR Garagemate or something similar with a 26 or so gal tank would be a good bet. 220v compressors put out more air but most have 60+ gal tanks & are NOT portable. A 2 stage will have 2 cylinders usually one is larger than the other where a single stage like mine may have 2 cylinders but they will be the same size. Main advantage of 2 stage is they pump up to a higher pressure & thus store more air in any given size tank. Main thing to look for in a compressor is #CFM @ 90psi, HP numbers are about useless as they are wildly inflated & at least double what it actually does.

You won't find any 120V two stage compressors. An air hammer or aircraft rivet gun doesn't draw much air, but rotary units such as grinders and engravers will **** lots of air. I'll bet even my big 24 cfm unit would have a time keeping up with a air powered grinder of some sort.

Charles

SteveU said:

If you want portable & 110v probably the IR Garagemate or something similar.

Click to expand...

Yup.

Anything large enough to be 2-stage will have at LEAST a 60-gallon tank, and a 5HP motor that runs off of 220. 80-gallon units with 7Hp motors are more common.

110V, you can find some decent ones that are fairly quiet, and they'll run a grinder for a couple of minutes. But after that, you're going to have to wait for the tank to refill. An air hammer / air chisel will run on such a unit quite comfortably.

Also, remember to ignore the HP ratings. The only thing you're looking at is "CFM @ 90 PSI" on the tag. That's how you compare these things. They all fudge a little on CFM, but their HP ratings are ridiculous jokes.

Thanks!

That explains why I was searching in vain for some obvious way to tell

Hmm... I read on a buying guide that oil-less is much more expensive, and only used in the food industry, say, or other cases where any oil at all is a serious problem; why on earth are they making hobby-sized models, and so many of them? Unless people who haven't asked on good forums and who don't know better, get suckered into the idea of no maintenance because they're going to forget to oil it anyway....



anyway, I think I'm good to go now;
thanks!
-Bernard

I recently went through the same thing... looking for a compressor. I do not have 220vac access in my garage and I wanted something portable, but NOT oilless. I finally ended up with this:

http://www.sears.com/sr/javasr/prod...BV_EngineID=cdcdaddlgkggmelcefecemldffidfni.0

It was the most compressor that I could find that met my requirements.

BerninicaCO3 said:

Thanks!

That explains why I was searching in vain for some obvious way to tell

Hmm... I read on a buying guide that oil-less is much more expensive, and only used in the food industry, say, or other cases where any oil at all is a serious problem; why on earth are they making hobby-sized models, and so many of them? Unless people who haven't asked on good forums and who don't know better, get suckered into the idea of no maintenance because they're going to forget to oil it anyway....

Click to expand...

The oil-less compressors have a pump that is mounted directly to the motor. This is the case with the pancake models typically used by roofers and other contractors. There are many oil-less models in larger tank sizes as well, even some in a vertical configuration. Their motors run at 3450 RPM, making them quite noisy.

The compressor you are looking for will have a 1725 RPM motor driving the pump via a belt and pulleys, like the one eschoendorff posted. They are more robust and longer lasting than the oil-less units. Many are convertible to run on 110V or 220V. Find one with the largest tank you can afford.

Oil-less are either expensive or cheap. The food industry has to use some very pricy high end oil less. If that was what oil less was for the rest of us it would not have a bad name. For the rest of us think construction sites - nailers are where oil-less is best used.

Again you will find the major brands for compressors are not the ones you find at most common stores except one or two Craftsmen models most of the ones I see without going to farm supplies or specialty stores are junk. The most is underlined to prevent flames, etc.

Ya might want to look at quality electric power tools .............

Budget and lots of CFM from a air compressor dont happen.
I looked for a "deal" on a large used compressor for 2 years and all the deals are too far away to get and not worth shipping cost. ( and dont happen too often )

For the CFM of air to run grinders , drills and such you will need to go BIG on a 2 stage unit 240V at around or over $2000. and it dont stop there , you have to get air line set up and the tools.

Again , get some quality electric power tools.

Stay away from the cheap china junk.

On kind of a side note, years ago I worked at a place where we sandblasted marble and granite, with a rubber mask on the stone to protect the parts we didn't want to blast/paint. It is quick, comes out quite nice, is capable of very fine detail, and the depth of cut can be varied on the same workpiece.
You WOULD need quite a bit of compressor and 220V, though. Just an F.Y.I.