I need an air compressor for a Plasma Cutter but not sure which one

admin

I have a Hypertherm Powermax 30 and need a compressor for it.  I don't want a big unit or expensive one since I will only use it very occasionally and I don't want anything to take up a lot of room or cost a lot.  The HP 30 needs a minimum of 3.5 CFM but they recommended 4 CFM @ 90 psi.  I've been looking on CL and see a few that look to be in good shape.  I'm not sure if I should look at a used one and also some that I've seen show the air delivery is in  SCFM instead of CFM.  Not sure if they are the same air flow.  Also would an eight gallon tank be enough for light usage or will it be too little.  Again I'm not a fabricator I just want something to play with in my garage.I would appreciate any input you could give to me.ThanksLast edited by medicineman; 03-14-2012 at 09:55 PM.
Reply:to little !!! im using a CH that puts out 200 psi on a 15 gal. tank at3.7 cfm @90 psi  and i with the air force 400 i think it needs more cfm to keep it from making the compressor cycle so muchLincoln Power Arc 4000 Thermal Arc Fabricator 252 iThermal arc 186Thermal Arc 26 tigTweeko 200 amp spool gunHobart AirForce 400WP-17V-12R
Reply:I had this one for my home.  Works great when I had the Miller 375 Xtreme which calls for 5 SCFM as I recall.  This compressor never was "not enough," but I wouldn't go smaller.  You can find it at Home Depot.  And yes, SCFM or CFM is the same thing.   I searched and searched and searched for a home compressor when I had the 375 plasma cutter.  (I've since moved up to a larger plasma and bought a very big Ingersol-Rand compressor from an estate sale).  I sold the 375 and the Dewalt compressor as depicted below.  You WON'T be sorry with that purchase. http://www.dewalt.com/tools/compress...ic-d55168.aspxLincoln Power Mig 216Lincoln AC/DC-225/125Miller  625 X-Treme PlasmaMiller 211 Forney 95FI-A 301HF 91110Victor Journeyman O/PMilwaukee DaytonMakita  Baileigh NRA Life Member
Reply:That is real nice but I was hoping I could find something a little smaller that would work well for my limited usage and budget.  What do you think the smallest size tank that would be acceptable and give me 4 CFM @ 80 lbs.  What do you think about this smaller dewalt it is only 4.5 gallons but the CFM is the same at 5.  http://www.dewalt.com/tools/compress...ic-d55146.aspxOr something from HF in the 8 gallon size for about $199 - $179 range or would that just be junk that I would be disapointed with even with limited use?Would you recommend buying a used compressor on CL?ThanksLast edited by medicineman; 03-15-2012 at 07:45 AM.
Reply:Couldn't you get a bottle of nitrogen?  $50 a year or so for a lease, not sure what they charge for the gas but it is kind of a by product of getting oxygen out of the atmosphere.  That stuff is so dry race teams use it in their tires so the partial pressure of the water in normal compressed air doesn't mess with their pressures as temp goes up.  It doesn't seem common now but years ago plasma cutters were on carts with gas bottles weren't they?  Unless there is an error in my arithmetic a big bottle will last for close to 100 hours at the usage rate in post #1.  Perhaps those numbers aren't scfm like gas in cylinders is marketed.franLast edited by fran...k.; 03-15-2012 at 09:13 AM.
Reply:A large cylinder of air (air works far better in an air plasma torch for cutting steel as compared to nitrogen....bottle of compressed air have about 240 cubic feet). At 4.0 cfm flow rate....you could get as much as 61 minutes of cutting....but actually a bit less as there is a post flow after each cut for cooling the torch.For a Powermax30....virtually any compressor that can produce over 90 psi will allow it to cut. The cfm (or scfm....which is cfm at a particular pressure....such as 90 psi) rating of the compressor will determine how long the compressor can maintain the pressure. If the cfm rating at 90psi of your compressor is less than the 4.0 cfm @ 90 psi that the Powermax30 requires....then you will get relatively short cuts. If the cfm rating of the compressor is higher than the plasma...then you can cut continuously.I have used my Powermax30 many times in the field with a small compressor that was designed for nail guns. The compressor is rated at about 3.4 cfm at 90 psi, and has about a 3 gallon tank....I can cut continuously for a little over a minute before the pressure drops too low to satisfy the pressure switch in the plasma.When the pressure drops below about 85 psi with the Powermax30...it will simply stop the arc....and will not allow you to refire until the pressure is adequate again.There are tons of used compressors on Craigslist......Jim Colt Hypertherm Originally Posted by fran...k.Couldn't you get a bottle of nitrogen?  $50 a year or so for a lease, not sure what they charge for the gas but it is kind of a by product of getting oxygen out of the atmosphere.  That stuff is so dry race teams use it in their tires so the partial pressure of the water in normal compressed air doesn't mess with their pressures as temp goes up.  It doesn't seem common now but years ago plasma cutters were on carts with gas bottles weren't they?  Unless there is an error in my arithmetic a big bottle will last for close to 100 hours at the usage rate in post #1.  Perhaps those numbers aren't scfm like gas in cylinders is marketed.fran
Reply:A bigger tank means more cut time before the compressor pump kicks back on.  A bigger pump (bigger than the air usage by the tool/machine) means that the tank can refill faster.If you have a compressor pump with a CFM rating lower than the tool/machine needs, then you WILL 'run out of air'.  And then you have to stop and just twiddle your thumbs while waiting for the pump to refill the tank.Also, some pumps are not rated to be used continuously, ie they have a "duty-cycle" jsut like a welder or plasma cutter might have.  If you exceed (or try to exceed) the duty-cycle, the machine overheats and then either shuts itself down to protect itself (decent plasma cutters and welders usually do this) and you then twiddle your thumbs and wait for the machine to cool off, or like almost all air compressors which have no thermal 'safety' shut-off (except on the motor itself, usually) you end up overheating the compressor pump and then either have hot 'wet' air in the tank and going to the tool/machine using the air or the pump wears out prematurely or catastrophically (depending on just how hot the pump gets) or all of the above.The above mentioned and pictured Dewalt compressor can supply a PM30 just fine for almost any real-world usage (short of maybe trying to run the plasma continuously all day long).  Any compressor that is 'less' than that (in CFM) will end up making you wait for the compressor to 'catch up'.With an air compressor, almost no one ever say "Gee, I should have gotten the smaller one."  Trade-offs.  Pick where you are willing to compromise regarding the air compressor.  You don't need a 5hp 80 gallon two-stage compressor to run a PM30, but it would run it just fine (and let you run almost any other air tool that a 'home' shop would want/need, short of maybe some continuous use of a large/large sandblaster or some really air-hungry tools like maybe a die grinder or air sander).  A little 'pancake' or 'hotdog' air compressor that is typically used for a single nail gun will only let you make a relatively short cut before you have to stop and wait for the little pump to refill the little tank.  The best laid schemes ... Gang oft agley ...
Reply:I have a PM 30 and use a 15 gallon CH compressor in my garage. Since I don not make a lot of long cuts it has been fine. Tractor Supply has a nice single stage air compressor with a 26 gallon tank for $199.http://www.tractorsupply.com/jobsmar...ressor-1129132Probably not adequate for some members, but would work for what you are talking about.
Reply:Thanks for the clarification I was more used to cubic feet per hour like in oxy fuel stuff and a flowmeter with a little ball.  I do think a standard cubic foot is one at a certain pressure, not 90 psi.So the new plasma cutters at least for steel don't need dry air?
Reply:I'm not sure where you got the assumption about not needing dry air. Plasma cutters that use air....need clean dry air. Use of air with moisture content will shorten consumable life and can damage torch and air system components.SCFM generally means cubic feet per minute at 90 psi.Jim Colt   Hypertherm Originally Posted by fran...k.Thanks for the clarification I was more used to cubic feet per hour like in oxy fuel stuff and a flowmeter with a little ball.  I do think a standard cubic foot is one at a certain pressure, not 90 psi.So the new plasma cutters at least for steel don't need dry air?
Reply:Originally Posted by fran...k.Thanks for the clarification I was more used to cubic feet per hour like in oxy fuel stuff and a flowmeter with a little ball.  I do think a standard cubic foot is one at a certain pressure, not 90 psi.So the new plasma cutters at least for steel don't need dry air?
Reply:OK....I looked it up.SCFM is "Standardized Cubic Feet Per Minute. This means that:The air temperature must be 68 degrees Fahrenheit The relative humidity of the air must be 36% The air itself must be measured at sea levelThe compressor will provide the advertised amount of flow under the above conditions...and at an advertised pressue.So...if the compressor brochure says:3.7 scfm @ 90 psi......it will produce that much air flow on a 68 degree F day, with relative humidity at 36% and your elevation is at sea level.Jim Colt
Reply:Also SCFM is measure on the uncompressed air.  So 3.7scfm@90psi isn't flowing 3.7 cubic feet when it's at 90psi.  It's flowing 3.7 cubic feet after the 90psi air is expanded (and your barometric pressure is exactly 1 atm, and the air is at 'standard' temperature). Originally Posted by MoonRiseWith an air compressor, almost no one ever say "Gee, I should have gotten the smaller one."
Reply:Thanks for all the info.  I'm in South Florida so I'm at sea level but the humidity and heat are much higher than 68 degrees and 36% humidity.  I wish we had that type of weather, it would be nice.I think I got the answer from all you guys regarding the size unit I can use and or should use with my cutter.ThanksLast edited by medicineman; 03-15-2012 at 06:18 PM.
Reply:Originally Posted by assassin_worksto little !!! im using a CH that puts out 200 psi on a 15 gal. tank at3.7 cfm @90 psi  and i with the air force 400 i think it needs more cfm to keep it from making the compressor cycle so much