Teach me about compressors

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I am a hobbyist welder wanting to step up to a plasma cutter.  I am looking at the Hypertherm PM45.  I have a Sears Craftsman 12 gallon compressor that has served all of my needs in the past that was given to me as a gift so I really didn't have a choice in what I got....needless to say I got it.  Reading the requirements on the PM45 says I need 6cfm @ 80psi for cutting.  The compressor I have is rated at 2.4cfm @ 90psi and 3.7cfm @ 40 psi.  I was under the impression that is the rating on the pump itself and not the output from the tank.  Am I correct to believe that I will be able to run the PM45 for roughly 40 psi of air from the tank (max pressure is 125psi) before the air will be insufficient or is the cfm rating on my compressor the actual output rating from the tank and not the pumps rating?If this compressor won't give me the output to run the PM45 at all is there anything I can do to the compressor itself to "up" the ratings where the PM45 would be usable with this compressor without having to buy an entire new compressor?  Perhaps another tank tied in?  Carpenters on our jobsites run an "air keg" which basically piggy backs off their gas driven compressors for air storage.  Would something like that help?I am definitely not wanting to buy a new compressor on top of a PM45, if it comes down to that I will be buying another rifle instead of the PM45Thanks in advance.
Reply:I am also a hobbyist so I can't go into any details but as far as I know your setup will work as long as you have the required PSI in your tank.  So if you charge your tank to 125 psi your plasma cutter will work until it drops below 80 psi.  Your compressor should kick on before that and this is where your going to have your problem.  Your compressor won't be able to keep up with the draw of the plasma.  How long it will take to drain your tank I don't know.  If you are doing small cuts or don't mind waiting for the pressure to build back up inbetween cuts then you can get by.  You can upgrade your compressor so it will keep up with the plasma gun or add tanks so it will take longer to drain down to 80 psi.  But if your adding tanks you will have to wait longer to fill them because of your small compressor.
Reply:With your existing compressor, you are correct in your reasoning that you would only be able to make a short cut before the air supply can no longer give enough air to the plasma cutter.IMHO, unless you are making just very few very short cuts and can wait after each one for the tank to refill before making the next plasma cut, your existing air compressor will drive you crazy with the very short cuts and the waiting to refill.  Remember that the plasma cutter will start drawing air as soon as you pull the trigger on the torch, but will continue for a bit after you release the trigger for the post-flow cool-down air.  If you 'run out' of air when the machine is trying to do the post-flow, you end up chewing up tips and electrodes from the plasma cutter.  Something to do with that 10,000F+ degree hot plasma flowing through those little itty-bitty copper alloy pieces in the torch.  The post-flow cool-down air is kind of important there.YMMV and you may have more patience.If you add another air tank into the 'system', yes you could get a bit more time of cut before you run out of air.  But you will be waiting even longer for the (small) air pump to refill the (now larger air storage) tank(s).  And the 'small' air pumps are usually 'balanced' as to their size/capacity to match the size/capacity of the air tank.  Try to use a 'small' pump to fill a 'big' tank, and you might overheat (and thus 'burn up') the pump because you are exceeding the original duty-cycle of the pump.Tank size/capacity (volume of tank x pressure in tank) gives you a 'burst' of air, pump capacity gives you 'sustained' air usage.The 'burst' of air scenario would be something used intermittently that pulls a big glob of air.  Like an impact wrench.  Use it for a few seconds until the fastener is on/off, and then the tank refills while you move over to the next fastener.The 'sustained' usage is for something that needs air over a longer (sustained) period of use.  Like a paint sprayer or a die grinder or an air sander.  The tool is used for more than just a few seconds at a time.My opinion?  Save up some bucks and get an air compressor that has a bigger tank and a bigger pump (or another air compressor that is combined with your existing one to give you the minimum 6 cfm the plasma needs to run and plumb the two systems together).  You can do soooo much more with air tools when you have the air supply to 'feed' them.  The best laid schemes ... Gang oft agley ...
Reply:With about half the required air delivery and a 12 gallon tank I'd say you are SOL."USMCPOP" First-born son: KIA  Iraq 1/26/05Syncrowave 250 w/ Coolmate 3Dialarc 250, Idealarc 250SP-175 +Firepower TIG 160S (gave the TA 161 STL to the son)Lincwelder AC180C (1952)Victor & Smith O/A torchesMiller spot welder
Reply:Brent has it about right on this subject, what you are needing is the volume to supply the plasma and that is provided by the tank size. In your case 12 gallons isn't going to last long enough to do much cutting. If you could add a larger tank, say 70-80 gallons then you could cut for a bit longer, but still have to wait for the little compressor to catch up again. You could get by a little cheaper by buying another compressor of about 4-5 cfm to add to the 2.6 you have now to give you the 6 cfm the plasma requires(with a little extra). You don't neccessarily have to have one compressor suppyling all the air, just combine the output of two to equal the flow you need. You could go with a 20 gallon tank and the 4-5 cfm compressor and plumb them both into that tank to get the volume you need. Doing this will allow you to use just one compressor for most of your needs, then kick on both for when you need the added volume. I have several compressors myself that I combine the airflow when I need to. I converted a 25 gallon propane tank for this purpose, with fittings to have 2 compressors feeding it and an outlet to whatever I am powering. I also made some adaptors to be able to plug in more compressors to the 2 inlets to the tank to REALLY blow some air.
Reply:I got a 60 gal, single stage Sanborn 6HP vertical in 1994 and it was great until I started sandblasting. Totally inadequate. It would be the same for my Hypertherm 65. So a few years later, I ADDED a Campbell Hausfeld 60 gallon 6HP vertical and plumbed them together so they share tanks and pumps. Never looked back. To this day, its more than enough for anything used in a one man auto restoration shop from sandblasting to plasma cutting, to painting. It was a very cheap way to solve this problem with the only drawback being the space two compressors take. I built a closet for them using soundproofing and now a person hardly knows they are there. Hope this helps.
Reply:In the grand scheme of things compressors are cheap! Granted I got mine used but I have an 80 gallon that keeps up with everything I have in the shop no problem including the blast cabinet and plasma.
Reply:The key with compressors is not so much the size of your tank, it's the size and type of air pump. If your using large volumes of air, you need a dual stage pump (dual stage is not to be confused with dual cylinder). This type of compressor makes much more compressed air than a single stage pump. They also run cooler. They make compressed air with the piston at the top and bottom of the cylinder, not just at the top.The size of the tank is the next thing to consider. Bigger is better, as long as you have the proper type of pump to fill the tank without ruing too much and creating too much heat. Too much heat = water (condensation) when the air cools.Inter coolers (air cooling between cylinders) and after coolers (air cooling before the air goes into the storage tank) help increase the efficiency and longevity of the good compressors.Last edited by snoeproe; 04-11-2013 at 11:21 PM.JasonLincoln Idealarc 250 stick/tigThermal Dynamics Cutmaster 52Miller Bobcat 250Torchmate CNC tableThermal Arc Hefty 2Ironworkers Local 720
Reply:Originally Posted by snoeproe If your using large volumes of air, you need a dual stage pump (dual stage is not to be confused with dual cylinder). This type of compressor makes much more compressed air than a single stage pump. They also run cooler. They make compressed air with the piston at the top and bottom of the cylinder, not just at the top.
Reply:I use my PM45 on a Craftsman 4HP 25 gallon tank compressor supplying 7 scfm at 90 psi and it barely keeps up.  You're gonna need to go big or go home.TA Arcmaster 300CM3XMT 304S22P12 suitcase feederX-Treme 12VSOptima pulserTA161SMaxstar 150STLHypertherm PM45OP setupStihl 020AVP, 039, 066 Magnum
Reply:Originally Posted by KavallYou've got that wrong. Two stage air compressors have a 1st stage cylinder compressing the air to an intermediate pressure then it passes from that cylinder into a 2nd stage cylinder where it is pressurized to final pressure. Often there's a intercooler in between the two stages. Single stage air compressors hit their "full" pressure on one stage. They typically produce higher CFM however are typically limited to 150PSI.
Reply:Higher psi in the pressure vessel means more volume in the pressure vessel.
Reply:Originally Posted by Drf255I use my PM45 on a Craftsman 4HP 25 gallon tank compressor supplying 7 scfm at 90 psi and it barely keeps up.  You're gonna need to go big or go home.
Reply:But wait, there's more! Don't act now.....Another option is using a high pressure cylinder filled with air. You can get cylinders with 4,500psi, use a regulator to get your 80psi out and use a small expansion tank.Scuba tanks or air tanks from your lws. Just another option.Lincoln Power Mig 210MP MIGLincoln Power Mig 350MP - MIG and Push-PullLincoln TIG 300-300Lincoln Hobby-Weld 110v  Thanks JLAMESCK TIG TORCH, gas diffuser, pyrex cupThermal Dynamics Cutmaster 101My brain
Reply:But dont forget your air drying system either. More money to do a good job.Lincoln Power Mig 210MP MIGLincoln Power Mig 350MP - MIG and Push-PullLincoln TIG 300-300Lincoln Hobby-Weld 110v  Thanks JLAMESCK TIG TORCH, gas diffuser, pyrex cupThermal Dynamics Cutmaster 101My brain
Reply:Originally Posted by Joker11But wait, there's more! Don't act now.....Another option is using a high pressure cylinder filled with air. You can get cylinders with 4,500psi, use a regulator to get your 80psi out and use a small expansion tank.Scuba tanks or air tanks from your lws. Just another option.
Reply:Originally Posted by Pete.S.But a regular sized scuba tank is 80 cuft. If you need 6 cfm it's only going to last you about 13 minutes. Doesn't seem like much but perhaps that's enough?
Reply:never mind scuba tanks, that's for making 1 small cut in the middle of the jungle when you have no other way. Get a compressor that will put out in the neighbor hood of 15 CFM minimum 18-20 is better. Remember with a plasma the thicker the material, the slower the travel speed the more air your gonna need. You want play/ you got pay. plan on $1000 for the home chepo, 1500-2grand for quality, quality will last your life time if you maintain it. Also will need 220volts,40-50 amps to run it as well."Si Vis Pacem Para Bellum"Lincoln Idealarc 250 AC/DCMillermatic 251   Syncrowave 300   30A spoolgunLincoln MP210Hypertherm 45(2) LN 25(2) Lincoln Weldanpower 225 CV(4) SA200   1 short hood    SA250    SAM 400
Reply:And another 40-70 amps for the plasma. Better leave the lights off when you make a cut on a 100 amp service.
Reply:Originally Posted by VPTAnd another 40-70 amps for the plasma. Better leave the lights off when you make a cut on a 100 amp service.
Reply:I got one of these the other week:http://www.lowes.com/pd_54284-1126-VT6362_0__It's made by Campbell-Hausfeld.  They have the same one at Wal-Mart in blue and it says Campbell-Hausfeld on it and it's $50 less.  11.5 SCFM @ 90 PSI and draws 15 A.  I made a 10 ga extension cord and run it off my 30 A dryer outlet (literally - I made a 3" hole in the ceiling of the garage that goes up into the laundry room  ).  Keeps my 50 A outlet open for plasma or a welder.
Reply:I'm also shopping for a quality, American made air compressor to run my plasma, sand blasting cabinet, and various air tools. These are the two companies I've researched. Curious if anyone here has any feedback on them?Eaton:http://www.eatoncompressor.com/page/page/504747.htmCAS:http://www.compressed-air-systems.com/Thanks!GarLincoln Electric, Power MIG 256Hypertherm Powermax 45 Miller Dynasty 280DXSmith O/A torchGenesis of a welding table
Reply:While you didn't ask this question, I feel the need to offer the answer. Make sure you have a good air drier/cleaner in place. Moisture, oil, and dirt in your air will make it difficult to make a good cut and will cause premature wear to the consumables on the plasma torch.Lincoln Idealarc 250Lincoln Weldanpower CC/CV engine driveLincoln LN-25 wire feederMiller Syncrowave 180 SDVarious oxy-fuel setups featuring Victor, Harris, and Prest-o-lite products
Reply:Originally Posted by moya034While you didn't ask this question, I feel the need to offer the answer. Make sure you have a good air drier/cleaner in place. Moisture, oil, and dirt in your air will make it difficult to make a good cut and will cause premature wear to the consumables on the plasma torch.
Reply:pre-filter before dryer = SMC AF40-N04-Z (5 micron):[ame="http://www.amazon.com/SMC-AF40-N04-Z-Compressed-Particulate-Polycarbonate/dp/B0078SEE90"]http://www.amazon.com/SMC-AF40-N04-Z-Compressed-Particulate-Polycarbonate/dp/B0078SEE90[/ame]dryer = Ingersoll-Rand D18IN:http://store.industrialairpower.com/..._p_211042.htmlIAP has a generic pic on their website.  It actually looks like this (shown with my old compressor): Attached ImagesThere's the Harbor Freight dryer too:http://www.harborfreight.com/compres...yer-40211.html
Reply:Originally Posted by GarSounds good.  Which air drier/ cleaner are you currently using?  And which plasma torch are you using?Thanks!Gar
Reply:Am I the only one who has notice that horsepower ratings on compressors are BS? My craftsman compressor sitting outisde claims to be a 5 HP, but it's a 110v 15 amp unit. Last I check 110v at 15 amps only gets you 1.8 HP.What gives? Is this marketing lies or is there some weird way that air compressors are rated?If I got a compressor running a "real" 5 HP 3 phase motor, how much CFM could I expect to get out of it? (5 HP is the biggest motor my RPC can handle, even tho it can take a total of 15 HP)Lincoln Idealarc 250Lincoln Weldanpower CC/CV engine driveLincoln LN-25 wire feederMiller Syncrowave 180 SDVarious oxy-fuel setups featuring Victor, Harris, and Prest-o-lite products
Reply:Originally Posted by moya034Am I the only one who has notice that horsepower ratings on compressors are BS? My craftsman compressor sitting outisde claims to be a 5 HP, but it's a 110v 15 amp unit. Last I check 110v at 15 amps only gets you 1.8 HP.What gives? Is this marketing lies or is there some weird way that air compressors are rated?If I got a compressor running a "real" 5 HP 3 phase motor, how much CFM could I expect to get out of it? (5 HP is the biggest motor my RPC can handle, even tho it can take a total of 15 HP)
Reply:Horsepower & CFM:  http://www.truetex.com/aircompressors.htm"USMCPOP" First-born son: KIA  Iraq 1/26/05Syncrowave 250 w/ Coolmate 3Dialarc 250, Idealarc 250SP-175 +Firepower TIG 160S (gave the TA 161 STL to the son)Lincwelder AC180C (1952)Victor & Smith O/A torchesMiller spot welder
Reply:Originally Posted by ProCharger  Thanks for all of the replies, you made my choice much easier.  At the moment I really don't want to upgrade compressors AND spend the coin on the PM45.Rifle it is!
Reply:700 sps tactical aac-sd in an accuracy international aics 1.5 chassis. Gonna go with badger rings and bases and probably a 6-24 vortex pst or razor hd scope. I wish I had the coin for an accuracy international ae mkII but then I would be dreaming. Damn gun by itself would run me more than a complete setup ready to hit the range.
Reply:...a more satisfying purchase IMO.  Get the Vortex PST.  I have Vortex optics on most of my rifles.  Leupy on everything else and one S&B.My 338 Lapua has a 6.5-25x50 PST and it's very discernable past 1500 yards.
Reply:Need I say more?   Attached ImagesLincoln Electric, Power MIG 256Hypertherm Powermax 45 Miller Dynasty 280DXSmith O/A torchGenesis of a welding table
Reply:Originally Posted by GarNeed I say more?
Reply:S&B are too heavy for their size, you need really stout rings to handle them on some rifles. Particularly light weight magnum rifles. Talley refused to make a set of rings for one of S&B's scopes a couple years back because of it. Rolex and their mechanical watches are inherently more inaccurate than any quartz movement watch. I'm a huge fan of mechanical watches, but it is funny that cheap quartz watches are many times over more accurate.
Reply:Originally Posted by SidecarFlipYes, large wallet and status symbol.  Considering it's a 4500 dollar optic, there are lots of contenders at a lower price point, Vortex is one.Maybe I can't see all that well anymore but I can bench my S&B and a Vortex and a Mark4 side by side and I can't discern any difference in image quality, brightness or adjustability.  I can, however, discern a vast difference in price.I have a Rolex too.  People say you can have a Timex and it's just as good.  Both tell time and both will be right 2 times a day, even if they don't work, however, a Rolex is a sign that you've arrived financially just as an S&B is.When I see a rifle with an S&B in the rings, I assume that either the owner is upwardly mobile, has good credit or is a poser.  Same applies to a Rolex.However, everyone looks about the same taking a dump on the porcelain god.
Reply:........."Interesting fact: In 2011 Schmidt & Bender won a $34 Million U.S. military scope contract (good till 2016), to be used by SF for the Army, Navy, Air Force, and Marine Corps".........Not at all suprising to me.  After all, the government in general has no issue with unregulated spending of funds they don't earn, In other words...., taxes..   What I do fined interesting is, is that S&B's aren't manufactured here, represented here but not made here and the Fed has a domestic buy policy.  I ought to know, my spouse is a high ranking DOD employee.Of course that could be that S&B's will appear as surplus goods at some point in the future.  Might be good for me.  I'm on the government approved bid list for various hard goods.