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  • FusionManiac
    started a topic Sizing a shop compressor

    Sizing a shop compressor

    I have searched for a post from several months ago that gave a real lucid discussion of sizing a compressor for the shop and went into the falacy of manufacturer's horsepower ratings. I think it was in response to a query about supplying a plasma cutter, but I'm not positive. I wish that I had saved the link to that page cause I can't find it now. Does anybody remember posting or reading something like that?

  • davinci2010
    replied
    The real way to tell the real world output of an air compressor is cfm. Look for how many cubic feet per minute it puts out at the pressure you will be working at. This is what air tool / equipment manufacters use to tell you what their product requires. Horsepower of the compressor is less relevant, because most manufacters are lying about what their products put out. A real 5 horsepower industrial compressor puts out around 18 cfm. A genuine 7.5 h.p. puts out around 22-25 cfm. If you are limited to single phase power, 7.5 h.p. is about as big as you will be able to run. The blast cabinet is going to use the most air in your shop and a 7.5 h.p. two stage compressor with an 80 gallon tank would do the trick. Quincy, Champion, and Saylor Beall are good heavy duty units. My 2 cents as I used to be an air compressor tech.

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  • FusionManiac
    replied
    Bigger is better until it gets to be too big and the excess capacity sits wasted. I have neither the space nor money to buy a unit that is bigger than I will ever use in a single person shop.

    Typical maximum uses I might have are power tools, plasma cutter and small blast cabinet. I might do the occasional painting job. I can't think of any other high pressure/high volume tasks I might come up with, but I'm pretty sure there are some. The past discussion I was looking to find again was in regards to the manufacturers ratings and how to calculate the real output of a compressor in everyday use.

    There must be a narrow range of psi/cfm that works in 90% of small shops. I read all the time about people who bought a compressor, only to find out that it doesn't meet their needs. I hope to avoid that with the help from folks here.

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  • con_fuse9
    replied
    Singe stage vs. Dual Stage

    As everyone has mention, bigger is better.

    Dual stage pumps are usually capable of going to 175 psi. Basically one compressor cylinder feeds the one adjacent to it. However, you get less total CFM. If you need high pressure, its the only way to go. Makes your air storage last longer as well (more air at 175psi, vs 125 psi).

    Single stage will have higher sustained CFM.

    If you want the compressor to literally last forever:
    1) Cast iron pump - in 30 years or so you can actually rebuild it!
    2) Separate, belt driven setup. If the motor ever fails (big IF), easy to replace. Good motors will have manufacturer, case number, hp, and RPM listed. Manufacturer name isn't so necessary
    3) Remember to drain the tank regularly - maybe get automatic timer driven drain. The only thing that can kill a tank is rust on the inside.

    As for manufacturer claims. SCFM is supposidly CFM at rated pressure. That's OK.

    However a few years ago they started rating them "SHP" or "Developed HP" something like that. Basically 5and 6hp compressors running off of 110/15Amp plug. Yeah right. Most of these designs are "oil-less" and they are quiet but at the expense of performance. Unless you need the 'quiet' part, stay away from "Oil Less"

    Glancing at the Sears webpage it looks like they've gone back to 'running horsepower' which is a better comparison. 1.5hp is possible on 110V. 2.5 is not.

    Its tough to go wrong with Ingersal Rand. They are available in enough places to be affordable. I haven't bought a IR compressor in a while but they were always good quality units. If you pick carefully, you can also find acceptable units at the Sears / Home Depot / Lowes. If you are going for a more portable unit, look for 30gallon horizonal tank + cast iron pump.

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  • dondlhmn
    replied
    Air compressor sizing

    One thing seems to be true. For myself and all of the friends I have that use a blast cabinet in the shop.....BIGGER IS BETTER when it comes to picking out a compressor! No matter what the cabinet manufacturer says it needs, get one that is at least one size bigger. That danged cabinet can really use up the air, especially whan being used for long periods of time at a stretch as in when doing something you want especially/PERFECTLY clean. And I HATE waiting for the compressor to catch up......
    Last edited by dondlhmn; 05-25-2010, 11:00 AM. Reason: spelling

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  • Andy
    replied
    I was limited to 7.5HP and 24CFM since that's about the biggest I could run on single phase. I would also spend the extra money for the auto tank drain and the aftercooler. These seems to really work on getting the water out. I have a water separator after the tank, but before my distribution piping. I rarely get any water out of the separator. The aftercooler cools the air enough to make the most of the water fall out in the tank.

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  • ephotrod
    replied
    The biggest and baddest you can afford. A compressor is not like a women you want it big and heavy and with a cast iron pump, 2 stage.
    Josh

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  • davinci2010
    replied
    I can say absolutely, take the manufacterer's horsepower ratings with a grain of salt! Most ratings are inflated to an ideal or other unobtainable amount; Not what the motor really puts out on average. Look at the advertising for blankwaukee and blankwalt chop saws. 120 volts single phase, 15 amp current draw, 5.2 max. horsepower developed. Yeah right! Before the die hards speak up, you can even factor in watts drawn and watts output. Still does not add up. The Government had to step in when Detroit was pulling this, mabye it's time for another intervention.

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  • FusionManiac
    replied
    Originally posted by vin-man welding View Post
    That's not the discussion I am thinking about. Dang it!

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  • vin-man welding
    replied
    your answer:
    http://www.millerwelds.com/resources...ghlight=plasma

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  • Bob Miller
    replied
    7.5cfm

    I just ordered a Thermal Dynamics 152. It takes 7.5 cfm at 70 psi.
    In my shop I have a IR 5 hp T30. It will do everything I want except truck tires with a 1" gun. I have 12.5 hp Kolher/Champion (in pu) I belive It's rated 16 cfm and it will not do truck tires. What I mean is you have wait for recovery.
    The standup models take less foot print.
    My 4.5" hand grinder/sander will even keep my shop compressor working hard. Say you finish a project, now you have sand it and prep it for paint (all I work with is rusty iron).
    Most of my power tools are air.
    If I run the shop compressor every day my PG&E bill will be about 100 more a month.
    So I also have a Snap-on 1 hp that I use for small jobs every day,tires, air cleaners...
    BTW it will run my Hypertherm 900.
    Bob
    Last edited by Bob Miller; 05-23-2010, 08:33 AM.

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  • Pass-N-Gas
    replied
    My 20HP 3 Phase unit with a 120 gal air tank does the job for for me.. I can run the plasma, air tools, blast cabinet and all of the painting equipment I want..

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  • davinci2010
    replied
    You want to size a shop compressor by volume of output. Each of the tools you are using are rated in how many cubic feet per minute of air they require. Figure out what the air demand of the most tools you will be operating at one time is, then compare that to the tool with the highest air demand in your shop. For instance, you will be using both a die grinder and a chipping hammer with a combined air requirement of 25 cfm. You also have a 9" air angle grinder in your shop that needs 57 cfm. You will need a compressor that will support 57 cfm. As far as single and two stage compressors; If you run your tools at 90 lbs. then you will not notice a difference. If you run your tools above 90 lbs. you will notice a pressure drop while you're working, if you are running a single stage compressor.

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  • Scott Hightower
    replied
    Compressor Size for shop

    Not sure about the article you are looking for but I'll provide a few thoughts.

    For a plasma to work properly it is imperative to have enough volume of air. Check the demand on the nameplate of your model and add at least 20% extra to ensure you never run low. You should also have a large reservoir.

    If you are planning on some serious painting upgrade to a 5 HP minimum.

    Scott
    welders360

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