Replies

1. 
   mudman | Jun 11, 2006 07:49am | #1

   Any of the brands you mention are good enough for a home shop, and even a small comercial shop. Don't focus on the HP ratings, look at the amperage of the motor (much more accurate) and the CFM ratings. Get an oil filled unit, they last longer and run a lot quieter. Cast iron heads are prefered but may be out of your price range. Most of the house brand pumps are made by the same manufacturer. I like the waranty, and the bring it back for a return policy that the big box stores offer, including Sears. From the sounds of it you dont need a Puma or IR quality machine, those cost a premium but can handle continous duty, day after day use.

   Pardon my spelling,

   Mike

   Make sure that your next project is beyond your skill and requires tools you don't have. You won't regret it.

2. 
   LeeGrindinger | Jun 11, 2006 05:37pm | #2

   Yup, it's terribly confusing. Compressor ratings come in several terms. SCFM and CFM are interchangeable. SCFM means Standard cubic feet per minute, CFM means cubic feet per minute. "Displaced air" is the amount of air the compressor sucks it, "delivered air" is the volume of uncompressed air coming out of the line. Higher end compressor lines will make these terms very clear. Home Depot lines will lie to enhance their numbers.

   You'll see numbers like 5 CFM@ 80 psi. What this often means is that the compressor will suck in 5 cubic feet of ambient air and compress it, not that you'll have 5 cubic feet of 80 PSI air. Most CFM ratings are displaced air ratings, what the compressor sucks in. Due to leaks and inefficiencies most compressors struggle to meet 60% efficiency in higher pressures.

   So, 5 CFM @ 80 PSI does not mean you get 5 cubic feet of air compressed to 80 PSI. We live at around 14 PSI so no compressor starts at 0.

   Be wary of ratings that state "delivered CFM" because they are measuring the volume of air after it is uncompressed and this could very well be a lie to enhance their numbers, especially in the cheaper brands. Don't think that someone's ratings are phenomenally better than someones else's when amperage is similar, they have manipulated the CFM ratings.

   The good news is that most tools are now rated the same way so if you buy a tool that needs 3 CFM @ 80 PSI look for numbers about 25% higher in the compressor and you're most likely covered. No compressor motor and head are rated for continuous duty so buy a machine at least 20% beyond your anticipated needs, most are rated at around 80% duty.

   So, go shopping but compare CFM and amperage. Amps are the only true measure of motor size these days since horses started getting so much smaller. HP ratings are often taken during motor start-up, when both coils are pulling amps, once the starter coil kicks off the true ratings appear but these are not as flattering to small motors.

   Shop amperage and CFM ratings. If you need a high volume of 80 PSI or higher get a 2 stage compressor head, it's far more efficient to compress air with two heads, one made for each stage of compression.

   Lee

1. 
   frenchafry | Jun 11, 2006 07:13pm | #3

   Very good information..thanks.

1. 
   LeeGrindinger | Jun 12, 2006 01:47am | #4

   You are most welcome,Lee

3. 
   mapleman | Jun 12, 2006 05:30am | #5

   French,

   I have a 30 gallon husky (home depot) compressor, belt drive, cast iron head. It is very quiet compared to the last (oil-less Sears direct drive) compressor I owned. I planned to argue Mr. Grindinger's point that home depot will lie about their compressor ratings, but after I went to the shop to double check (good thing I did before I put my foot in my mouth) I discovered he was absolutely right! In very small letters above the HP rating it says "peak". So small I never noticed it before. Also, I decided to check the HP rating on the motor (Doerr, made by emerson electric) and it says - get this: HP - special! No numerical value whatsoever. Mr Grindinger, sorry I doubted your wisdom. My next compressor purchase will not be a husky unless they start shooting straight. I can say, though, that after 3 years of pretty regular use, I haven't even had to add so much as a drop of oil to the pump - and never a problem with it that I can remember.

   Lee

1. 
   MrBill | Jun 12, 2006 05:58am | #6

   Lee,

    Almost all tool manufacturers, from compressors to vacuum cleaners, use the same "peak" HP ratings that do not mean a thing. So its just not Husky that you will have to boycott !

    The true test of a compressor should be the CFM rating. As far as I know, the CFM rating should be "delivered", meaning that the compressor will deliver 3cfm (or whatever number) of air at 80psi without running out of air.  If yo know the CFM rating of the tools that you will be using, you should be able to figure out the compressor you need. The Sears tool catalog used to have a chart showing the tools, how many CFM of air they needed and the compressors and what they would supply.

   One thing I will say for sure, get the biggest one you can affors, you will always find more uses for it !

   Hope this helps,Bill Koustenis

   Advanced Automotive Machine

   Waldorf Md

1. 
   frenchafry | Jun 12, 2006 06:05am | #8

   Mr. Bill...take a look at message #30345.3...it will make you not trust cfm either. what a twisted world we have...lol

2. 
   LeeGrindinger | Jun 12, 2006 02:23pm | #9

   I can assure you, Bill, that delivered air is measured at ambient (uncompressed) pressure which is around 14.7 PSI.Do the math to get the volume of air a compressor would need to suck in to get the numbers. Let's say 5 CFM @ 80 PSI80 PSI divided by 14.7 will give you the number of cubic feet of ambient air needed.Times 5Plus 40% for inefficiencies and leaks,Right near 38 CFM needed to produce those numbers. Hold your hand over the intake to your compressor, you'd feel the wind rush by, there are vacuum cleaners that don't have that much draw.If you want the truth don't talk to salesmen, I've yet to meet a salesman that understands these numbers. Talk to the engineers. Call Ingersoll Rand or another top commercial brand and ask for an engineer, tell them you're doing an article or something.Hey, I'll be gone for a couple of days, see you on Wednesday,Lee

1. 
   mudman | Jun 12, 2006 05:14pm | #10

   I was about to call B.S. on the method of CFM you propose. But now you got me wondering, sounds like you know what you are talking about.

   So, if I have a tool that requires 6 CFM @ 90 PSI will a compressor rated at 6 CFM @ 90 PSI run it? In other words are the tools rated the same way as the compressors? If so then all is equal.

   MikePardon my spelling,

   Mike

   Make sure that your next project is beyond your skill and requires tools you don't have. You won't regret it.

1. 
   LeeGrindinger | Jun 15, 2006 12:27am | #13

   Yup, the tool dealers know they will price themselves out of the market if they give numbers drastically different than compressor manufacturers.If you think of it in terms of 6 CFM of ambient air delivered at 90 PSI you will be on the right page. In fact, 6 CFM of ambient air compressed to 90 PSI only takes up about one cubic foot when it's held at 90 PSI. Make sense? The only issue you might have is duty ratings. No motor driving a compressor head is rated for continuous duty, they need to rest and cool off as do the compressor heads. Hence my suggestion that you buy a compressor rated for 20% more than your needs.Lee

2. 
   LeeGrindinger | Jun 15, 2006 01:34am | #14

   I should just add,Cheap lines like Coleman and Husky and other Home Depot brands often rate CFM by displaced air. This means that the numbers will be roughly 40% higher than delivered air and this could really mess you up if you buy based on numbers between tool and compressor being too close.Lee

3. 
   mudman | Jun 15, 2006 06:02am | #15

   Thanks for the info. Definately gives me a lot to think about.

   MikePardon my spelling,

   Mike

   Make sure that your next project is beyond your skill and requires tools you don't have. You won't regret it.

4. 
   LeeGrindinger | Jun 15, 2006 07:45pm | #16

   You're welcome,Anytime you want to call BS on me shout it from the mountain tops, I've fooled people smarter than you, Hah, hah, ha...,Lee

5. 
   mudman | Jun 16, 2006 05:32am | #17

   LOL

   I would never challenge the wisdom of someone of your obvious omnipotence.

   Except for the thread last week.

   LOL.Pardon my spelling,

   Mike

   Make sure that your next project is beyond your skill and requires tools you don't have. You won't regret it.

2. 
   Scarecrow | Jun 17, 2006 01:09am | #19

   just a nit.  Most pressure gages read in PSIG, G meaning gauge, meaning that 0psi takes into account your ambient air pressure. 

    You can for specific purposes get gages that read PSIA,  A meaning Actual pressure but those are mostly used in labs and or environments/processes that are very pressure sensitive.

   If you live at high altitude 14.7 is not your local ambient air pressure.  Doesn't mean much for compressors but it sure does for vacuum.  The only thing it will do to your compressor is make it work harder to deliver the gage pressure you desire.

   There is quite a complicated formula to convert Actual SCFM to Demand SCFM.

   But you are coreect that the CFM quoted on most units is the Capacity SCFM (at the inlet not the outlet).

   Only two things money can't buy, True Love and Home Grown Tomatoes...Misty River Band

   Edited 6/16/2006 6:35 pm by Scarecrow

1. 
   LeeGrindinger | Jun 17, 2006 01:31am | #20

   Pick your nits if you want to, Scarecrow. 14.7 is a pretty handy number if you want to express how many cubic feet of ambient air it takes to make 90 PSI compressed air. I suppose I could list values for all altitudes above sea level but I'm just too lazy for that, I'll leave it to you.Lee

2. 
   frenchafry | Jun 12, 2006 06:01am | #7

   Thanks Lee...I also found out that the old ratings for HP were derived by cranking th motors up to destruct and measuring th HP at that instant...clever rascals. So you only get the rated HP once. In raeality the amps tell you much more as Grindinger stated. Now I have to decipher the ratings on pump heads ...they too are misleading. Thanks guys.

3. 
   HowardAcheson | Jun 16, 2006 09:12pm | #18

   >> and it says - get this: HP - special! Yes, the motor manufacturer do not want to put the real horsepower as it will conflict with the marketing horsepower used by the compressor manufacturers. But, they don't want to lie either. A point to keep in mind is that the motors used for compressors need to be a little different from ones used on many tools. With a compressor, the motor must be able to produce full power immediately to overcome the compression resistance of the compressor. With most other tools, motor start with no real force to overcome.Howie.........

4. 
   BillPentz | Jun 13, 2006 08:13pm | #11

   I had an old sears oil bath compressor that served me well for nearly thirty years when it finally died. I was good about emptying the water build up, but the tank was still so old and rusty inside I did not want to risk a rebuild.

    

   My next door neighbor owns a commercial compressor shop and regularly entertained me with air compressor stories. He shared one where a fellow failed to drain his tank, the bottom rusted and blew all at once pushing the whole compressor through the ceiling, rafters and into a roof. His saddest story happened a few years back to him personally. He had a well loved old hose and had been blowing out his garage when he got interrupted. That hose blew while he was inside and by the time he got back to his garage the heavy blower nozzle on that ruptured hose had beaten his two week old truck to the point the insurance company called it a complete write off.

    

   Anyhow his advice to me was take a very serious look at the Ingersoll Rand Shop Mate air compressors. Those have a reputation for being solid, quiet, and long lived, plus put out quite a bit of air. With his blessings I instead opted for the larger 80 gallon two stage from that same vendor. It took some work, but I found some pretty good buys online for the Shop Mates. I recall Northern Tool, and even Home Depot would let me order one. I don’t see those at HD any more so they might no longer stock them. Still, with the 20% off coupon that is a pretty good deal.

    

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   Edited 6/13/2006 1:40 pm ET by BillPentz

   
   

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   Edited 6/13/2006 1:41 pm ET by BillPentz

1. 
   frenchafry | Jun 14, 2006 12:25am | #12

   OK..thanks..I'll definitely look them up and check with HD.