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## Air Compressors and Lurking!

 To: mgs@autox.team.net Air Compressors and Lurking! Sheldon_Kolansky@avid.com Tue, 10 Dec 96 12:23:30 -0500
 ```Personal and private to Dave Deutsch: (Call me a whimp will you! Call me a slimmy low life sewer lurker will you! Well I am a slimmy low life lurker and proud of it! I'll only put in my two cents when I have to (and when I have some time available). Just remember one thing Dave, I don't get mad I get even.) Back to reality. I have played around lots with air compressors and have fallen asleep many nights to drooling over WW Grainger's catalogues. The first and most important rule is you get what you pay for! First of all, HP numbers are the latest marketing persons guess of the day. A real horsepower is 746 watts, meaning at 110 volts it roughly 7 amps assuming a 100% efficient electric motor. I haven't seen any 100 % efficient motors lately. In reality you should figure about 9 amps per real HP at 110 volts. Halve that number if you are working with 220 volts. So my question is how do you get a 4 HP compressor to run on 110 volts (4X9=36 amps from your 15-20 amp outlet). (You don't) Second of all how many CFM's do you need at what pressure. The real thing you need from a compressor is CFM, cubic feet of air per minute at a certain pressure. For the same compressor, the CFM's go up as the required pressure goes down. (The compressor pumps air at about a constant volume. As it pumps more and more volume of air into a fixed volume tank, the pressure rises. As the pressure rises the compressor has to work harder. If you don't require the higher pressures, you get more air volume at a lower pressure) Determine what you want to do. Understand that serious sand blasting will run into serious \$\$\$. If you want to keep up to a sand blaster that has a 1/8" orifice, you better plan on 12 CFM at 90 PSI. You don't blast at 90 (at least I don't) I ran a 7-8 CFM blaster from my real 2 HP compressor steady state at about 60 PSI (the specs said the compressor would do 6.7 CFM at 90 PSI). A compressor rated at 125 PSI tends to run between 90 and 125 as the compressor cycles on and off. This means that you can only count on 90 PSI for your tools. If you buy expensive efficient tools you will get plenty of power. If you buy cheap, excuse me, inexpensive, tools like I do, then your power will be limited by the lower pressure. The storage tank is also a trade off. A small tank means you don't have to wait as long for pressure when you first turn it on. It also means you will run out of air faster if your compressor can not keep up to what you are doing. I.E. If you are blasting at 12 CFM and your compressor is good for 7 CFM, you can blast 3 times(about) longer with your 60 gallon tank than with your 20 gallon tank. Just remember that it will take 3 times longer to get the 60 gallon tank up to pressure than your 20 gal. A two stage compressor, is more expensive, but provieds up to 175 PSI. That really makes the inexpensive power tools go. I can't explain why, but the two stage compressors provide more CFM per HP than single stage units. Expect to pay \$300-400 for a real 5 HP single stage and \$800-1300 for a real 5 HP two stage. For serious sand blasting I would recommend a 5HP two stage compressor. For work other than sand blasting I would recommend a real 2 HP compressor with about 6-7 CFM. Smaller than 2 HP would limit the power tools that could be used. I now have a 5 HP compressor that draws about 21 amps at 220 volts (more than the central A/C on the house) and provides about 16 CFm at 175 PSI. Flames to /dev/null (except for David) Sheldon ```
 Current Thread Air Compressors and Lurking!, Sheldon_Kolansky <= RE: Air Compressors and Lurking!, Randy Rees Re: Air Compressors and Lurking!, W. R. Gibbons RE: Air Compressors and Lurking!, Wayne Kube RE: Air Compressors and Lurking!, Sheldon_Kolansky