"Craig D. Niederst" <niederst@telerama.com> wrote...
<snip>
>Features 135 psi, 8.6 scfm at 40 psi and 6.4 scfm at 90 psi air delivery,
>oil free design, 6 hp direct drive
<snip>
>Sale $279.97
This is at best a 2-3 HP air compressor. Many of these mass marketers
(including the well-known specialty tool catalogs) quote these inflated
horsepower numbers, but they're usually termed "developed horsepower" or
some other code word that basically means "inflated number". A real measure
is amperage - a 2HP electric motor should draw somewhere around 12 amps at
208 volts, about double that at 110 volts - this is off the top of my head,
but it's close. (Dave Massey and the other EE's, please help me out
here!!).
Industrial compressors generally quote "free air" figures - about 7 SCFM
from a 2HP compressor. Single stage compressors actually give you more free
air, but only give maybe 80-100 PSI working pressure. Two-stage compressors
give a little less free air (because of the additional pumping losses) but
give a higher working pressure. Either one is OK for what you want to do,
but sometimes you may want to blast at higher pressures, and you'll have an
easier time with a 2-stage unit.
Sandblasting -- If your motor is too small, you'll only be able to blast for
a few moments and then have to wait till your air tank refills. If you
don't mind "Chinese water torture", you CAN blast with a too-small
compressor. Everything is relative - 1 HP won't get it under almost any
circumstances, 2 HP is slow, 3 HP keeps up mostly, 5-6 HP can really get the
job done.
In any case, buy motor amperage - not quoted HP.
Karl
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