On the SEARS units, agreed best to stay clear of them and those
"odd ball" horsepower ratings. On the rec.woodworking newsgroup
some time back was a good explanation of PEAK power, right at
STALL, being something like 2.5 times the usable power... which
is what SEARS used to come up with those labels.
My 20 year old Sears compressor is rated at 4 hp, with a large 220v
(15amp) motor on it. It does manage to put out enough to run an air
sander, or paint a car... but the 20 gallon tank runs down and takes
a bit of time to refill... which is a pain when sanding and I want
to get the job done.
Another thought: (haven't done it), but is to use a surplus A/C
compressor with the 12V clutch. Sketchy details were given in
"Projects in Metal" about a year back. Idea is to let a 220V 4hp
motor come up to speed, then the A/C clutch is controlled by pressure
switches. Obvious the motor would be running full time, but since I
would like to have a "3 phase idle" motor for my lathe & milling
machine, really not too bad of an idea (just let it idle when using
the machining tools... or power the compressor as needed). [I think
Met-Lab series of 'contruction projects' also outlines the same
thing. Plans cost $4]
DRAIN: angle the horizontal feed line, to help with draining. Having
the air line "T" into a vertical section of pipe, the lower 3' having
a drain on the bottome will help with moisture.
NOSE: Best if you can mount the compressor in a "service room" of a
large shop. I've also seen boxes, in the main shop area, around the
compressor. Interior lined with cardboard egg cartons, and still a
large 1' gap at bottom and top, but did help soften that NOISE. ;-)
Easy access to the bottom drain valve is always a good idea.
Tempted to have a electric soleniod on the thing, so I don't have
to crawl on the floor every half hour for draining the tank during
high humidity days.)
Tom Walter '67 & '68 Datsun 2000
Austin, TX. '71 & '72 Datsun 510's