At 04:07 PM 9/5/02 -0400, Chris Thompson wrote:
>...
>I'm looking for an air compressor. I do remember someone, Barney I think,
>saying not to buy based off horsepower, but to buy off stated CFM specs at
>certain PSI.
Yup. Retailers and manufacturers lie a lot about motor power ratings these
days. Motors that are obviously no no more than 2 HP by the electrical
power consmption are often advertised with 5 to 6 HP ratings.
Look here for my crash course in Air Compressor Tech:
http://www.ntsource.com/~barneymg/mgtech/tools/compress.htm
>For example, Sears has a 60gal tank that will do 12.4 SCFM at 40PSI and
>10.2SCFM at 90PSI. Though $449 is a bit more than I wanted to spend. (That
>model is at http://u.st/?4790)
Well that URL brought up a Sears error message page. So much for Frames
and Javascript driven web pages. With a little searching I did turn up one
Sears compressor the fit your description:
00918419000
Use the URL above and then put this item number in the search box to go
directly to the product listing. But then the link from there didn't work
either, and I had to start at the header menu and go through Tools,
Compressors, Stationary Tank Compressors, and then the last item at the
bottom of the page. The final ULR looks like this:
http://www.sears.com/sr/product/summary/productsummary.jsp?BV_SessionID=@@@@2104361450.1031299904@@@@&BV_EngineID=ccgcadcgefdgjfdcehgcemgdffmdfil.0&vertical=TOOL&fromAuto=YES&bidsite=null&pid=00918419000
I looked for the electrical specs, but they refuse to disclose the running
current draw. All it says is 240 VAC - Hard wire only by a professional
electrician. This unit puts out about 35% more air than my 2 HP belt
driven twin cylinder unit. From that information and the largest picture I
could find I'm guessing this is about a 3 HP motor, with the 7 HP
rating. If you're still curious, look in their Glossary under "Maximum
Developed Horsepower" (and you still won't understand it).
I personally think it's a bit on the large side for a home shop, but if you
have the space and feel that you need that much air flow, then the price
isn't too bad for the size. At least it's a belt driven oil-type
compressor, so maybe it won't be too noisey.
>So, I have to ask the gurus, what are good flow rates?
For most home shop activities, 7 to 8 SCFM is enough. If you expect to be
doing lots of body work, and you like to use a circular air sander / body
grinder, then maybe you could use the larger compressor. For media
blasting the sky's the limit on air usage, but for home shop use you can
use appropriate blast nozzels that will limit air flow to about 6 SCFM. It
still works, just shoots a smaller stream and limits the productivity. You
wouldn't want to do a whole car body, but road wheels and valve covers are
fair game.
>What ranges should I be looking for?
Determine your tool with the largest air demand. That would be max air
flow times the duty cycle. (See URL at top of message). If it's more than
your planned compressor puts out, then ask yourself if you really need the
larger compressor, or if you could settle for a little lower duty cycle.
>Oilless or Oiled?
Oilless compressors usually come with direct drive motors and are VERY
NOISEY and less efficient. They are however often a little cheaper than a
belt driven oil-type compressor for the same output capacity.
>I can see myself using air powered ratchets,
Low air consumption, no problem.
>maybe a grinder.
Die small grinders, no problem. BIG die grinders and circular sanders need
lots of air, so will have some limited duty cycle with a smaller air supply.
>Maybe a media blaster
You will want continuous operation for this tool. The only answer is to
limit the air consumption to the available supply. You do this by
selecting the appropriate nozzle.
>and HVLP type paint gun.
No problem. 7 CFM at 40 PSI is typical.
>.... I've got a corner that isn't going to be very useful, but would fit a
>vertical compressor jsut great.
It's amazing how usefull an empty corner can be when you're running out of
space (and aren't we all?). A little shelving works miracles. My 20
gallon belt driven horizontal compressor fits under the work bench, and
it's on wheels (not that it ever gets moved much except for cleaning and
service).
$.02,
Barney Gaylord
1958 MGA with an attitude
http://www.ntsource.com/~barneymg
PS
Yeah, I know I have a two cent piece the size of a wooden nickle.
BG
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