Re: [MV] Air Compressor Recommendation?

From: David Cole (DavidCole@tk7.net)
Date: Tue Oct 14 2003 - 20:56:54 PDT


I'm partial to Quincy cast iron compressors or similar. The run slow and
produce more air CFM per hp that most other compressors. Also, they are
made to run continously (at least the heavier models are) and then can run
that way all day and not overheat.

Warning: A real 5 hp motor draws about 22-24 amps at 230 volts single
phase. Sears and several others lie about their hp ratings. I don't know
how they can do that but they do. To make 5 hp, you need about 24 amps at
230 volts, there is no magic way to get around that fact. It takes about
1000 va (volts times amps) of input power to produce 1 hp of shaft power
for small electric motors.

I have a real 5 hp air compressor with an old Westinghouse Cast iron two
stage head. It works fine for running air tools and sprayers. However
when it comes to blasting, even a real 5 hp compressor comes up short. I
have a 10 HP 3 phase air compressor that I run off a homemade rotary phase
converter to produce air for blasting. It has a large Quincy 2 Stage cast
iron heat that must weigh 150-200 lbs by itself. The pump is rated at 36
cfm. Everything is mounted on a 120 gallon tank. I bought the compressor
complete (less magnetic starter and controls) for $250. The guy just
wanted to get rid of it. I hauled it home and in just a couple of hours I
had it running. A couple of years ago, I bought a second Quincy Compressor
but with a single stage head that is rated at 34 CFM with no motor and a
120 gallon tank for $100. I have a Linsay 200 lb pressure pot that works
well. Lindsay went out of business about two years ago, so parts are a bit
hard to find, but it's a good pot.

The 10 hp Quincy compressor can run a new 3/16 nozzle at 90 PSI not quite
continously. I can blast for about 10 minutes and then rest for 2 and that
works fine. The rest period allows the compressor to catch up and refill
the 120 gallon tank. I end up moving stuff around every 10-15 minutes
anyway it seems so not being able to blast continously is really not a
problem.

The guy on that site mentioned using Silica sand. I think that is a waste
of time and money. Black Beauty or the equivalent furnace slag blasting
media is a lot faster than silica sand and it is much, much safer. (Read -
more metal blasted for less $) IMO, that guy on the web site used the wrong
equipment. Spending 5 weeks of 10 hours days blasting two vehicles! My
blaster chews through about 200 lbs of sand in about 30-40 minutes. But
you can cover a lot of metal in 30 minutes.

My recommendation is to skip Sears all together. Look up sandblasting
equipment in the yellow pages. Visit a commercial supplier of sand blast
equipment and see what they have. Perhaps they have some used stuff they
want to get rid of? Look for auctions, plant closings (they are happening
all over the midwest!), and pickup a nice two stage compressor that can put
out the air. You can run a 1/8 nozzle off a real 5 hp compressor, but you
need to take breaks to allow it to catch up.

If I had to blast a duece and I had no equipment, I'd probably rent a gas
or diesel compressor and a sand pot and buy about 1000 lbs of sand and go
to it. That equipment can easily get the job done in a day. If you buy a
Sears 5 hp compressor (really about 3 hp) and a cheap siphon blaster, you
could spend a week or more blasting the same truck.

Dave

On Tue, 14 Oct 2003 16:10:30 -0700, Paul A. Thomas
<bluewhale@jaxkneppers.com> wrote:

> This list is great! I have received the opinions of perhaps two dozen
> listers regarding their thoughts and experiences with different types of
> abrasive blasting and the manufacturers of the equipment. Based on what
> I can do now and those suggestions, I'm going to buy a Skat 960 cabinet
> soon.
>
> However my 9 month old portable air compressor is not up to the job, not
> even with a small carbide tip on the gun. When I have no other idea what
> to do I usually go to Sears and see what they have, then buy what I need
> ( hopefully ). Could anyone give me their thoughts on brand and type of
> air compressor to look at for this? I found a number of opinions about
> blasting and air compressors on line, but found this one echoed what
> listers were saying closely so thought to TRY to use his
> recommendations..
>
> http://www.speedprint.com/Deves50/Sandblasting.html
>
> However I'm not going to be doing anywhere near the volume he does, so am
> currently considering a Sears unit with an 80 Gal tank, a 7 horse two
> stage engine, 240 volt. Puts out 16-18 CFM at 100-175 PSI. Overkill
> perhaps for the blasting cabinet, but I also will be using a pressurized
> gun on parts of the trucks which will not fit into the cabinet, so the
> extra power will probably come in handy.
>
> Thanks for all of the responses. I don't like spending money, but when I
> have to do it I really dislike wasting it on something that doesn't work
> well. :}
>
>
> Paul
> MVPA# 24986
> '53 REO M35 Fire Conversion
> '53 AEC Chevy 3/4 Ton
> www.paulathomas.com/images
>
>
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-- 
Dave


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