Subject: Re: air compressors

From: [email-masked] (Jon Johnson)
Date: 10 May 1995 05:40:00 GMT

ROMEUG ([email-masked]) wrote:
: needing an aircompressor, primarily for sand/bead blasting.  would single
: phase do the job?  perhaps 5-6hp, 9.6 scfm 90lbs?  only be used a couple
: times a week, hour at a time.  appreciate any help.  also, seen quite a
: few from4-500 dollars, devilbiss, campbell-hausfield, etc. any
: recommendations.

Quite a few others have posted replies, comments, etc. here, so I'll add
mine.....

It seems manufacturers can get away with "cheating" on the HP ratings of the
motors because they know people will buy them; that people don't know a
horsepower from a hole in the ground.

The motors on Sears, Sanborn, and other "amateur" models are often less than
HALF the physical size of those on similarly rated "professional" models...

The point is:  the "amateur" models are rated at PEAK DEVELOPED horsepower.  
The "industrial" models are rated at the horsepower they can provide
CONTINUOSLY. The "amateur" models, if rated by CONTINUOUS horsepower, would 
probably be around 1/2 what they claim.

Here's a hint...go to a machine shop.  See what they have.  If it's a 5 HP
compressor, chances are good that the both the compressor and motor are both
physically larger than the motor/compressor unit (as a whole) are on the
Sears, Sanborn, etc.  And it's not because it's old.

Anyone doing a large amount of sandblasting should only consider an
industrial model.  A 5 HP industrial will most definitely outperform a "5
HP" 'amateur' model.  Some names....deVilBiss, Quincy....

Some of the companies make both industrial and amateur.  Expect to pay a lot
more for the industrial models.  It may end up being cheaper in the long
run...the service life will be much better, and you'll be happier.

Hey...isn't that what it's all about?  Hapiness?

--Jon Johnson
[email-masked]

P.S.--5 HP is about the largest practical size for 220V single-phase.

---

From: [email-masked] (gary preckshot)
Date: 12 May 1995 20:26:05 GMT

In article <[email-masked]>, [email-masked] (Jon Johnson)
wrote:
[Stuff about blasting and motor ratings]

The thing to look at is CFM.  So far, Sears and other hobby supply stores
have been relatively honest about CFM.  A two-stage industrial compressor
rated 5 Hp continuous duty is rated about 18 CFM.  Someone in this thread
mentioned 6 Hp and 9.6 CFM.  You see the difference?

Other things:  a robust 5 Hp or larger machine usually has a double 5/8
V-belt drive.  The compressor is iron, no aluminum except the pistons
inside.  The machine is fairly quiet, and runs at relatively low rpm. 
It'll run that way all day.  Check: should weigh about 650 lbs for an 80
gal 5 Hp ASME tank machine.

Big tanks help.  An 80 gallon tank means that for incidental air use, the
machine will pump up every hour to two hours.  An industrial 5 Hp machine
supports continuous sandblasting with small can sand blasters (3/16 nozzle)
with almost no sweat.

ASME-rated tanks are built to American boiler codes.  Over 100 years of
experience there.  Lot of people died to get that experience.

A real industrial 5 Hp machine has a motor starter, a relay operated by the
pressure switch, so the pressure switch isn't burned up by high motor
currents.

A pertinent question: is it worth it?  I thought so.  After two toy
compressors wore themselves and my nerves out (due to noise and
frustration), I went for a big one.  There's something to be said for never
having to wait.  I wouldn't go back.

G.

---

From: [email-masked] (J. Kimberlin)
Date: 10 May 1995 17:16:49 -0700

>P.S.--5 HP is about the largest practical size for 220V single-phase.

I agree and also want to comment that a good used 5 hp 80 gal Quincy, 
deV.B. go for about $500 at machinery dealers.  It is worth getting one 
of these and rebuilding it as needed - most only need cleaning up and an 
oil change.  If they cost more than $500, the dealer has refurbished it, 
but you can sometimes get the ones that need rebuilding for $300 +-.

JerryK

---

From: [email-masked] (Mark Kinsler )
Date: Thu, 11 May 1995 00:26:33 GMT

>The bad part about running the compressor for a long time is the
>compressor, tank, copper tubing piping, and even the sand blaster
>pressure vessel get warm and even hot.  When that happens, even with
>an air dryer of the proper capacity, the pressurized air gets humid,
>wet, even here in Northern California.
>
>The end result is the sand gets moist and all forward motion comes to
>a halt.  Ya can't blast with wet sand!
>
>It is bad enough that I have considered putting fins on the copper
>tubing or running the air through a heat exchanger.  And yes, I have
>the downrisers on the supply headers coming off the top of the header,
>up through a high gooseneck and then down to the air distribution
>manifold.

When I installed the 5 hp air compressor that runs off the engine of The 
Beloved 1964 Econoline Van I used plastic pipe for all the plumbing.  
This worked fine until I started sandblasting, which melted the plastic 
pipe near the compressor outlet enough so that it ballooned into an 
interesting shape before it failed.  I added a long length of copper pipe 
for a heat exchanger.  This wasn't adequate.  So I made up a coil out of 
8 feet of 1/2" copper pipe and stuck it into a 5 gallon plastic bucket 
behind the passenger seat.  Filled up the bucket with water.  Now I can 
sandblast all day and the piping stays cool.  
  Haven't had trouble with moisture in the sand except when I left a bag
of sand on wet ground.  300 degrees for 30 minutes in the kitchen oven
dries it out nicely. 
 The water in the bucket gets good and hot after a while, but it hasn't 
come close to boiling.  When I'm not sandblasting I keep the bucket empty 
and store odd junk in it along with the coil.

                                           M Kinsler

---

From: [email-masked] (Ron Peiffer)
Date: 14 May 1995 17:20:03 GMT

I just purchased a new single stage "6" hp Sanborn/Coleman compressor
on a 60 gallon tank.  The first job for it is sandblasting, sanding and
spray painting approx. 200 ft. of steel fence.  I'm about half way through,
and I would say that this is about the smallest unit that is up to the
job.  If I was going to do a lot of this, I would opt for the 2-stage unit
with the "real" 5 hp motor.  (Both are available at Sam's)  Most of my
work will be much less demanding, and I expect to be quite happy with my
single stage "amateur" compressor -- especially at less than half the
price.  Also, I live at approx. 5000 ft., people at lower altitudes would
probably see better performance.

The "6 hp" motors on the single stage compressor draws 15 amps at 220 
volts while the 5 hp 2-stage unit draws 20 amps.  If you want to compare 
two motors, I would use the voltage and current ratings rather than 
horsepower.  Just make sure the motors are rated for continous use.

Someone, alluded that the 2-stage "industrial" units are quieter.  Is
this true?  Reduced noise might be almost as strong an argument for the
2-stage units as increased performance.