F. Parker on sun 21 may 06
This side of, say, snake oil, air compressors have to be among the most
shamelessly misrepresented products out there. Getting the right one
depends on the details of how you plan to use it -- and by "details" I
mean the specific demands of each of the uses you plan. Of those
mentioned, the spray gun is probably the most demanding on a compressor,
but you should check the specs on the other items also, and be sure you
get adequate capacity. What does this mean? Many will already know the
answers but you might not, so read on...
For the vast majority of A/C buyers, if a pneumatic tool -- say a spray
gun -- lists "40 psi" as its air requirement, then they go out in search
of a compressor that can deliver 40 psi. If this is all they look for
they risk making a HUGE mistake. Practically any compressor can deliver
40 psi air pressure. What is missing is actual "air delivery
requirements" or VOLUME of air needed at 40 psi. This determines
compressor size and often it also determines type.
A conventional airspray paint gun can require upwards of ten cfm (cubic
feet per minute) of air AT the specified 40 psi. Not all do, so it is
VERY IMPORTANT to check how much volume -- and at what pressure -- your
spray gun needs. Granted, most potters only spray for very short periods
compared to people who paint furniture or cars, but it is still important
to get a sprayer that works for what YOU plan to do with it. For example,
a typical airbrush compressor would not power a paint spray gun.
Other applications you mentioned (extruder, et al) are not so dependent on
large air VOLUMES, but might need high air PRESSURES. Again, check their
specific needs and buy for the highest air PRESSURE and highest air VOLUME
you will need AT THE SPECIFIED PRESSURE. If you plan to run several
applications at the same time (multiple potters working simultaneously)
then you must add all the volume requirements together, plus a safety
factor, to have enough capacity -- again at whatever pressure is called
Now to the "snake oil." Compressor specs are completely meaningless
UNLESS they include air delivery as cfm @ psi. The same compressor can
deliver much greater cfm at low pressures than at high pressures. Getting
15 cfm at 10 psi is easy. Getting 15 cfm at 175 psi takes some real
hardware! Usually, air delivery for compressors is given at two
pressures -- one high, the other relatively low. Sears used to be one of
the worst offenders in misleading buyers by offering compressors that
could deliver "125 psi!" with no mention of the piddly 1 cfm volume it
Generally, compressors sold for home use will be "single stage"
compressors which can usually provide 125 psi. "Single stage" means the
air is compressed once, then sent to the holding tank for use.
Commercial/industrial compressors are often "two stage," which means after
the air is compressed once, it is sent to another internal compressor and
compressed again before being stored. These compressors typically deliver
air at 175 psi, and at much higher volumes. They also cost more -- much
more in some cases.
Size matters -- especially when it is an air compressor's holding tank
size. Bigger tanks generally permit operation of air tools that require
high volumes of air (spray guns for instance) with smaller compressor
pumps -- at least for a short time, after which the tank has to be
repressurized. For most potters, this should be ok, because it doesn't
take long to spray a pot, and during the setup time between pots, the
compressor can repressurize the tank.
All of this is general, and applicable to "conventional" airspray
equipment. High volume, low pressure (HVLP) spray guns operate at lower
air presssures (to minimize overspray losses) with huge volumes of air to
push out the material. Again, check the gun specs if this is what you
plan to use, and match pressure/volume requirements to the compressor.
As far as oilless, oil-lubricated or other compressor technologies are
concerned, I believe the oilless are generally smaller compressors. If it
turns out you need something that can deliver 15 cfm @ 90 psi, it probably
won't be an issue. Oil-lubricated will be the only thing available.
AMong the larger, two stage compressors you have a choice of "splash
lubricated" or "pressure lubricated" pumps. The latter forces oil via an
internal oil pump to lubrication points. The former just splashes it
around the crankshaft. I doubt you'll have to get into that.
Finally, one last consideration I belive is important: whether the
compressor is stationary or portable. If your studio is a "real" potter's
studio where you make a living with clay, then you might want to buy a
larger "stationary" compressor and tank and install it permanently around
back in a sheltered alcove of some kind where you can pipe compressed air
to wherever you want it. It's convenient, quieter and you can limit
compressor maintenance chores (changing oil, etc.) to a place designed for
that without having it all over your studio. If your operation is much
smaller, a roll-around compressor might do. IF YOU PIPE the compressed
air you should NEVER use PVC or plastic pipe. I know -- it is rated for
400 psi or so, but that is WATER PRESSURE, which is constant. Air
pressure in a piped system varies with every stroke of the compressor's
piston(s). In time, it can fatigue and burst, propelling shards of PVC
everywhere, including into one's eyes and body! Don't use PVC. Black
cast iron seems to be the standard.
I'll close with the same tired old admonition that's been going around air
compressor sales for years: "Buy as much as you can afford..." with the
caveat that you don't have to buy MORE than you need -- but be sure to get
at least that much.
On Sat, 20 May 2006 08:50:06 -0700, Linda T Ferzoco
>I've been looking for bargains on eBay. What brands
>are more reliable in your collective experiences?
>Anything else I should keep in mind?
Linda Ferzoco on sun 21 may 06
Thanks! You and Phil have been very generous with
your expertise. Phil, being the lover of an earlier
generation of tools, points out that cast iron tanks
are worth the time and money too.
And I found this guide at an online site:
They also say to buy by CFM.
I've got the message. Now, I have to wait to find one
listed on eBay that's near me. These larger beauties
are typically pickup only. Or spend the bucks for
Thanks guys! Love you and love the internet!
--- "F. Parker" wrote:
> Hi Linda:
> This side of, say, snake oil, air compressors have
> to be among the most
> shamelessly misrepresented products out there.
Snail Scott on sun 21 may 06
At 08:55 AM 5/21/2006 -0400, Tom S wrote:
>...IF YOU PIPE the compressed
>air you should NEVER use PVC or plastic pipe...In time, it can fatigue and
burst, propelling shards of PVC
>everywhere...Don't use PVC...
Pay attention to this! I've seen PVC pressurized
air systems last for years and work fine, and they
sure are easy and cheap to install. But...
I was working in a shop where one finally blew. It
sent shards 100 feet, with enough force to drive them
though the drywall an inch from my head. That was a
big building, and we were all far away from the pipe
when it happened, but any one of us could have been
facing that way and taken a three-inch dagger of PVC
in the eye. Just luck that we were all uninjured,
except for inhaling the clouds of flying fiberglass
insulation torn loose in the rupture.
My own workspace (and yours, too maybe) is a whole
lot smaller, and anything similar happening there
wouldn't miss much.
If you gotta install air lines on the cheap, or in a
minimal or temporary situation, use rubber air hose.
When it gives, you get a leak, not an explosion.
p.s. The cheap air hoses at Harbor Freight are crap.
Pay ten bucks more for the good ones, and they'll
last ten times as long.
pdp1@EARTHLINK.NET on mon 22 may 06
Well, the Tanks themselves ( but for lower
pressure riveted Copper Tanks sometimes, in really
arcane stuff, ) have practically always been made
of Sheet Steel, formed or pressed to assume a
Cylinder of some kind, with dished or rounded ends
of the same material, being added.
At one time,
the Tanks tended to have Riveted seams along their
length and for the end pieces, then,
Welded seams became universal.
Now-a-days, Cast Iron tends to be used by more
conscientous Manufacturers for the Air Pump body,
or, according to the kind of outfit they intend to
be making, anyway,
or, at least for larger or more Industrial or
models where durability is to be offered, and
Alluminum alloy or something looking like it
anyway, tends to be used for the Air Pump bodys
of most smaller, portable, inexpensive, or 'May
Fly' kinds, with
many of these having Teflon or similar short
Pistons, and short alloy Cylinder inserts
internally, entirely different from the kinds of
Pistons and longer strokes and integral Cylinders
used in Cast Iron Pumps.
Now, these can last ten or fifteen years of
frequent use, and be a heck of a good deal bought
new for one's Carpentry Nail Guns being used on
building sites and so on, but, are noisy and some
may be 'lemons'.
Some 'medium' sized and lerger Air Compressors
used to be made, which anticipating long periods
of continual operation, were Water Cooled...and I
think that was a very polite thing to do, too.
I do not know if any such are made to-day...or are
still being made in the 'medium' size range.
Large ones probably still are...
When Air is compressed it generates or releases
Heat, and an Air Compressor's Air Pump bodys and
Cylinder Heads especially, will get 'hot'...and
some, or any when run constantly, will get very
Wet cloths, dripping 'wet', layed on them, with a
five Gallon Can hung above that, full of cool
Water to KEEP trickleing or fast dripping onto it,
with a robust Fan set up next to it to blow
ambient Air over it...is a kind thing to provide,
if working one long and hard.
The old 'LeRoy' I was thinking about getting ( and
might still decide to get) is Water Cooled both
for it's Engine and it's Air Pump, and has a Water
Pump to circulate the coolant through a large
Radiator with a mechanically driven Fan to move
the Air through the Radiator.
For occasions of more sustained use, and or
heavier-draw use, as others have mentioned also of
course, larger capacity 'workshop' size models
having a Cast Iron
Pump, having Oil, wet sump Crankcases, running at
lower rpm, are what is to be recommended.
CFM @ 100 9or @125, 175, 200, 250 ) psi is the
useful index of output...and
may easily be extrapolated to relate to the
particular CFM @
whatever PSI any given Tool or device may prefer
itself to work or run well.
Certainly, something such as Air Cylinders for
Extrusion or push-pull motions, do not use any Air
to speak of, or do not expell it in operating, as
Impact Wrenches, Spray Guns or many other kinds of
Air Tools do...and the Cylinders one wishes to
operate with the Air, just need enough
volume at a given pressure to be available to
them, for them to make their limited
motion...while they do not axhaust the Air or
oblige the Air Compressor to keep provideing it
A nice, well made, Electric Motor driven, low-ish
rpm Compressor, you can stand right next to while
it is running and coming up to pressure, and have
a normal conversation with a friend, about how
nice it is, to have one so pleasant...
----- Original Message -----
From: "Linda Ferzoco"
> Thanks! You and Phil have been very generous
> your expertise. Phil, being the lover of an
> generation of tools, points out that cast iron
> are worth the time and money too.
> And I found this guide at an online site:
> They also say to buy by CFM.
> I've got the message. Now, I have to wait to
> listed on eBay that's near me. These larger
> are typically pickup only. Or spend the bucks
> Thanks guys! Love you and love the internet!
> Linda Ferzoco
> --- "F. Parker" wrote:
> > Hi Linda:
> > This side of, say, snake oil, air compressors
> > to be among the most
> > shamelessly misrepresented products out there.
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