Grant Erwin wrote:
The cleandryair page claims that the ONLY meaning of CFM is as the
input volume of an air compressor. Thus to them 16 cfm @ 90 psi would
have no meaning. As this is in direct conflict with the way many if
not all industrial air compressors are specified (if you don't
believe me just google on: compressor cfm psi
and see all the bazillions of specs in this format, it only takes a
second)

I find their attempt to limit this terminology to be unhelpful. That
page does little to shed light and in my opinion is designed to steer
people to their way of thinking and thus their product line whatever
that is.

There *are* valid thermodynamic concerns here, but they aren't
relevant to my original question. It is true that it is inefficient
to compress air to a high pressure (with lots of heat) and then
remove the heat and moisture to get clean dry air. Obviously you are
spending electrical $$$ to dump heat into some heat exchanger. This
is a fact. What I would find a more helpful fact is the information
how to get clean dry air without doing the above. I have always
understood that the way to go is to get a 2-stage compressor which
can run a high volume of air at a high pressure (like 180 psi, gaged,
or 180 psig) and then pipe that air to a refrigerated air dryer and
then filter the moisture and oil drops out of the air. I think
Richard Kinch's point is that you will get a lot more energy out of
that same compressor if you use it hot and wet. Very true, but you
can't spray-paint a car with hot wet air, nor can you run it into a
plasma cutter, nor is all that moisture good for your air tools.

The best bet with an HVLP gun is to use a turbine or regenerative blower
like the ones Spencer makes (vortex blowers) The moisture is generally not a
problem under reasonable humidity conditions. I have an Accuspray gun and
run it both ways. Using a compressor it will keep a 5 HP 3 phase compressor
running more than 50% of the time and you end up with a lot of moisture to
handle.





Way back when I first posted the question, I was wondering about
using a "regular" air compressor to generate air for HVLP painting.
As I knew for sure you couldn't get the kind of volume out of my
compressor that a HVLP gun needs, I wondered if you could "transform"
it to a much lower pressure but much higher volume. I now believe
enough light has been shed on that issue to say yes you can get
higher volume by regulating to a lower pressure as long as the
temperature doesn't drop.


I think Ned Simmons is on the right track in this thread. Yes, you can get a
higher volume of air at lower pressure but it is not efficient to do so with
a regulator. Compressing air just to decompress it without recovering any
energy is extremely wasteful. Applications using compressed air that need to
move large volumes of air use the venturi principle, not regulators. Do you
see how the transformer analogy does not apply?