results, there were a few web sites of spray paint
equipment manufacturers. One of these was the Sharpe Manufacturing Company
at www.sharpe1.com. Their web site not only contained product information
but also discussion of the plumbing required and a couple of diagrams of
typical installations. I also found a very straightforward discussion paper
titled “Designing a Proper Air Line System for your Shop”. Unfortunately it
is no longer available on the web but I have it on my computer if anyone
would like a copy.
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Figure 2 - Compressor input, drain point, |
There are some simple rules for an installation such as
this. The first one always being safety. Plastic pipe is definitely out. As
one author put it “a great shrapnel source in the event of a rupture and a
wonderful way of force-feeding a fire”.
Of the available types of piping, regular black gas pipe is the most common
and cost effective. Fittings are readily available and, aside from a couple
of pipe wrenches, no special tools are required since most suppliers can cut
to length and thread the ends. We’ll come back to discussing the pipe
installation after looking at a couple of other issues.
I needed to decide where to locate the compressor. Outside was not an option
– our estate doesn't allow garden sheds. We decided to see if it would be
too noisy if it was in the basement. The noise level in the house is just
tolerable and sometimes it is better not to work on the airplane to ensure
household harmony.
Moisture and contaminants in the compressed air are the bane of air tools
and spray paint. With a well
maintained permanent installation it is unlikely that
contaminants can enter the system but moisture will always be present. When
air is compressed it heats up. In hot air, water remains as vapour and is
carried along from the compressor to the air tool or spray gun. Any air
distribution system should therefore provide cooling and drainage to remove
the moisture from the air. Contrary to what the manufacturers may imply, a
water trap will not stop vapour from condensing downstream of the trap.
Traps are designed for liquid water and until the air is cooled sufficiently
(remember the dew point/temperature questions in your FAA written?) the
water remains as vapour. Our best defense against moisture is to cool the
air as it comes out of the compressor. Once the vapour has condensed we will
need a way of removing it from the distribution pipes.
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Figure 3 - Drain point in garage |
Another consideration is the pressure drop between the
compressor and the outlet. The longer the run from the compressor, the
larger the pipe required to provide good flow at high pressures. This is
going to have a cost impact. Larger diameter pipes require larger fittings.
Once you get above about ¾”, items like ball valves jump from under $10 to
up near $20. The recommendations I’ve read advise an optimum size of 1-¼”
and a minimum size of ¾”. For a one-man shop, consuming a three to four CFM
flow, I decided that ¾” would have to be adequate. As it turned out, I don’t
think I would see any difference with a larger diameter pipe.
The system I installed (Figure 1) includes a vertical seven foot section of
2” pipe adjacent to the compressor. This slows the air flow and provides a