Plastic pipe (or PVC pipe) is unsuitable for dust collection for three reasons:
First, plastic pipe fittings are not offered
in the diversity required to meet design
requirements.
Second, plastic pipe elbows have a
short radius, which encourages clogs and
compromises system efficiency.
Third, and most important, plastic pipe
is non-conductive and builds up a static
charge as charged particles pass through
it.
This static charge can discharge at any
time causing shock and surprise, which
is dangerous around running machinery.
More serious is the risk of explosion and
fire. Fine dust particles suspended in air
have significant explosion potential—all
that is needed is a spark, which the static
charge on plastic pipe conveniently supplies.
Grounding plastic pipe requires wrapping it
in wire both inside and out—an expensive
(and never certain) proposition that negates
the minimal price savings in going to plastic
in the first place.
has none of these disadvantages. An incredible variety of fittings are available and custom fittings can be easily fabricated. The fittings are designed with long radius to minimize clogging, and special fittings such as clean-outs and quick disconnects are available. Most important, Spiral metal pipe is conductive, and simple and easy to ground, even when flexible rubber hose is used to connect the duct to the machine.