-24-
For Machines Mfd. Since 10/20
South Bend Tools
Model SB1100 & SB1101
S Y S T E M D E S I G N
Metal Duct
Flexible Duct
Figure 34. Examples of smooth metal duct and
components.
Advantages of smooth metal duct are its
conductivity, efficiency, and that it does not
contribute to static electrical charge build-up.
However, static charges are still produced when
dust particles strike other dust particles as they
move through the duct. Since metal duct is a
conductor, it can be grounded quite easily to
dissipate any static electrical charges.
There are a number of options when it comes
to metal duct, but metal duct that is specially
manufactured for dust collection is the best
choice. When selecting your metal duct, choose
high quality metal duct with smooth welded
internal seams that will minimize airflow
resistance. This type of duct usually connects to
other ducts or elbows with a simple, self-sealing
clamp, is very quick and easy to assemble, and
can be readily dismantled and re-installed in
a different configuration. This is especially
important if you ever need to change things
around in your shop or add more tools.
Avoid inferior metal duct that requires you to
cut it to length and snap it together. This type
of duct is time consuming to install because it
requires you to seal all the seams with silicone
and screw the components on the ends with
sheet metal screws. Another disadvantage is
the rough internal seams and crimped ends that
unavoidably increase static pressure loss.
Flexible hose is generally used for short runs,
small shops and at rigid duct-to-tool connections.
There are many different types of flex hose on
the market today. These are manufactured from
materials such as polyethylene, PVC, cloth hose
dipped in rubber and even metal, including steel
and aluminum.
The superior choice here is metal flex hose that
is designed to be flexible, yet be as smooth as
possible inside to reduce static pressure loss.
Figure 35. Example of flexible metal duct.
There are also many kinds of pure plastic flexible
hose, such as non-perforated drainage type
hose and dryer vent hose. Drainage type hose,
while being economical, does not quite have
the flexibility required for dust collection. The
inside of the duct is also deeply corrugated and
can increase the static pressure loss by as much
as 50% over smooth wall duct. Dryer vent hose,
while being completely flexible, is non-resistant
to abrasion and has a tendency to collapse
in a negative pressure system. We DO NOT
recommend using dryer vent hose in your dust
collection system.
If using flex-hose, you should choose one of the
many types that are designed specifically for the
movement of solid particles, i.e. dust, grains,
and plastics. However, the cost of specifically
designed flexible duct can vary greatly.
Grizzly.com offers polyethylene hose, which
is well suited for the removal of particulate
matter, especially sawdust, since it is durable
and completely flexible. Polyethylene is also very
economical and available in a wide variety of
diameters and lengths for most applications.
