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Determining Main Line Duct Size
The general rule of thumb for a main line duct is
that the velocity of the airflow must not fall below
3500 FPM.
For small/medium sized shops, using the inlet size
of the dust collector as the main line duct size
will usually keep the air velocity above 3500 FPM
and, depending on your system, will allow you to
keep multiple branches open at one time.
Mark your drawing, as shown in the figure below,
but using the inlet size for your dust collector as
the main line.
Jointer
Planer/
Moulder
395
Miter
5"
6"
Saw
98
Shaper
Table Saw
Figure 66. Main line size labeled on sketch.
Determining Branch Line Duct Size
The general rule of thumb for a branch line duct is
that the velocity of the airflow must not fall below
4000 FPM.
For small/medium sized shops, using the dust
port size from the machine as the branch line duct
size will achieve the correct velocity in most appli-
cations. However, if the dust port on the machine
is smaller than 4", make the branch line 4" and
neck the line down right before the dust port.
Note: Systems with powerful dust collectors work
better if multiple blast gates are left open. This
also allows you to run two machines at once.
Experiment with different combinations of blast
gates open/closed to find the best results for your
system.
Write your determined branch line sizes on your
drawing, as shown in the following figure.
Model G0637/G0638 (Mfd. Since 04/12)
Sander
395
790
7"
Dust
Collector
Planer
Jointer
Planer/
395
Moulder
4"
5"
Miter
4"
Saw
98
4"
220
Shaper
Table Saw
Figure 67. Branch line duct sizes labeled.
If two machines will connect to the same branch
line and both will operate at the same time, then
add the required CFM for each machine together
and find the closest total CFM in the table below
to determine the correct branch size.
If both machines will never run at the same time,
reference the machine with the biggest dust port
in the table below and add blast gates after the
Y-branch to open/close the line to each machine.
Total CFM
400
500
600
700
800
900
1000
Figure 68. Sizing chart for multiple machines on
the same branch line.
Sander
790
395
4"
6"
6"
7"
Dust
Collector
4"
5"
395
614
Planer
Branch Line Size
4"
4"
5"
5"
6"
6"
6"
-39-
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