Determining main line duct size, Determining branch line duct size – Grizzly G5954 User Manual

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G5954 5HP Dust Collector

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 in

Figure 19, but using the

inlet size for your dust collector as the main line.

Figure 19. Main line size labeled on sketch.

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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

Figure 20.

Figure 20. Branch line sizes labeled on sketch.

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Here are some frequently asked questions

when determining branch line sizes:

How do I figure which size of branch line to

use if the machine has two dust ports?
Simply add the total CFM given for each size from

Figure 16 and refer to that CFM number in Figure

21. Then, split the branch line just before the dust
ports with matching duct sizes.

What about two machines on the same branch

line?
You have two options:

1. If both machines will be running at the

same time, add the total CFM given for
each size from

Figure 16 and match the

branch line given in

Figure 21.

2. If both the machines will never be run at

the same time, reference the machine
with the biggest dust port to

Figure 21

and add blast gates after the Y-branch to
open/close the line to each machine.

Total CFM

Branch Line Size

600

700

800

1000

1200

1400

1600

Figure 21. Branch line sizing chart by total CFM

(for use when multiple machines share line).