Determining Branch Line Duct Diameter
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 the system.
Write the determined branch line sizes on the drawing, as shown in Figure 51.
395 | 395 | 790 |
|
|
Multiple Dust Ports
If the machine has multiple dust ports, add the total CFM given for each dust port size from Figure 47 on Page 36. Refer to the chart in Figure 52 and find the CFM that is closest to the total to determine the correct branch size. Split the branch line just before the dust ports with match- ing duct sizes.
Total CFM | Branch Line Size |
600 | 5" |
|
|
700 | 5" |
800 | 6" |
1000 | 6" |
1200 | 7" |
1400 | 8" |
1600 | 8" |
Figure 52. Branch line sizing chart by total CFM (for use when multiple machines share line).
Two Machines on Same Branch Line
If both machines will be running at the same time, add the total CFM given for each dust port size
98
4" 4" 6"
from Figure 47 on Page 36.
4" 8" 8"
4" | 4" | 5" |
220 | 395 | 614 |
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