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.
Use the inlet size of the dust collector as a starting point for the main line. Neck the main line down 1" for every 10' of length. This 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.
For the Model G0671/G0672/G0673 this is 10". Mark your drawing, as in Figure 33.
(.* 
(.* 
,.%
.-
9“ 10“
''% | (.* | +&) |
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Figure 33. 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 reduce the line 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 34.
(.* 
(.* 
,.%
4“ | 9“ | 10“ |
4“ | 4“ | 5“ |
''% | (.* | +&) |
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Figure 34. Branch line sizes labeled on sketch.
Multiple Dust Ports
If your machine has multiple dust ports, add the total CFM given for each dust port size from Figure 30. Refer to Figure 35 and find the CFM that is closest to your total to determine the cor- rect branch size. Split the branch line just before the dust ports with matching duct sizes.
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 from Figure 30.
If both the machines will never be run at the same time, reference the machine with biggest dust port to Figure 35 and add blast gates after the
Total CFM | Branch Line Size |
<500 | 4" |
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600 | 5" |
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700 | 5" |
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800 | 6" |
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1000 | 6" |
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1200 | 7" |
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1400 | 8" |
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1600 | 8" |
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