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.

For the Model G0508 this is 9". Mark your drawing as in Figure 26.

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Figure 26. 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 Figure 27.

G0508 10 HP Industrial Dust Collector

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Figure 27. Branch line sizes labeled on sketch.

A few frequently asked questions when deter- mining branch line sizes:

What size of branch line do I use if the machine has two dust ports?

Simply add the total CFM given for each size from Figure 23 and refer to that CFM number in Figure 28. Then, split the branch line just before the dust ports with matching duct sizes.

How do I manage 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 23 and match the branch line given in Figure 28.

2.If both the machines will never be run at the same time, reference the machine with big- gest dust port in Figure 28 and add blast gates after the Y-branch to open/close the line to each machine.

Total CFM	Branch Line Size
600	5"
700	5"
800	6"
1000	6"
1200	7"
1400	8"
1600	8"

Figure 28. Branch line sizing chart by total CFM (for use when multiple machines share line).

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