Grizzly G1028Z/G1029Z Determining Main Line Duct Size, Determining Branch Line Duct Size

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 23, but using the inlet size for your dust collector as the main line.

	���	���	���
���		���	���
	���
		���	���

Figure 23. 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 24.

G1028Z/G1029Z Dust Collector

	���	4''	���
4''		5''	6''
	4''
		4''	4''

Figure 24. Branch line sizes labeled on sketch.

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 20 and refer to that CFM number to Figure 25. Then, split the branch line just before the dust ports with matching duct sizes.

What if two machines share 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 20 and match the branch line given in Figure 25.

2.If both the machines will never be run at the same time, reference the machine with biggest dust port to Figure 25 and add blast gates after the Y-branch to open/close the line to each machine.

Total CFM	Branch Line Size
400	4"
500	4"
600	5"
700	5"
800	6"
900	6"
1000	6"

Figure 25. Branch line sizing chart by total CFM (for use when multiple machines share line).

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