Dust collection hose diameter

[postalgbv]

I have a 1.5 hp dust collector with 4" hose. My cnc router dust boot has a 3" (inside diameter) pipe leading from the boot. I don't have alot of extra head room above the machine and wanted to know if it's any difference to run 3" tube entirely from the dust collector to the dust boot, or to run 4" all the way to the boot then step down at the last moment... Would there be a noticeable performance difference?

The run would be about 25' from collector to boot.

[jemmyell]

Run the 4 inch hose as far as you can. There will be a big difference in airflow if you don't.

-James

[cabnet636]

1.5 at 25' is begging forair as it is.. in dust collection it is about large volumes of cfm's not vacuum as in hold down

http://billpentz.com/woodworking/cyclone/Ducting.cfm

and

http://www.airhand.com/

jim

[postalgbv]

thanks guys. 25' was an estimate, should be quite a bit shorter if I route it efficiently. I'll keep the 4" as long in the chain as I can. Can't upgrade the dust collector or hose size any more due to space constraints right now.

[cabnet636]

eric i will up grade the dc in the near future after i finish installing the new machine, i'll save one of the smaller dc we have now for you i have several 3hp and a 2hp or two

jim

[adriand]

Hi;

If you reduce the diameter from 4" to 3" the air velocity will increase which is a good thing. If you have the cfm capacity of the dc I could calculate the velocity assuming the vendor used 3500 fpm as a baseline for the 4" duct.

You would need to put a 3" to 4" transition between the 3" hose and the beginning of the 4" duct run. Dont remove the existing duct run, you need to slow the air down before it gets to the dc so you dont stall the fan / overload the motor.

So long as the router is the only device connected to the dc, and the hose is 25 feet there should not be too much problem.

Its better to use smooth steel duct than flexible hose, flex hose has too much static loss. Usually flex hose hose is only used for 6 feet or so to connect the tool to the main duct run.

The 4" duct is really only suitable for 1 machine anyway. In most industrial situations, a 6" pickup would be used but it depends on the type of dust being collected and how hazardous it is.

Hope this helps

[Geof]

Originally Posted by adriand Hi; If you reduce the diameter from 4" to 3" the air velocity will increase which is a good thing...

This is halfway correct; the configuration being discussed is 3" diameter at the pickup end increasing to 4" diameter for the main collector duct. This is an increase in diameter for the air flow so there will be a corresponding decrease in the air velocity which is a bad thing. It is likely that heavier dust particels which were picked up by the flow in the small diameter will settle out when the flow diminishes. As someone pointed out with dust collection it is rate of air flow not amount of suction that is important; if the pickup diameter is 3" it may be better to use 3" for the entire run. Failing that install a Y junction with a gate at the location where the increase in diameter occurs so hat periodically the gate can be opened to get a good air flod to flush through any settled-out dust.