Hello Mark,
Depending on the dust producing machine's suction needs, you can either use a 6" trunk line and branch into 4" drops for each machine. If you have two (2) 4" branch lines splitting from a 6" pipe, there would be higher CFM over having a single 4" in most cases due to the pipe diameter being a factor that affects the overall CFM that can be pulled but you could also run from 6" to a single 4" if you need more velocity rather than CFM too.
Having as few 90-degree elbows and minimal flex hose helps to reduce friction and resistance in the system. The dust processor's static pressure needs to be able to overcome this friction and resistance in order to be able to pull material through the ducting and by eliminating as many sources of unneccessary pressure loss as possible will make the system perform optimally. Flex hose can be a convenient option for very short runs, but if using a lot of it, there will be more resistance that the machine will be trying to overcome to perform and it may negatively impact the airflow and velocity depending on the configuration. Sealing joint with a tape is typically only needed for PVC pipe, but a better option would be going with clamp-fit ducting as it is much less cumbersome to work with if the system needs adjusting or inspected for a clog etc.
Nordfab and Carolina Air Systems are good options for ducting, I highly recommend contacting one or both of them for duct design consultation and quotes on clamp-fit ducting as they are both good resources.
Please let us know if you have any questions or need further assistance.
Thank you and have a great day!
Mark Peasley
I'm new to dust collection. I've read alot of varying opinions/do's/don'ts on the internet as to how one should go about setting up the ducts in a shop. I'd like to hear from the experts here as well. Here're my assumptions of how I should build the duct system:
Main lines are done with 6" DWV PVC pipe since that's what's coming out of the D700. Each time you branch to go to a tool(s), you should split to (2) 4" DWV PVC pipes to maintain the airflow volume. Blast gates are used to seal off all the lines except the line to the tool(s) you need. You should not take a 6" down to a single 4" pipe but instead go to 2 lines that are open otherwise you reduce your airflow & tax the system. Never use a 90 degree corner, go with (2) 45 degree corners to make a 90. Seal joints with metal duct tape. Limit the use of flex hose as it slows airflow substantially. I'm not sure how 2" flex hoses to potential hand tools might be handled - I need to research it more.
Sound about right?
Thanks,
MP