# Choking my dc?



## Mark Pallen (Nov 19, 2017)

I have a general international 10-810 dc. It has the option of four 4" ports or one 8" port. Rated 2800 cfm with 12" water.
My question is..... how much 8 inch pipe should I have before I drop to 6 inch.
Currently I come off the 8" stub with a reducer to 6". Then it branches off at 4 " and 5" drops. Everything works fine but I want to drop a 5" pipe to a panel saw on the floor below . I know my system could be more efficient so I hope to pick some brains for suggestions and ideas. 
Currently piped in on the upper floor is a complete pro woodworking shop each machine with a gate. It is where the dc is but more work is done on the mainfloor .
Moving the dc isnt an option due to height required, near 10 feet.


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## J_L (Apr 22, 2014)

Keep the 8" pipe run as long as possible and keep the 4"-5" runs as short as possible. Immediately coming off the 8 to a 6" will for sure choke the system. Without knowing your layout, is it possible for you to have a main 8" trunk and then Y to a pair of 6" runs for feeding different areas of the shop and then reduce to 4 or 5s at each machine? Also, do you use gates at each machine? If so, you may find that leaving a few open near the ends of the runs will help with dust collection.


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## Mark Pallen (Nov 19, 2017)

Thanks for your input. Looks like I'll be doing some modifications.


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## Carl10 (Feb 3, 2017)

Mark,

I have attached a chart from the American Woodworker magazine that Oneida has on their site. In the article you can see the true performance of your machine (solid purple line). You will see that it had a maximum tested CFM of ~1500. I show this because as you change your design keep in mind the velocity needed for 8" ducting. To keep material airborne you want 3500 FPM which is 1200 CFM in an 8" main duct. What you don't mention is if you ever have 2 gates open at a time. If so then you need to balance the system. If not then I would look at the longest run or highest SP loss of your ducting. So a further straight run may not have as large of a SP loss as a shorter run with more bends and a long flex hose. Use something like this site (there are many ) to determine SP loss https://airhand.com/designing/ Once you know your SP loss of your system you can get an idea of airflow by adding that from the highest CFM SP which looks like ~1"SP @1500CFM. So if you calculate 5" of SP loss due to ducting then you would look at 6" SP and see you would have ~1000CFM (or <1200 CFM needed for an 8" main).

So before you change your ducts look where you are now and compare that to what you plan on doing and you may find a 7" main would make the most sense for your particular setup. 

Hope this helps. Let us know what you do.

Carl

https://www.oneida-air.com/pdf/aww article jan 2006.pdf


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## Mark Pallen (Nov 19, 2017)

Thanks Carl. I'll check this out and update with my result. I initially was in too big of a hurry to research and design the system properly and now I'm forced to look at the numbers and do it more efficiently. 
Its a one man shop so only one gate is ever open at a time.


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