Vertical duct size

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Whiskey Bob

New member
Hey, my first post. I am laying out the ducts in my shop and will have a main 6" PVC line running along the ceiling on two sides of the shop. At various points will be PVC drops to a blast gate at each tool. Most of the tools will be connected with 4" flex hose from the blast gate to the tool port. Should the vertical runs be 4" or 6"? I've seen photos with 6" drops that reduce to 4" near the tool, and also 6" mainline with a reducing wye that goes to 4" down to the tool. Any advice is greatly appreciated.
 
Bob,

Your best performance will be to maintain 6" duct all the way and also consider making new machine ports that are 6" rather than 4" and use both 6" blast gates and 6" flex hose for the final connection (I have made 6" ports for my jointer and tablesaw using plywood with 1/2 of a PVC straight coupler glued into a clearance hole cut with a jigsaw). There is very significant airflow loss through 4" versus 6" (12.5 square inch area cross section in 4" versus 28 1/4 sq in in 6"). Also minimize the amount of flexible duct you use as it also has high resistance to airflow (1 foot if flex = 10 feet of straight pipe). I also recommend using the lightweight Sewer & Drain pipe for your duct (it is white ASTM D-2729 bell end PVC found at plumbing or irrigation supply houses; you can get fittings at many big box stores in the Sewer & drain aisles). Use 6" x 6" x 6" wyes for drops from your main and 45 degree elbows to make the remaining turn for straight down to your machine. Never use 90's as two 45's connected with a short straight section offer less airflow loss. If you do need 4" on smaller machines, get the ClearVue 6" to dual 4" transitions -- I also recommend their blast gates for use with PVC.

Hope this helps.
 
OK, thank you. Sounds like the sensible way to go. I keep reading that the D2729 pipe and fittings are available all over. I can find the 4" diameter, but 6" is very, very hard to find, and the fittings are four times the cost of 4" fittings. I can find fittings on-line and shipping shouldn't be too bad, but I wouldn't dare to guess the cost of shipping 10' sticks of straight pipe. I'll keep looking and asking around.
 
I'm not sure what part of the country you are in, but folks have found 6" D2729 pipe at major plumbing supply houses or irrigation or farm supply companies. Many Lowes and Menards store carry 6" fittings in their drainage aisle in their plumbing departments. I know that McMaster Carr also carries fittings and I recommend their economical 6" PVC flexible duct (1/2 the price that ClearVue has, which I believe they get from Wynn Environmental).
 
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