Run 6-inch pipe from DC with 4-inch drops?

[Marc Rochkind]

I have a Jet DC that I'd like to put in a corner of my small shop, and I can easily find many sources for 4-inch fittings to connect it to my tools (fittings, blast gates, hose, etc.).

However, what I'd really like to do is run 6-inch pipe from the DC along the ceiling, in a single line, with T (or equivalent) connections to 4-inch flexible hose drops.

The 6-inch pipe itself isn't a problem, as I can find what I need in PVC from Home Depot. However, I can't locate any source of parts so I can attach the 4-inch drops. I'm not talking about a 6-inch-to-4-inch fitting, which I can find, but something that would allow a 4-inch drop while continuing the pipe at 6-inches to the next drop.

Keeping the pipe at 6-inches as long as possible is frequently recommended, but I can't seem to find a way to do it. As I mentioned, doing the whole thing at 4-inches is straightforward, but sub-optimal.

Advice?

[Anthony Whitesell]

Are you looking a a 6" by 6" by 4" T fitting? I know the Lowe's here had them. Can you find a 6"x6"x6" fitting?

Unfortunately, my advice is not to make the same mistake I did. Don't use 4" drops. With the exception of hand tools, they can't move enough CFM.

[William C Rogers]

I was initally going to run 4" drops from a 6" main, but have since changed my mind. I am now going to run 6" drops. My table saw is somewhat stationary and it has 4" for the saw and 4" for the Excallibur overarm guard. I will run 6", use a 6" wye to split then reduce to 4" for connection. I believe I can use the sheet metal 6X4 reducers and some flex. Several stationary machines can use the 6" without reduction. I have three machines that are mobile and pull out when needed. MiniMax FS35, Supermax sander, and Dewalt 735. The Minimax can use the 6", but the others are 4". I plan on one drop of 6" adding some 6" flex hose. Then adapting for 4" when using the other machines. I believe again I can use the sheet metal adapter. This way if I get another machine I already have a 6" drop.

From your post if I understand to do what you would want to do is install a 6" wye, then reduce one to 4" with a fitting. But why not run the 6" drop and reduce it at the machine.

[John Donhowe]

Before going ahead with the 6" drops, make sure that your DC can provide enough airflow to provide enough airspeed in 6". According to the venerable Mr. Pentz, you need at least 3800 fpm airspeed for a vertical drop to collect sawdust, and 4500 fpm to collect larger chips (jointer, planer, etc.). Horizontal runs need only 2800 fpm.

Fpm=cfm/area, so if my math is correct, you need 745 cfm for a table saw and 882 cfm for a planer to support 6" drops.

[William C Rogers]

My DC is a Jet 1900. Air flow at 8" is 1900 CFM and velocity at 8" is 5629 rpm. I will be lifting about 10', but think I am ok.

[Marc Rochkind]

Thanks, everyone! I did find the right 6x4x6 part at Lowe's, so I'm OK there. I don't think I really need 6 inch drops, because all the tools take 4 inch and, because of the low ceiling, the drop will be only about 6 feet. Right now, it's all 4 inch flex hose all over the floor, which is a mess, but dust collection is fine. I should be able to clear the floor and also get DC that's at least as good.

[Jim Andrew]

A 4" pipe has the capacity of 1/2 the air of a 6" pipe. So to make your system work, you will have to have 2 gates open. Some machines benefit from having a 6" connection, even if the company put a 4" opening on it. Other machines are designed well for a 4" opening, such as the 15" planer. I was really amazed to find that the Grizzly planer I bought worked so well with a 4" opening, that I did not bother to change it. My edge sander really needed a 6" opening , as with the 4", it sprayed dust all over.

[Chris Damm]

I have that same DC and ran 6" to all my machines and reduced at the machines. I stepped 6" to a 5" blast gate and then to the machine. It works very well. You need to run wyes at the drops not tees. Think smooth airflow back to the DC. Flex pipe if it is corrugated is a airflow killer so bigger is better.

[Ole Anderson]

Marc, have you left yourself open to using steel duct rather than PVC? I wouldn't choke a 3 hp machine with a 6" main, as I have noted many times 7" is the sweet spot for the 650 cfm many machines need. Smaller and you start piling up friction losses, larger and you start dropping chips in the duct. You will never get 1900 cfm through a 6" duct, even an 8" duct would be pushing it. With my 2 hp cyclone I went with a 7" main with 5" hard drops to 4" blast gates and flex for my 4" machines. You cannot do that with PVC as you only find even inch sizes at 4" and above. As stated you don't want to use tees, you need wyes.

[Alan Schaffter]

Contrary to what was stated somewhere above- a 4" duct will pull LESS THAN 1/2 the CFM of a 6" duct- do the math.

OP doesn't say, but what PVC is he planning to use- Sched 40 standard DWV pipe (thick walled, heavy, expensive) or ASTM 2729 ("Solid Perf," etc.) thin walled gravity drain (different OD than Sched 40).

It is harder to find, but ASTM 2729 is what you want to use. 6" ASTM 2729 fittings can be found at Lowes, but not the pipe which is typically only available at irrigation suppliers. Some Lowes may carry SDR-35 (usually green) which has thicker wall and heavier, but same OD as ASTM 2729.

[Mike Heidrick]

Use the least amount of flex as you can and use a 45 off the wye - do not use tees.

[Michael W. Clark]

Contrary to what was stated somewhere above- a 4" duct will pull LESS THAN 1/2 the CFM of a 6" duct- do the math.

Are you requiring the 4" and 6" ducts to run at the same velocity? Two 4" into a 6" is very common.

[Alan Schaffter]

Not a huge difference, but first comparing cross-sectional area-

2 @ 4" A = 12.57 sq. in. X 2 = 25.13 sq. in.

1 @ 6" A = 28.27 sq. in.

Now circumference (friction)-

2 @ 4" C = 12.57 in. X 2 = 25.13 in.

1 @ 6" C = 18.85 in.

Two 4" ducts will have smaller cross-section and larger circumference (more surface area- higher SP) than one 6" duct. For a given blower, higher SP = lower CFM.

[Michael W. Clark]

All true, but system flow is dependent on a lot more than the duct cross-sectional geometry.

You will likely have more flow through a 6" that is being fed by two 4" ducts rather than a single 4". Look at the losses for 800 CFM in a 4" versus 400 CFM. The losses will be approximately 4x at the higher flow, moving you way up the fan curve.