4" vs 6" duct a big compromise in DC?

[wayne ateser]

Would a small shop DC system run ok with the mains at 4" smooth bore PVC ducting vs 6"? I would have about 30' of main and 4 drops using a 2hp 1600cfm unit and air blocks for the station not used. The DC has a 5" intake and 12" impeller.

I cannot find locally PVC 6" sewer and drain pipe. I can find galvanized 6" duct at about $1.40/ft and 4" smooth bore S&D PVC pipe at $0.58/ft. I hate to spend more of the duct then the DC which would happen if I go the metal pipe route.

I visited all local Home supply brands (HD, Lowes, CW) and all dont carry over 4" pVC. And I called an irrigation supply and they dont carry the light duty 6" PVC pipe (i think its schedule 2379 or something like that). Im guessing that its not a big seller inmy area for some reason to do with building codes for such things.

So any way, I was wondering how much performance I lose by going the 4" vs 6" route.

Any thoughts appreciated!

[CPeter James]

Look at it like this, the area of a 4" pipe vs a 6" is 12.56 sq in vs 28.26 sq in, so for the same velocity of the air movement the 6" is moving twice the air. I know that all things are not equal and that the 6" won't move twice as much air with that 2hp DC, but I hope you can see that those two inches in diameter make a big difference. DC is about moving volumes of air, not about creating vacuums. A DC moves lots of air and the debris with it. A vacuum cleaners moves less air, but has a greater lifting ability.

CPeter

[Chris Singletary]

Try looking for 6" pipe at an a/c supply house. I work at one and can sell you the 6" pipe for $4.35 for a 5' piece. You need to check the a/c warehouses they will kill HD and Lowes on price.

[wayne ateser]

Try looking for 6" pipe at an a/c supply house. I work at one and can sell you the 6" pipe for $4.35 for a 5' piece. You need to check the a/c warehouses they will kill HD and Lowes on price.

OK. The Lowes 6" galvanized pipe that you squeeze together until it locks in shape was $7 for 5' section so thats a big improvement. I like the idea of PVC as it would be more flexible and longer runs so less mounting. I could even make my own fittings to a degree. But if not available then I can do the metal pipe route. Ill call around a bit more to both plumbing and HVAC outfits and see what they got.
thanks

[Jeffrey Schronce]

What would one consider the minimum gauge for this HVAC duct work?

[wayne ateser]

Look at it like this, the area of a 4" pipe vs a 6" is 12.56 sq in vs 28.26 sq in, so for the same velocity of the air movement the 6" is moving twice the air. I know that all things are not equal and that the 6" won't move twice as much air with that 2hp DC, but I hope you can see that those two inches in diameter make a big difference. DC is about moving volumes of air, not about creating vacuums. A DC moves lots of air and the debris with it. A vacuum cleaners moves less air, but has a greater lifting ability.

CPeter
yea. I see. Its a area=PiR2 thing. So as diameter increased the area goes up nonlinearly. Ok. well I just need to make some calls around and see what I can find. Going the metail route is fine too as Chris points out its starts to get reasonablly priced if you find the right place.

[wayne ateser]

Look at it like this, the area of a 4" pipe vs a 6" is 12.56 sq in vs 28.26 sq in, so for the same velocity of the air movement the 6" is moving twice the air. I know that all things are not equal and that the 6" won't move twice as much air with that 2hp DC, but I hope you can see that those two inches in diameter make a big difference. DC is about moving volumes of air, not about creating vacuums. A DC moves lots of air and the debris with it. A vacuum cleaners moves less air, but has a greater lifting ability.

CPeter
Cant the pipe be too big? As on the extreme the DC open ina room wont work. Is there a way to figure out the optimum size. I suppose one way is to get some 6" and test how it does. I dont think they may 5" pipe as thats the opening on the DC. I could open that up I suppose and just mount a sealed fitting over the now widened intake.

[Chris Friesen]

Sure, the pipe can be too big. You need to balance the volume of air you need to move with the required air speed in the pipe.

Generally you want about 4000 feet/minute of airspeed to keep the dust suspended. Ideally you would want at least 800 CFM of airflow to get the fine dust from the worst tools. This usually works out to 6" drops and ducts for a home user where only one tool will be in use at a time. (Although the drops may be further split, say for above/below collection on a tablesaw.)

For a large shop with multiple drops open at once, you still want 6" drops but the main duct may be larger (and of course the collector has to be bigger).

[wayne ateser]

I tried 14 different plumbing, irrigatio, pipe wholesalers for pipe in my area. Not one carries the 6" PVC S&D 2379 (thin wall inexpensive pipe). SOme said they could order it. Most had 6" SDR-35 which is about $2.50/ft.

So my options are down to using the metal ventilation 6" pipe ($1.40ft at Lowes) but I hear the adapters are very expensive....or.......

Keep all ducting at 4" PVC thin walled ($0.58 at Lowes).

[Jim O'Dell]

Wayne, one thing that might help is to let us know where you live. People in the area that know a specific spot for you to try, may not suggest it with the chances being higher that you don't live any where near it. If you live in one of the states bordering Texas I can point you toward a plumbing house that has a presence in each of those states that has tthe PVC 6" pipe in the thin wall. Maybe others could do the same if you live somewhere that is near them.
I don't have the answer to this, maybe someone will, but I wonder if a unit made for 5" is going to work with 6" pipe, or if the air speed drop will cause problems? What about using 5" snaplock of the proper guage, and do 5" and or 4" drops, depending on the tool? im.

[wayne ateser]

Im in Orange County, Ca. If anyone has any ideas where this stuff is stocked that would be wonderful. I tried the 14 places in and around Anaheim.
As far in intake, I read on one fo the dust collection sites thats itss still better to go 6" with just the transition at the impeller. Alternatively, it should be easy to modify the DC case to accept 6" direct.
thanks again

[Wilbur Pan]

Would a small shop DC system run ok with the mains at 4" smooth bore PVC ducting vs 6"? I would have about 30' of main and 4 drops using a 2hp 1600cfm unit and air blocks for the station not used. The DC has a 5" intake and 12" impeller.
The key may be in your first sentence. How small is your small shop?

The reason I ask is that there are two ways of overcoming duct resistance in a DC system.

The first, as has already been discussed, is to increase the diameter of the pipe.

The second is to shorten the run, and the best way to do that is to move the dust collector to each machine as you use it and hook it up with a short length of flex pipe. According to Bill Pentz' static pressure calculator on his website, 10' of 4" flex pipe gives you 2.1" of static pressure, and you can probably get by with much less if you make your dust collector mobile. If that's the only pipe in your system, that's a very low amount of static pressure for a dust collector to overcome.

Now, for a big Norm Abrams-sized shop, this isn't going to be feasible, but then again, you'll have no problem running large diameter duct to a large dust collector/cyclone system.

[Ed Gibbons]

Believe, the bigger the duct, the move air that can be moved. That equals better dust collection.

[Al Killian]

Go with spiral pipe from your local heating suppleir. It is heavier gauge than stove pipe and the elbow and fitting are smother and longer raduis. Get the fitting from any place that sells cyclones, like penn state. I have no connection to them just a happy costumer.