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Forum topic by OLCHIEF posted 09-30-2020 08:12 PM 401 views 0 times favorited 12 replies Add to Favorites Watch
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OLCHIEF

44 posts in 264 days


09-30-2020 08:12 PM

I have a 3hp Jet cyclone DC. It is a few months old and a new and bigger dust collector is out of the question right now. I ran about 40 feet of 8” metal duct 12’ above the floor, straight to an elbow and down to the 8” port of the Dust Collector. There are 5, 8” x 4” wyes with flexible duct from the main line to the main machines, blast gates at each machine and tight seals all around. I did some heavy jointing, planning, and routing and ended up with a buildup of chips in the main line which really obstructed airflow that had to be cleared manually. My question is can I avoid future problems by adding a blower at the far end of the main line to increase positive airflow in the system. What do I need to consider?

-- OL CHIEF, Florida Panhandle


12 replies so far

View fivecodys's profile

fivecodys

1660 posts in 2519 days


#1 posted 09-30-2020 08:21 PM

My first thought was that 8” duct might simply be too large for the 3HP blower motor to keep the chips and dust suspended in a run of that length. Have you been to Bill Pentz’s website? The guy is the Yoda of dust collection. You may find an answer there.
I am not sure what the issues are in adding another blower motor. Seems like there was a thread like this a while back. You might try using the search field to see if you can find an answer here.

Please post back with your solution as I am very interested in this topic.

Good luck sir!

-- A bad day woodworking is still better than a good day working.

View ibewjon's profile

ibewjon

2078 posts in 3676 days


#2 posted 09-30-2020 08:48 PM

I think that 8” is oversized. I have a 2 hp with 5” duct. 6” is 50% larger than 5”, and of course, 3hp is 50% larger than 2hp. 5” is about 20 sq. inches. 6” is almost 30 sq inches. 8” is about 50 sq inches. I don’t know the size of impellers, or the cfm, but too large of duct lets the velocity drop, and the chips settle out. Just my thoughts.

View Fred Hargis's profile

Fred Hargis

6502 posts in 3376 days


#3 posted 09-30-2020 09:45 PM


My first thought was that 8” duct might simply be too large for the 3HP blower motor to keep the chips and dust suspended in a run of that length.

Good luck sir!

- fivecodys

There’s likely 2 issues. The 8” duct which may is fed from a 4” line. You only have the air that a 4” duct will allow (not much) going into an 8” duct which really slows down with the increased size. The 8” is almost certainly too large anyway for your unit, you compounded it with the choking down at the wyes. One thing you might try is keeping one or 2 other blast gates open; but you really need to rework the ducting IMHO.

-- Our village hasn't lost it's idiot, he was elected to congress.

View clagwell's profile

clagwell

312 posts in 675 days


#4 posted 09-30-2020 09:50 PM

I think it’s the flow limitation of the 4” lines that’s a big part of your problem. Long 4” flex drops and 4” machine ports are the major resistance in the system so the 8” main doesn’t have enough velocity. 4” SHORT drops and 6” main is a good combination as are 6” drops with an 8” main. There’s just too large a difference between the 8” and 4” to maintain sufficient flow in the larger pipe, even in a horizontal run.

To work with what you have, you might add an 8” blast gate at the far end of the main and open it for a short time periodically to allow the dust collector to clear the main.

-- Dave, Tippecanoe County, IN --- Is there a corollary to Beranek.s Law that applies to dust collection?

View xedos's profile

xedos

106 posts in 183 days


#5 posted 09-30-2020 09:52 PM

If we’re talking about the JCDC-3, then I don’t doubt you have issues with an 8” trunk.

That unit seems to me to be a Spec Whore that doesn’t look quite as good as advertised when the lights are on. 1250 CFM isn’t exactly a big number with the lights out either.

Get yourself an anemometer and measure the flow at the various openings. You need 3500 FPM in the trunk the entire length and 4000 FPM at the tools to keep waste in the airstream. Clearly you’re not getting that in the trunk.

You’re collector isn’t going to support 8” for the entire trunk line. No way , no how. A typical system would size down to 6” after the first couple of drops. and then again to 4” for the last. Might even need 6” after your first drop.

Why reinvent the wheel with an inline blower ? How are you even going to control it ,in tandem, with the cyclone ?

Smaller ducting – better , faster , cheaper. And cleaner.

View EarlS's profile

EarlS

4009 posts in 3231 days


#6 posted 09-30-2020 10:24 PM

If I read your ide correctly, you want to put a blower at the end opposite the DC? That will make positive pressure in your duct and you will blow the dust out of the equipment hooked up to the DC duct work. You will also probably over amp your DC fan motor and cause it to trip out.

Your problem is with your duct diameter as others have said. In order to move and suspend the chips and dust you need velocity which is: flow rate (ft^3/min) divided by the cross sectional area of the duct (ft^2) = ft/min. There are plenty of tables out there that provide minimum velocity tables for saw dust and wood chips.

-- Earl "I'm a pessamist - generally that increases the chance that things will turn out better than expected"

View pottz's profile

pottz

11708 posts in 1867 days


#7 posted 09-30-2020 11:21 PM

i agree with all, 8” wow are you running a commercial shop,that seems very excessive.i have a 2hp jet with about a total of 60’ on two lines of 4” and i have little problem collecting off my 15” planer or table saw.

-- working with my hands is a joy,it gives me a sense of fulfillment,somthing so many seek and so few find.-SAM MALOOF.

View Redoak49's profile

Redoak49

4919 posts in 2871 days


#8 posted 09-30-2020 11:41 PM

I believe the 8” duct is just too big for that DC . The air flow from a 4” pipe is too low in the 8” duct.

View CaptainKlutz's profile

CaptainKlutz

3722 posts in 2377 days


#9 posted 10-01-2020 12:03 AM

If we re talking about the JCDC-3, then I don t doubt you have issues with an 8” trunk.
That unit seems to me to be a Spec Whore that doesn t look quite as good as advertised when the lights are on. 1250 CFM isn t exactly a big number with the lights out either.
.....
- xedos

+1 Specs for Jet 3HP cyclone do not make sense. 8” duct is pipe dream. haha?
Most 2HP canister DC without cyclone have same 1200cfm performance and recommend a 6” duct max?
IMHO – 8” duct belongs on 5HP+ DC, not a 3HP. Either need a larger DC or smaller duct.

+1 A 4” hose only allows ~450cfm air flow with typical SP/flow.
Either need to upgrade the machines to use 5/6” plumbing with minimal resistance, or keep a ~3” line wide open down stream; to raise the duct airflow/velocity to keep dust moving.

IMHO – DC is PIA due all complications.

Best Luck.

-- If it wasn't for bad luck, I wouldn't have no luck at all, - Albert King - Born Under a Bad Sign released 1967

View Fred Hargis's profile

Fred Hargis

6502 posts in 3376 days


#10 posted 10-01-2020 10:31 AM

What’s next, Ol chief?

-- Our village hasn't lost it's idiot, he was elected to congress.

View Russell Hayes's profile

Russell Hayes

25 posts in 61 days


#11 posted 10-01-2020 01:56 PM

That first elbow you mentioned needs to be gradual. You could be losing a lot of velocity there.

Like others have mentioned if you only have one 4” gate open at a time you are starving the system of air. An 8” pipe has the same surface area as four 4” pipes. But I doubt you have the CFM for that. But try 2 or 3 open gates and see if it clears the chips.

40 foot is a long main too. If you have your big chip producers closest to the DC and dust producers further it’s better.

-- Have a hobby? You should have a business.

View OLCHIEF's profile

OLCHIEF

44 posts in 264 days


#12 posted 10-02-2020 05:02 PM

Thanks for all the input. I ordered an anemometer-am going to measure things at various points to see if I can nail down the point of the problem. My jointer and planer are near the DC and seemed to be moving things along at a high velocity-I filled the collector drum quickly with large jointing and planning sessions.. Likewise the table saw was clearing out quickly. My problem seemed to start after routing large, long lock miter joints with a large bit further upstream from the DC. I don’t want to replace all the 8” pipe if I can avoid it but if all else fails and that’s what it takes, so be it. I had not considered that a blower at the upstream end might overwork the vacuum motor. I’ll let you know here when I figure it out.

-- OL CHIEF, Florida Panhandle

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