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Forum topic by scribble posted 07-19-2018 08:24 PM 703 views 0 times favorited 2 replies Add to Favorites Watch
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scribble

197 posts in 2400 days


07-19-2018 08:24 PM

Topic tags/keywords: question

I am currently running an older Delta Single stage dust collector with a home made thein baffle/separator. I have been watching numerous videos and reading lots of articles about how the cfm increased when going from the thein to a SDD will increase CFM as well as changing the air filter will get you more CFM. I contacted oneida and they said there product will not increase suction just make my bag filter/ air filter not fill up as fast.
I guess im looking to see if the SDD is worthwhile in everyone’s opinionor would my money be better spent on a filter upgrade?

-- If you can't read it Scribble wrote it!! “Experience is merely the name men gave to their mistakes.”


2 replies so far

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ArtMann

1139 posts in 1015 days


#1 posted 07-19-2018 08:34 PM

Going from no separator to a separator will decrease your cfm, no matter which one you use. I doubt very much that the Thein is better than the SDD and probably isn’t as good. The benefit of the SDD is that it is reported to be considerably more efficient at separating out fine dust. That will reduce the frequency of cleaning your filter.

View BobAnderton's profile

BobAnderton

283 posts in 2989 days


#2 posted 07-19-2018 11:15 PM

It’s a simple question that broaches a bunch of complex topics. Just free forming here, some of which you asked about and probably some of which you didn’t, and already know, so forgive me.

Is a SDD cyclone going to be more effective at separation and/or cause less static pressure drop (CFM drop) than a thein baffle separator? Maybe, but not necessarily. There’s a trade off between how much pressure drop occurs and how high the separation effectiveness is. I’m sure the smart folks and Onieda did a good job striking what they felt was the best balance in designing the SDD, but you could get what you think is a better point on that trade off curve with a thein separator.

Will a 300 square foot .1 micron pleated filter give you higher CFM than a 50 square foot 5 micron bag? Maybe, but not necessarily. Yeah, it’s more square feet of media, but it also passes less air per square foot of media surface because it’s a finer filter. Is the filter only a small portion of the static pressure drop your fan is pushing against anyway? The filter may only be a 1/2 psi of drop at the flow rate you are getting if you’ve got a separator and ductwork also inline with the fan. Those other factors may be causing 4-8 psi of pressure drop, in which case the filter change won’t make much of a difference. The finer pleated filter should be expected to give you cleaner air being discharged from it since it has a higher rating. Nobody publishes curves of pressure drop vs CFM for various filter options, which would be a clear way of comparing them. It’s further complicated by the fact that the dust cake on the filter does a good portion of the actual filtering and causes a good portion of the pressure drop. Performance of a clean filter isn’t the relevant curve for real world use.

A separator, whether it’s a SDD or a thein, does cause a lot of pressure drop, no doubt about that. Which causes more? Depends. Which separates better? Depends. The pressure drop of the separator is presumably worth it because it prevents the filter from getting so clogged very fast. The average CFM could be higher with a separator than without because the filter is not too loaded up with the separator in place, and could be too loaded up a fraction of the time without the separator. Think of a plot of CFM vs time. With a separator maybe it’s a pretty flat line at, say, 600 cfm. Without a separator (thein or SDD, it doesn’t matter) it’s more of a sawtooth form with the peaks when you clean the filter. The peaks are probably higher than 600 and the troughs when the filter is loaded are probably much lower.

There are lots of design parameters that affect the separation and pressure drop as a function of CFM for both thein separators (of many types) and cyclones. Maybe you’ve got a pretty good thein separator that performs about as well as a SDD. I’m sure the SDD is a pretty good cyclone for the flow rate it’s designed for but it has to find a balance between the tradeoffs just like the thein separator does. Maybe you’ve got a pretty suboptimal thein separator and the SDD will be a big step up.

The biggest thing, in my opinion, you can do to improve your CFM performance without getting a bigger impeller and motor, is to reduce the pressure drop of your ducting and tool ports. Make runs short. Go to large diameter (like 6” makes a huge difference). Minimize flex hose length and number of 90s, and make those large diameter sweeps.

-- Bob Anderton - Austin, TX - Nova 3000 lathe, Alaskan Mark III mill, Husqavarna Saw

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