Dust Collector Performance Question

[MarkSLSmith]

Hi all, 

For 25 years or more, I've been using a Powermatic Model 73 dust collector.  Approximately 10 years ago, I added an Oneida cyclone and a Lee Valley filter bag.  You can hardly recognize the original dust collector.  When I first purchased it, it was the most powerful dust collector that I could power with a 110 V outlet.

Anyway, my question is this.  I'm thinking to upgrade to a new Oneida V3000.  My thinking was that the Oneida would probably blow the doors off (suck the doors off?) the old Powermatic.  Last night, I pulled out the PM 73 owners manual to look at the specs.  The PM 73 lists 900 cfm at 10" static pressure.  Oneida provides a chart; at 10" static pressure, it has 600 cfm.  Needless to say, I was surprised by this.

Now, I realize that the Oneida filtration is orders of magnitude better than the PM 73.  Still, I would be really disappointed if I paid a ton of money for a new dust collector, nominally twice as much horsepower, and got less air flow.  

Here's some possible explanations.

1. Powermatic was lying about the capacity.
2. Powermatic and Oneida used such different test methods that it's an apples and oranges comparison.
3. Although the Oneida is marketed as a central dust collector servicing a network of ductwork, users really don't buy it for this purpose and use it connected to one machine at a time.
4. It really is less air flow, and you are really buying it for the filtration capability.

Looking forward to comments.

Mark

[fredhargis]

Mark, quoted performances for most DCs about about as realistic as the 6.5 HP your vac has, or the 3.25 HP of a router. Now let me say, I am not a fan of anything Oneida (had one and moved up to a CV) BUT, their stated CFMs are closer to reality than almost anyone else in the market. So, I think the change for you (I guess that's the 120V version you're after?) would be quite a  step forward. Consider this: the 900 CFM for the PM was a marketing man's wet dream, but then you added a cyclone (increased drag, less airflow), I would guess that after piping that DC is moving maybe 350 CFM. (That is a guess, a wild one.) So the upgrade would be substantial, IMHO.

[jteneyck]

Mark, take another look at the specs on the Powermatic.  No 120V DC is going to pull 900 cfm at 10" static.  It could be the specs actually say the max. CFM is 900 and the max. static pressure is 10".  All good, except they are measured at opposite ends of the fan curve.  

Here's the fan curve for the Oneida V-3000.  




This is a pretty capable unit, but you'll see that the max. CFM occurs at the lowest static pressure, the same as with any DC.  They should list how it was measured; typically it's with a large test orifice a short distance from the fan inlet.  It's a standard method that will never be achieved after the unit is installed, even with just a short length of hose.  It's of no use for real world applications.  The fan curve also shows this unit will pull 600 CFM at 10" static.  Again, this is based the same test process but through a smaller diameter orifice.  The good news is that that piece of information is very useful in designing a workable system.  It suggests that if you can keep the static pressure below 10" it should give you plenty of flow for almost any single piece of equipment you hook it up to.  I'll bet if you look up the fan curve for the PM, it will have much lower flow at any comparable static pressure.  And since you added an Onieda cyclone and a finer filtration bag to it you pushed the static pressure up, a lot.  On the other hand, the Onieda unit has a cyclone and cartridge filter as part of the design, so the fan curve represents real data with a fresh system (before the filter loads up).  

Long story to say, if the Onieda meets your needs it will deliver the performance it's rated for.  

John

[MarkSLSmith]

Here's some comments.

1. I've included a copy of the specs.  It clearly says 900 cfm at 10" static  pressure.

2. I'm not limited to 110 V anymore, so I'm looking to get the best dust collector money can buy.

3. Rather than decreasing performance, adding the cyclone and the LV bag made a major upgrade to the performance of the dust collector.  At least twice as good, in my estimation.  

Thanks, 
Mark

[fredhargis]

Well, I wish you the best with your decision.

[jteneyck]

Here's some comments.

1. I've included a copy of the specs.  It clearly says 900 cfm at 10" static  pressure.

2. I'm not limited to 110 V anymore, so I'm looking to get the best dust collector money can buy.

3. Rather than decreasing performance, adding the cyclone and the LV bag made a major upgrade to the performance of the dust collector.  At least twice as good, in my estimation.  

Thanks, 
Mark

They would have been the first and only company to have ever done that with a 1.5 hp motor.  Adding a cyclone may have improved the overall performance, all that matters in the end, by keeping the bag from blinding over as quickly, but the static pressure went up so the flow went down.  That's OK as long as the flow that remained was enough to move the chips and dust through the duct or hose.  

If the PM performance is actually as stated, going to the Oneida system will offer lower performance (600 cfm at 10" sp, with a 3HP motor), but improved filtration.  Whether or not the performance is still enough depends upon the particulars of your system.   

John

[MarkSLSmith]

They would have been the first and only company to have ever done that with a 1.5 hp motor.  Adding a cyclone may have improved the overall performance, all that matters in the end, by keeping the bag from blinding over as quickly, but the static pressure went up so the flow went down.  That's OK as long as the flow that remained was enough to move the chips and dust through the duct or hose.  

If the PM performance is actually as stated, going to the Oneida system will offer lower performance (600 cfm at 10" sp, with a 3HP motor), but improved filtration.  Whether or not the performance is still enough depends upon the particulars of your system.   

John

Thanks for the comments.

Clarification:  the specifications are for the original machine, not after I modified it.  If I were competent, I might have measured the cfm before and after the modification.  Alas, it was not done.  All I really remember is being delighted with the results of the modification.  

Thanks, 
Mark

[FireWood]

I have a Delta 50-760 from about 2005.  I believe that is pretty similar to your Powermatic.  1.5hp, 120/240, 1 micron bag.

It was advertised at 1200 cfm, but was typically tested to ~900 in magazine tests - with essentially no load.  It also won every magazine shootout at the time for single stage dust collectors, so I do not believe the documented specs on your powermatic. 


Regardless, before I dropped $3K plus on a new DC, I'd find one and go see it, and try and determined if it sucked enough to justify the expense.

BTW, I also have a 2hp Woodsucker cyclone that is a bit older than the Delta.  It definitely pulls harder than the Delta.

[JDuke]

If your looking for the best money can buy don’t rule out clear vue

I don’t have one, but if I were to go to a central system with ductwork that’s the one I would buy.

[rwe2156]

Have you considered the SuperCell?