DC...wow what a headache

[Ole Anderson]

David,

Here is the spec with references on the Oneida filter for the 2 hp Super Dust Gorilla. They claim to be HEPA. 95 sf doesn't seem to be very much area, but mine seems to work fine, I can't imagine a major mfr like Oneida would install a filter too small for their unit.

Filter Media
- Item FCS133695HF
- 13" x 36", 95 Sq. Ft.
- GE Certified H12 HEPA media
- MERV Rating: 16+ - http://www.oneida-air.com/PDF/merv.pdf
- 99.977% efficient @ 0.3 to 0.5 microns
- Third Party Tested - http://www.oneida-air.com/PDF/gehepa.pdf
- Made In The USA!

[David Kumm]

Ole, I didn't say the filter area of the Oneida Hepa media was inadequate, only that the higher efficiency filters created a greater pressure drop so the fan and motor need to compensate, particularly as the filter fills. My tube filters and nano cartridges both get the dylos .5 micron count into the 300-350 range. Maybe someone with the hepa type and a dylos can compare numbers. Dave

[Ole Anderson]

I agree. According to the test data on the filter for the 2 hp unit, you will get 0.5" of loss at 475 to 950 cfm with a clean filter. That is really not too bad if it were in the 800 cfm range with a seasoned filter. It ends up being a numbers game. Maybe some day I will install a manometer, an amp gage, get an anemometer and a dylos and play around, but for now I am happy with the performance of mine as is. Didn't mean to contradict.

[David Kumm]

Ole, I've seen that data too and have a hard time believing any filter that actually filters creates so little pressure drop. Not meaning to imply the numbers are wrong, just can't figure them out. It would be nice to know how any type filter reacts to loading and the range of resistance at a given cfm. I'm probably the only guy on the planet who cares though. Dave

[Michael W. Clark]

The pressure drop will be related to the air:cloth ratio (CFM/ft2 of filter) and how efficient the filter is. The HEPA filters have a higher pressure drop than a lower efficient filter. As you increase the CFM (velocity) across the filter, the pressure drop "usually" goes up linearly. I.E., if you double the flow, you double the pressure drop. The pressure drop also increases as the filter gets dirty. I've worked on some HEPA filters located downstream of industrial baghouses, most of them provide an alarm when the DP gets to around 2"wg. A true HEPA is very expensive. According to the Oneida spec and Merv chart, their filter is not a certified HEPA, correct?

[Peter Aeschliman]

You guys aren't helping the OP's headache!!!

There are many factors at work here and the engineers among us seem to love this topic... And I'm glad they do, because I don't want to do the thinking it requires. And since I don't have the patience, knowledge, or intelligence to do that thinking, I believe it's prudent to rely on the experts and the data, instead of my own emotions about whether the engineers are over-reacting. Better safe than sorry... So I defer to the experts.

What I take from all of it is that we need to do our best with our available means.

• 6" ducts, especially for machines and operations that put off fine dust,
• Hoods that collect dust as close to the source as humanly possible

• high powered DC's (3-5HP with big impellers) that we either vent outside or use separators and filters for.
  
  • If you can't vent all sawdust outside, you'll need a good separator, and high efficiency filters, and a powerful motor (5HP)
  • If you can vent everything outside (course and fine dust) then you probably don't need as big of a motor and you'll save yourself a lot of cash. All you really need is a motor... no filters, no separator, no super duty 5HP motor. Yes, venting outside will make your shop less energy efficient if you require heat and/or A/C.

• Air scrubbers to catch some of the stuff that your DC missed so you don't continually breathe it in. Doesn't hurt to have the extra insurance, but don't rely on it as a primary source of dust collection.

Perfect dust collection is not in the realm of possibility for most weekend warriors, but if you aren't doing woodworking 40+ hours/week, then you have less exposure to dust... so your risk is lower than the professionals.

[David Kumm]

Michael, that is my understanding as well. They come short of claiming it as a true certified hepa. My understanding is that the filtration is very good but don't have any info regarding how it performs over time. They post some numbers on their site. I'm not sure if they are for the actual filter or for the GE material bonded to the spun bond. Perhaps someone who has talked to them has better insight. Dave

[Ken Fitzgerald]

I have a 3HP Oneida Super Gorilla DC which I have manage to use with all my major tools (table saw, bandsaw, OSS, lathe, jointer, planer) and even adapted it to work with my Dewalt ROS. My shop is 30'x24' with 10' ceilings and I have 2 Jet air filtration systems pointed in opposing directions so the circulates, in theory, in a CCW direction. I use the DC and the air filters while I'm sanding and then set the timers on the air filters to run for 2 hours after I am done sanding.

I am pleased with how it works.

[Michael W. Clark]

Back to the question, I'm in the camp of using the low A/C ratio of 2:1 like was originally referenced. If you have a "high efficiency" cyclone, all the big stuff will be pulled out, leaving only the fines. The more efficient the cyclone, the finer the dust particles on the outlet. The fine stuff will blind a filter quicker, therefore you lower the air velocity through the filter to help prevent plugging.

I'm sure there are plenty of users who are running systems with a 15:1 A/C ratio on "Hepa" filters and the system is "working". Just remember, as the filters plug, you are moving less air, which means you are capturing less dust at the hood, and relying on the ambient air filter more heavily.

[Russ D Wood]

I don't have any issues about DC. It even keeps up with my 24 inch planner but the planner does require frequent bag dumps! Russ

http://www.woodmastertools.com/NS/ac...ail.cfm?PID=88

[Dave Sims]

Almost 5,000 cfm? Is that thing for real?

I could save shipping with Onieda. I would have to pay sales tax though, so it would pretty much be a wash.

What really mixed me up was that the Onieda systems that I was interested in had a air/cloth ratio much higher than what Bill recommends.

[Ole Anderson]

You guys aren't helping the OP's headache!!!

There are many factors at work here and the engineers among us seem to love this topic... And I'm glad they do, because I don't want to do the thinking it requires. And since I don't have the patience, knowledge, or intelligence to do that thinking, I believe it's prudent to rely on the experts and the data, instead of my own emotions about whether the engineers are over-reacting. Better safe than sorry... So I defer to the experts.

What I take from all of it is that we need to do our best with our available means.

• 6" ducts, especially for machines and operations that put off fine dust,
• Hoods that collect dust as close to the source as humanly possible

• high powered DC's (3-5HP with big impellers) that we either vent outside or use separators and filters for.
  
  • If you can't vent all sawdust outside, you'll need a good separator, and high efficiency filters, and a powerful motor (5HP)
  • If you can vent everything outside (course and fine dust) then you probably don't need as big of a motor and you'll save yourself a lot of cash. All you really need is a motor... no filters, no separator, no super duty 5HP motor. Yes, venting outside will make your shop less energy efficient if you require heat and/or A/C.

• Air scrubbers to catch some of the stuff that your DC missed so you don't continually breathe it in. Doesn't hurt to have the extra insurance, but don't rely on it as a primary source of dust collection.

Perfect dust collection is not in the realm of possibility for most weekend warriors, but if you aren't doing woodworking 40+ hours/week, then you have less exposure to dust... so your risk is lower than the professionals.

In my opinion if you are using a 3-5 hp system, you ought to size your main runs with 7" or 8" pipe in order to move the air your blower is capable of. I ran a 7" main with my 2 hp unit. Otherwise you are using your horsepower to overcome pipe friction losses instead of moving more air. And don't forget a respirator of at least n95 quality for operations that you are not able to catch all of the dust (sanding large items) or when you are emptying your bag.

[David Kumm]

I agree with Ole in using 7 or 8" mains with a 5 hp 15-16" impeller. You can pull 1200 cfm or so in 6" pipes but with the same system and larger mains move up to 1400-1600 cfm and get more airflow through the smaller machine ports as the overall SP is less. Kind of like opening up the intake and exhaust of any car. Within reason. You need more filter area when you do that as well. Dave

[Brian Tymchak]

..Maybe I missed something in Bills literature, or am missing the concept all together, but there is nothing manufactured that will save my lungs except a clearvue cyclone?...

Along with the technical advice you've received on DC design, IMHO, adequate (good for lungs) dust collection in the shop is not going to be solved by a single DC, regardless of it's hp, design, etc. Sure, bigger is going to be better than smaller, and get the best you can afford, but, I suggest you also consider getting an air cleaner (or 2 depending on your shop size) as Ken suggested, and also a positive air respirator. I originally got the Trend Pro Airshield to start turning, but I quickly decided to use it when I sand and am at the tablesaw, especially with really dusty materials like MDF. I can definitely tell the difference in my breathing after a stint in the shop compared to before I had the Trend Pro.

[Ole Anderson]

Sometimes the shop isn't the best place to work on a project, case in point: I needed to refinish the slotted Teak swim platform on my 23 year old boat. Lots of power sanding involved and there was no way to do it in my shop and catch most of the dust. And Teak dust can be irritating. So I set up a couple of sawhorses outside on a breezy day, slapped on my mask and went to work, first with my belt sander with 50 grit, which has no dust collection, then 120 and 220 on my 6" ROS, again no dust collection, then a stick with PSA 180 to get in all of the slots, then I did a small roundover on everything with a trim router, then hand sanded everything. 3 hours later I got out my gas powered lawn blower and blew off the patio. Man I wish I could use that thing in the basement shop. Now I am in the process of applying at least 4 coats of teak oil 24 hours apart, in the garage where I can get good ventilation.