Cyclone dust collection on shop air filter

[Mark Hultzapple]

Hi everyone,
A friend ask me if I ever saw a cyclone collection setup for a down draft sanding table. He would like to use a large squirrel cage blower to move enough air to create sufficient flow to capture airborn particles through out his 30 X 30 shop. He would like to employ the cyclone idea to separate as much dust as possible prior to the filters to maximize time between filter cleaning and changes. I have seen down draft table designs on this forum using furnace blowers but the designer used furnace type filters. My friend is concerned furnace filters would clog too quickly for the amount of dust he creates. He also wants to let the filter run continuously to clear the air while he's in the shop. Anyone have any ideas on this? Would a cyclone system work connected to a furnace blower?

[Jim Becker]

I do not believe that the squire cage blower is going to provide the type of airflow you will need to work efficiently with a cyclonic separator.

[Robert Payne]

I would use the squirrel cage fan to build a separate shop air filter and use good filters and a timer control on it to remove airborne dust. A downdraft sanding table produces lots of fine dust so your best bet is to send it to your dust collection system -- preferably a cyclone.

I'm in the process of installing new ductwork and a ClearVue Cyclone in my shop and I plan to convert/upgrade my tablesaw outfeed table top into a downdraft sanding station that will be hooked to the cyclone.

[Randy Denby]

A common household type squirrel cage blower is designed for less than 1" of static pressure....usually 0.1 " . In a couple of books I have on sizing dust collectors and ducts, they stated to figure 2" of static pressure drop across a cyclone. (This is for a stand alone cyclone ahead of the fan ) I'm sure the newer more efficient cyclones being built nowadays are a little less restrictive, but no where near enough to work with that squirrel cage. A cyclone uses a centrifugal impeller with backward tilting vanes and can pull up to 10" static pressure ...or resistance to flow in the hobbiest /small shop type of cyclones.
But another point would be, the fine dust in the air would best be served by your friends squirrel cage as it will probably have a very high cfm rating and can move alot of air. For example, a 3 ton squirrel cage are generally rated at 1200 cfm....with a 20'x30' x10' shop (6000cu.ft) you would be recirculating the complete shop volume of air every 5 minutes thru the filter. So, my best advice would be to collect as much dust at the source of machines /downdraft table with a cyclone, then any other dust that escapes from the machines and into the air will be better served by using the squirrel cage with a large pleated filter bank and have cheaper prefilters that can be either washed or replaced. The larger you can make the filter rack the better you'll be as it wont clog as quick nor be as restrictive...

[Mark Hultzapple]

I thought there would be a good reason why I haven't seen the cyclone idea yet. Thanks for the input guys and I'll pass on the info to my buddy.

[Chuck Lenz]

Cyclones are more effective for heavier particles, like chips. I'm not saying they won't do a good job of filtering out fine particles, but I think you will find out that there isn't much fine dust at the bottom of a cyclone, most of it will go to the bag or cartridge filter.

[Jim Becker]

Cyclones are more effective for heavier particles, like chips. I'm not saying they won't do a good job of filtering out fine particles, but I think you will find out that there isn't much fine dust at the bottom of a cyclone, most of it will go to the bag or cartridge filter.

Not true, Chuck...surprising as it may be. I get very, very little fines that get by the cyclone, itself. Almost nothing in the collection tray under the filters.

[Chuck Lenz]

Jim, I guess I was going on the principal of the plastic garbage can lid, you know, the best money can buy. ;) I should of known better. I apologize for misleading a fellow Creeker up the creek. :o

[Jim Becker]

Yea, a little different, Chuck. And heck, you can totally clean out that trash can cyclone with a little extra CFM!!!

With the "true" cyclone, the design spins the air (and consequently the material), but as it passes down and gets to the "cone", friction, etc., starts to slow the air down and the material drops out...including a surprising amount of fine material.