Cyclones and Dust Collection

[Ken Krawford]

Recently I experienced a complete lack of suction in my dust collection system. It is a DIY system based on the Bill Pentz design http://billpentz.com/woodworking/cyclone/.

Since I knew my chip barrel was nearly empty I immediately figured that my filter must be clogged. For those not familiar with this system, the filter is a 12" x 34" cartridge style pleated filter. Since these cartridges are ~ $150 + shipping, I usually just put my shopvac in the center of the cartridge and blow the outside with my compressor blow gun. Hours later I'm still blowing out trapped saw dust.

Do anyone have a better/more efficient way of dealing with fine dust in a cyclone type collector?

[Bob Wingard]

Plug the leaks !!! Seriously ... the only way dust will get to your filters is if it's not spun out of the air in the cyclone ... and, in a properly designed system, that only happens if there are leaks that allow the dust to remain airborne. Find and plug the leaks, and it should go away. It will also happen if your collection bin is full, and the debris has no place else to go, but, I'm assuming you've kept an eye on that.

[David Kumm]

There will always be dust in your filters. Wood cyclones are designed for >30 micron and larger particles and are generally less than 50% efficient at less than 10 microns. Cyclones designed for fine dust are expensive to manufacture and create a greater pressure drop so you need to compensate with a larger impeller. If you run a wide belt or drum sander you could bypass the filters and go outside, continue to blow them out with air, or put on bags. Chips in the filters are a different problem and should not occur. Dave

[Wade Lippman]

Quite a difference of opinion; one saying cyclones catch almost nothing, another saying they should catch everything.

My old cyclone, a 3hp JDS, put about one cup of fines in the filter per 55 gallon drum. Magazine test reports said it was relatively inefficient, so a good one should do less than one cup.
It never clogged; I cleaned the filters once a day because it did it automatically when I turned the main power off. (during the day I had a relay on the blower, so the automatic cleaner didn't come on all the time.)

My new Grizzly has much less than a barrel so far, so I don't know how it is doing; but it is much longer than the JDS so it should do better. But I've done a third of a barrel without cleaning the filter and the suckage is as good as new; so I am optimistic.


So, based on my experience, you have a problem. Leaks? Horrible design? I don't know, but a problem.

[David Kumm]

Did not mean to say that cyclones don't pick up anything. They help considerably but don't expect miracles with fine dust. If you run a widebelt or drum and get one cup a day you are doing well. If you believe the cyclone catches fine dust, squirt some chalkline dust into a port and look at then inside of your filters. They will be colored along with the waste drum. A cyclone will slow down the need for cleaning though. the cfm does need to be matched to the cyclone for the best efficiency. Dave

[Michael W. Clark]

I would also say check for leaks around the dust bin and cone discharge. Any leaks will cause re-entrainment and kill your efficiency.

As David said, cylones are not necesarily the silver sword. The amount of dust you carryover is going to depend on the efficiency your cyclone and the size of the dust being collected. Cyclones operate on an efficiency curve. They are more efficient on large particles, and less efficient on small particles. The better the cyclone, the more efficiency you get on small particles. If you are dealing mostly with planer, jointer, table saw dust, then you will have less carryover than if it is getting a steady diet of dust from a sander.

As far as dealing with your problem, I would figure out a way to not let the dust bin get to full, and to put a pressure gauge on the outlet of the fan to monitor filter pressure drop. If your dust bin at the very bottom of the cone, you need to leave some free space in the top, do not fill it all the way up.

Mike

[Ken Krawford]

Thanks for the replies. My system is pretty tight, especially around the dust bin and cone discharge. After reading the posts I realized that I have been doing a lot of sanding on my wide belt sander recently. Couple that with it being a long time since I last cleaned the filter and I think that's my problem.
Is my filter cleaning method acceptable or is there a better way?

[ian maybury]

+1 that cyclones are right on the limit so far as the fine end of woodworking dust is concerned, and that in that situation they do pass some significant proportion of it. Which means that even with a well set up and well optimised cyclone set up doing a lot of sanding and the like is going to lead to a need to clean filters more frequently.

The recognised technique for cleaning high quality spun cartridge filters unless somebody has come up with something new is basically to use a compressed air nozzle from a safe distance (closer blasts apart the fibres in the filter and allows serious leakage), while tapping the outside with your hand and vacuuming from the inside/the collection tray. The various sorts of wipers or brushes also screw up the filter so that it leaks. Here's a couple of discussions on the topic including from Wynn filter:



There's solid information somewhere by i think Bill P setting out how it's not possible to remove all the dust from a filter. He describes how it results in the back pressure and the degree of leakage building up from cleaning to cleaning until replacement becomes necessary. It's said too that it's highly inadvisable to allow filters to clog (that frequent but light cleaning is advisable) - because the increased pressure drop causes the dust particles to be driven deep into the weave so they cannot be removed, and so they cause leaks.

The other basic is to make sure you have plenty of cartridge area (that's twin 250 - 300ft2 cartridges on a 100cfm + system) - this minimises the pressure drop, extends the life between cleanings and minimises all of the above effects. Discussed by Bill P at G8 on this page: http://billpentz.com/woodworking/cyclone/dc_basics.cfm

It'd be interesting to hear from some longer term users of cyclone system how long their cartridges last for...

ian

[David Kumm]

Every cartridge or bag is rated for CFM- per cartridge or per sq ft. People who know filters can also tell you what type surface loads and cleans the easiest, and how to best clean them. Some dust left in improves the filtering and there are some good threads here about building gauges to monitor the pressure drop so you know when to clean. Dave

[Jim Neeley]

[QUOTE=ian maybury;2103201The other basic is to make sure you have plenty of cartridge area (that's twin 250 - 300ft2 cartridges on a 100cfm + system) - this minimises the pressure drop, extends the life between cleanings and minimises all of the above effects. [/QUOTE]

For the benefit of the OP:

Ian,

Wasn't that a typo above? Did you intend to say that around 1000 CFM you move from one to two cartridges?

Jim in Alaska

[David Kumm]

For the benefit of the OP:

Ian,

Wasn't that a typo above? Did you intend to say that around 1000 CFM you move from one to two cartridges?

Jim in Alaska

Depends on the cartridge. Wynn nanofiber used on clearvue and others are rated at 500-600 cfm each so you add every 500 cfm. They are a tight pleat cartridge with about 300 sq ft of area each. Dave