Dust Extraction

[andreg]

Hello All
Like many of you, I spent a great amount of time reading and learning the intricacies and values of good dust extraction. The cyclone setup interests me greatly.

I have a friend who is a retailer of quality wood machines and is a qualified cabinet maker of some 20 years. He suggested to me that the cyclone type dust extraction is actually illegal (according to the EPA), whilst the bags are legal.

Could anybody shed any light on the subject.

Regards

Andre

[soundman]

I find that very hard to believe.

there are many cyclone units in use out there and respectable vendors selling them.


like many things I would like to see chapter & verse from the legeslation or rulings before I believed such a statement.

[andreg]

Thanks Soundman for your feedback, after which I went to my second step which was to search Google (thank God for Google). If anybody is interested, this url will take you to the EPA guidelines which has some interesting information and also has links to the legislation relating to this issue.

http://www.environment.sa.gov.au/epa/pdfs/guide_joineries.pdf

In a nutshell, cyclones are fine for saw dust and other coarse dusts but a woven bag filtration system is required for finer (moulding/routing dusts).

Regards

Andre

[soundman]

If you look at most modern designs the output of the cyclone is then filtered by either bags or paper filters.

if you havn't already looked check out bill penz' site.

it'll bring you right up to speed.

cheers

[andreg]

thanks, i will. I appreciate your help

cheers

andre

[spbookie]

Hi,

Cyclones should have a filter on the exaust to make sure that the fine dust is collected.

The real advantage of a cyclone is that all the larger particles are removed before the fiilter is reached. This is much more efficient in regards to airflow and allows finer filters to be fitted.

Charles

[Red neck]

I could well be open to debate, but I was of the opinion that the purpose of a cyclone was to slow the airflow thereby depriving larger particles of the necessary support to reach the filter. In other words the larger particles simply fall to the bottom of the cyclone where they are collected. The smaller particles however are carried up and on to the final filter area.

Without the cyclone both smaller and larger particles are carried to the filter, the larger particles falling into the bottom bag.

In both cases the fine particles still make their way to the filter. It is the smaller particles that block the filter bag, not the larger particles.

With these points in mind I would tend towards the argument that the best way to improve extraction efficiency would be to maintain a high airflow through the system to provide the necessary force to carry the particles. Unfortunately many components of a dust extraction system create resistance. Ducts, bends, impeller design and finally the filter. If a cyclone system and a two-bag system are both driven by identical motors, impellers and fitted with identical bags, the efficiency of each system must be identical. And since both filters will recover all the smaller particles they will both block at the same rate. The cyclone will separate the larger particles for easier disposal but will still require emptying of the filter collector for removal of the smaller particles.

Therefore efficiency may be improved by the impeller, power available and filter area. The pleated filters provide many times more filter area than the bag filters. My argument therefore is rather than add cost to the system with a cyclone, it may be more productive to fund a high quality pleated filter. Such filters are effective down to five microns whereas the standard bag is effective down to 30 microns.

As an aside I understand that in the ‘States’ it is possible to purchase efficient and balanced impellers for the Chinese machines. Impeller housings are also up-gradable to provide for six inch ducts to further improve the mass airflow. I look forward to arguments to the contrary.

As a boy I lived close to a sawmill in Brisbane suburbia. The mill had what I now know to be a cyclone. Quite large (about forty feet high) but with nothing more than a tin ‘hat’ on top. Heavy particles fell to the ground where they were collected and dumped in a nearby lake. Fine particles drifted from under the ‘hat’ and into suburbia. No filter. I guess in those days cyclones would not have met the present requirements of the EPA! Andre, perhaps it is those old systems to which your friend refers.

[Grunt]

Both large and small particals block the filter. The cyclone reduces the large fellas from getting to the filter. So it takes longer to block. Means less cleaning and a more efficient system for longer.

If you don't have a cyclone and are routing MDF the filter will be caked in wood dust in no time. Your dust collection system will not work very well any more.

[Helix]

It is not just larger particles that are trapped by the cyclone. *MORE* particles are separated by the cyclone, large and small alike, allowing the bag to perform less filtration.

I am confident that those with cyclones will attest to the fact that they empty a wide range of particle sizes from the collector bin.

[Barry_White]

This seems to be a pretty contraversial subject.

We have a Amway vacuum cleaner that operates on the cyclone principle and it is very interesting on how it works.

See attached picture. The numbered parts are as follows.
1. Gasket Ring
2. Cyclone Tube Assembly
3. Cone Seal Gasket
4. Dust Container
5. Inner Dirt Trap

The cyclone Tupe assembly has two slotted holes in the top in the section between the step and the ring near the number 2 which follow the circumference into the inner tube indicated by the hole on the top which would tend to create a cyclone effect.

The air is sucked in with the dirt through a hole in the top of the cleaner which the Dust Container fits into which also creates a cyclone effect.

The interesting thing is that the cyclone tube assembly No 2 fits down into the inner dirt trap and and is sealed by the Cone seal Gasket No 3

The only air going into the cylone tube assembly goes in via the two slots at the top.

97 percent of the dust and dirt is deposited into the dust container, 2 percent of the fine dust finishes in the bottom of the inner dirt trap No 5 and only 1 percent finishes up on the final filter on the machine which is a foam pad 150mm x 100mm x 20mm with a final filter made of a very thin layer of cotton wool with a fine membrane each side.

The interesting thing is that this machine never stops sucking even when the dust container is chock a block full.

The best test this machine had was in a unit my daugter was renting up the north coast. She had in it was what she thought was pink carpet. She had a new Sanyo sucker and blower she thought did a good job at cleaning.

We tried this machine on the carpet and we had to empty the dust container 4 times in a 2 bedroom basic unit.

What we thought was pink carpet was actually WHITE. It appeared pink from all the red sand and dirt that was in the carpet that the machine removed.

What is the point of all this is that a properly working and designed cyclone will deposit very little dust on the final filter.

[soundman]

As Bill Penz(legend) found there are many misconceptions concerning cyclones and a large number of poor performing examples.

If the cyclone is optimum designed it should extract 95% or better of all particles including those 1 micron or less.

Some of bills infor comes from the cotton industry which produces a lot of fine dust.

The old saw mill cyclones of the past were not designed or capable of seperating fine dust but were probably quite light on for required blower power.

[Red neck]

Grunt,

“…Both large and small particals block the filter…”
Wouldn’t gravity cause the large particles such as shavings and chips to fall into the bottom bag? A 30 micron filter bag would be blocked by particles 30 microns or larger, until such time as the inside of the bag cakes up and improves filtration. Doesn’t help airflow any though.
Helix,

“…*MORE* particles are separated by the cyclone, large and small alike…”
My reading on cyclone systems suggests otherwise. A good cyclone will extract up to 95% of the debris allowing particles 15 microns or smaller only to pass on to the filter. If larger particles are passing on to the filter then the cyclone is not doing its job. Granted smaller particles that temporarily attach to shavings and chips will wind up in the cyclone collector giving weight to suggestions that minute particles are also extracted.
Bazza,
You have highlighted a point that I feel should be pushed home to manufacturers. We as consumers have very little information from dust collector manufacturers to make reasoned decisions. Comparing an Amway with a Sanyo cleaner is similar to the approach most of us make with DC’s. I actually bought a 1hp machine and found it inadequate so went back and bought a 2 hp machine. The retailer won out on that one!
I did say

“…If a cyclone system and a two-bag system are both driven by identical motors, impellers and fitted with identical bags, the efficiency of each system must be identical….”

To compare two machines you would need to assess rated power and impeller efficiency otherwise any argument is null and void. But how are we able to do that in the showroom with the information provided by the manufacturers?
Soundman,

“…If the cyclone is optimum designed…”
You have hit the nail on the head with that statement. A cyclone is not a magic accessory, it is simply an extraction device that uses aerodynamics to slow the airflow and cause the heavier particles to lose support and fall to the bottom of the collector. The most simplistic way I can describe it is like a rapid flowing river, carrying logs and other dense material. When the river widens and slows, the heavier material sinks to the bottom, but the lighter materials flow downstream.

The dust collector impeller provides the suction to extract within the system. It does this by increasing the dynamic pressure reducing static pressure. Dynamic pressure increases with velocity. Therefore any reduction in velocity causes dynamic pressure to reduce and static pressure to increase. We don’t want that.

A good system creates sufficient pressure reduction to move the air at around 4000 feet per minute in the main duct and around 3500 in the branch lines. Elbows, gates, pre-separators all help slow down the airflow thereby raising static pressure. This could affect impeller performance since it would be designed with specific pressure considerations at a given RPM.

An ‘optimum designed’ system would be one with the impeller, motor and cyclone matched to each other, and able to meet system requirements given inherent dynamic pressure losses in the ducts, elbows and other components.

Duct velocity is extremely important to move all the debris. Unfortunately velocity may also detract from performance as the greater the velocity, the more impact resistance will have upon its efficiency.

Therefore my argument was to improve the overall system with better filtration, ducts, impellers and the like before incorporating a cyclone. I still believe the cyclone is something of a luxury in the average 2hp system.

Finally I think we are being sold short by DC manufacturers as the only information we receive from them is the CFM rating and the HP of the machine. This tells us nothing about machine efficiency. Very few manufacturers provide a CFM/static pressure Fan Performance Curve. With this information and given the available data on static pressure loss through various ducts, elbows, gates etc., the consumer would be better able to purchase a DC tailored to individual system requirements.

[soundman]

In the last few weeks since Ive been invistigating the dust extraction upgrade options I have been stunned by some of the attitudes that seem to be arround.
And the variation in those attitudes.
And this includes all levels and areas of the matter, users, vendors & regulators.

from the realy blody minded "ho cares" to those who want to sell small shop operators dust extraction systems worth more than their worldy goods.

What disturbs me the most is that almost without exception, what is most economicaly viable & properly effective is the last thing on peoples mind.

preconceptions, vested interset, & ignorance seem to prevail over properly considered resason & the desire to do what is best & achievable.

No matter what you say some people ( especialy certain regulators) will not believe that a properly designed & properly post filtered cyclone can be effective.

I dispair for the small shop operators. Are we condemmed to suffer the two bag & blower units with their afterthaught fixes for ever.


:mad: