Thread: Want your DC checked for invisible dust?

You may well find the better of the truck air filters pretty danm good, they are not much concerned with "Invisable Dust" but when a truck engine is work as much as a small house, people tend to go to some length to extend it life.

Back in the early days, "The Pentzmeister" was using or recommending truck air filters for the outputs of his cyclones, because "the proper thing" was either rediculoulsly expensive or hard to get.....and he reconed they did not spec up too bad at the time.

Have a look at the landcruser filter......you would be surprised where landcruser parts end up, because if you can get anything you will be able to get a landcruser part.

As you say...old mate may just need a new set of filters in his vak......possibly optomistic..but a realistic expectation.
What may also be the case is that the machines may simply need cleaning and putting back together properly..leave one seal or rubber washer out or put something back the wrong way arround and the whole filtration performance will go down the toilet.

I have even see people using industrial vaks without the filter installed......if running them wet some require the filter to be removed...gets lost and never reinstalled.

cheers

Originally Posted by soundman

It stands to reason that the thinner the filter membrane the more inclined it will be to this behaviour.

It also occurs to me that a filter made of paper that performs just fine, may exhibit this problem if it is damaged in the folding process or it does not tolerate folding well.

If you look at some of the better pleated cartrige filters you will see the paper is folded around a curved edge mandrel, some chepaer items I have seen have very sharp folds, this must compromise the paper.

I would be very interested to see how cheap chinese pleated cartrige filters perform compared to locally made industrial grade units made from specified paper.

cheers

I can't give you any real data on the performance of the paddle cleaning filter that comes with a dusty compared to an industrial filter directly but talked to a filter cleaning service owner. I had some industrial filters that were tossed from work and took them to be cleaned. When I picked them up he told me that he won't do the home dusty ones because they fall apart in his machine whereas the industrial ones can be cleaned up to 4 times and still meet the makers flow and filtration specifications. That tells me enough about the quality and performance of the two.

McWinn Chilliwack Industrial Air Filter Cleaning
(The ones I have are like the oval shapes in their Photo Gallery.)

Pete

I'll have another go these....Cartridge Filters

$375 per pair ex stock in Oz. BTW they are US made, not Aisian. No one can supply a filter cheaper to that spec that I know of.

It would be my suggestion that anyone who has technical questions concerning filters email Rick Wynn (Wynn Environmental) in the US. He has an enormous knowledge of the technicalities involved and is always more than willing to help.

Today I tested 3, 1HP DCs, and a vacuum cleaner in a rural/bush location about 100 km from the city. The background particle count both outside and inside the shed was not that different to the levels I measure on sundays at my place (inner city).

The workshop was 8 x 8 m with a roller door that opened up a complete wall facing a wide veranda onto which machinery and DCs could be wheeled.

Two of the upright DCs had pleated filters (PF1 and PF2) and cloth bag bottoms (CB1 and CB2) while the 3rd had a single horizontal cloth bag (CB3)

The upright DCs were >30% full of dust while the other had <10% of dust in it.

The vacuum cleaner was a in-house branded cleaner with a paper bag and pleated filter.

Both pleated filters both had as expected very high efficiencies.
We cleaned PF2 by rotating the paddles 3-4 times and this time the filter efficiency went down for the finer particles.
The result for the vacuum cleaner was as expected except for the larger particles which could have been a result of contamination on the outside of the VC


Both cloth bags connected to the upright bag DCs had as to be expected poor efficiencies with one generating substantially more dust than it sucked in.
The high efficiency for CB3 was probably because it was connected to a sander and was very well seasoned. In contrast to upright DCs which swirl and mince the dust inside the bags the dust in CB 3 just slams up agains the cloth bag and self filters. This of course stymies the flow but that very important aspect of DC is not part of this study.



The recommendations to the user were pretty straight forward. Replace CB1 and CB2 with plastic bags. CB3 is a single bag so it cannot be replaced by plastic.

Once again I would like to reiterate that these efficiencies are only one part of complex picture.
For example even though the filters are very efficient 1HP DCs are not very efficient collectors of dust at source so having high filtering efficiencies at the DC is not that useful.
This particular user has a big advantage in being able to open up a complete wall of his shed.

Again we see people spending good money on pleated cartrige filters and not replacing the bottom bag with plastic.

Most suppliers I see advertising after market pleated cartrige filters, include plastic bags for the bottom in the deal......so what gives.

No measurements required to see what is wrong here and where the dominating limitations and risks lie.

1hp extrators may not be ideal for producing air flow at point of capture, but a properly 1hp extractor with a pleated cartrige filter would have to be a better proposition that any other dust extractor that has plain cloth bags that continuoulsy despense fine dust into the workshop.

cheers

One thing I find very curious is that some of these filters seem to pass largish material in the 2 to 5 micron and larger range while holding back finer material.

one would expect that the efficiency would universally suffer as the particle size gets smaller.......why is it so?

Another taught is...how does the composition of the dust entering and within the machine influence the figures measured comming out of the machine.

perhaps with some of these machines, the fine dust or a large portion of, has already blown thru the filter, leaving predominantly coarser material to be measured.

Perhaps reality is worse than the instruments indicate.

It occurs to me. the only difinitave way to test these filters is with "known dust".......where do we get that from?

cheers

Originally Posted by soundman

Again we see people spending good money on pleated cartrige filters and not replacing the bottom bag with plastic.

Most suppliers I see advertising after market pleated cartrige filters, include plastic bags for the bottom in the deal......so what gives.

No measurements required to see what is wrong here and where the dominating limitations and risks lie.

I agree it's a no brainer but while I may be optimistic, you seem to have unrealistic expectations about what people believe - ie they generally only believe what they see.
It's only when I show them the counts on the particle counter do they even start to believe and even then they are not sure.
Anyway it does not matter, the two two examples I have shown plus other people that I have demonstrated this to have all gone off and bought plastic bag bottoms.
Not only that but to demonstrate the power of anecdote they have told others who have copied their mates.
They all acknowledge the testing has been worthwhile and that they have learned something.

Originally Posted by soundman

One thing I find very curious is that some of these filters seem to pass largish material in the 2 to 5 micron and larger range while holding back finer material.
one would expect that the efficiency would universally suffer as the particle size gets smaller.......why is it so?
Another taught is...how does the composition of the dust entering and within the machine influence the figures measured comming out of the machine.
perhaps with some of these machines, the fine dust or a large portion of, has already blown thru the filter, leaving predominantly coarser material to be measured. Perhaps reality is worse than the instruments indicate.

The minimally dust loaded air going into the DCs churns up a dust storm inside the bags so what comes out of the filters is a mix of the dust in the incoming air plus the dust already in the bag, plus DC generated dust. The size of the particles inside the DC may be influenced by factors such as time, weather, initial particle size, flow/churn rates and type of material etc. All I am able to do is measure an OUT/IN ratio and while there is clearly a lot happening in between it is a semi-practical snapshot of what dust levels are being generated. I would expect things might change if different dust loads were applied but measuring the particle distribution/concentration of say the dust generated by a sander or table saw heading into a DC involves sticking the particle detector I have into a duct which is a sure fire way to damage it as it cannot handle this type of a dust load. There are particle detectors that can do this but I do not have access to one of these.

It occurs to me. the only difinitave way to test these filters is with "known dust".......where do we get that from?

A source that produces particles of a know size range is available - that's how HEPA filters are tested.
The material used was DOP (Di-Octyl Phthalate) and even though it is no longer used (carcinogenic) the name has stuck.
I would prefer to work with known dust like MDF but I cannot work with high concentrations or it will stuff up the detector.

No sorry but some people are too lazy to think or are they just plain dumb or do they just not care.

Why would anybody go a buy pleated cartrige filter, that probably cost as much as the dust extractor its self, the primary purpose being that it is a better filter than a cloth bag and simpy leave the coth bag fitted to the bottom of the dust extractor.

As I walk about in the world I just can't believe people can be that stupid, but time and time again I see that people fail in very simple concepts of engineering and logic.

It has to be that they never actually thaught about it.

More importantly, the person who sold them the pleated cartrige filter only did half the job.

"Yeh mate...remember when you fit this filter you have to replace the bottom bag with plastic (there are 5 in the box) or all the crap will keep comming thu the cloth bag and you might as well have ya money up against a wall.

No instruments required just a simple logical explanation.

cheers

I have a couple questions.

Do more filters on a dust colector improve the filtration? My logic being that the more filters, larger area for the air to move through, reduces the pressure differential across the filter which would reduce the fine particles being pushed through. Four filters better than two, 6 filters better that 4 etc., type of thing. Is my logic wrong? Is there a point of diminishing returns

All the industrial installations that I have looked at have the air moving from the outside of the cartridge towards the middle. Why do home woodworkers make their installations work in the opposite direction? I know the manufacturers just slap a filter on in place of a bag for convenience but don't understand why we do it opposite to industry, especially if we use industrial filters.

Thanks for your opinions.
Pete

I'd say in most cases they are not dumb, they haven't really stopped to think about it.

Originally Posted by soundman

No instruments required just a simple logical explanation.

Now who's being optimistic? I don't see logic winning too many people over anywhere, including this forum. The average joe sticks with what they can see, anecdote, what their mates said, and evidence to support long held beliefs. In many cases not even the hard facts / numbers work - look at politicians and the general voter.

Originally Posted by QC Inspector

I have a couple questions.
Do more filters on a dust colector improve the filtration? My logic being that the more filters, larger area for the air to move through, reduces the pressure differential across the filter which would reduce the fine particles being pushed through. Four filters better than two, 6 filters better that 4 etc., type of thing. Is my logic wrong? Is there a point of diminishing returns

It depends what you mean by filtration
More bags or pleated filters that increase the surface area and reduce the pressure drop which will increase the flow rate which will pick up more particles at source but I'm not convinced it will ultimately reduce the proportion of fine particles that pass through the filter. I can do a test to check this out and I will add it to the list.

All the industrial installations that I have looked at have the air moving from the outside of the cartridge towards the middle. Why do home woodworkers make their installations work in the opposite direction? I know the manufacturers just slap a filter on in place of a bag for convenience but don't understand why we do it opposite to industry, especially if we use industrial filters.

I don't think there is any difference, one is just a simplified lower cost topological inversion of the other
I think it is just for ease of DC construction and containment of the dust. To do thing

Hi Bob,
If you happen to test a Nilfisk Alto Attix Xtreme Clean dust extractor in your travels I'd be glad to hear about the results thanks