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  1. #76
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    Can I spoil your analysis with a hand-waving sort of vaguery?

    Ever since I was young I can remember using a vacuum in my room - probably annually, when the books reached the level of the bed and either it was time to study, or else exams were over - and I am/was sensitive to dust (mites I think). I'd get a runny nose and red eyes, and felt that the vacuum was definitely sending dust out into the air. I used to tie a diagonally folded handkerchief over my nose/mouth, which would help a little.

    About ten years ago - very definitely not like us - we bought a Kirby vacuum after an in-house demo. $3000+ and we bought it because it blasted our rug of dog hair ... and still does.

    My question/point is this ... whenever I have used that vacuum to really get into a neglected room - the air in the room has felt (to me) appreciably cleaner and I haven't had that reaction. Literally breath in and smile.

    I don't suppose it is performing better than your vacuum ... we only use the genuine Kirby bags but there isn't any other filter ... can you comment on what you think is happening?

    I looked up dust-mites and get 0.4mm long = 400 micron, so maybe it is all a size thing?

    I really really appreciate the vac we have - plus the fact it promises to have the working-life of a table saw. You guys have mentioned invisible dust/particles. Maybe the human perception of (much?) larger particles being removed is a strongly positive one, and so that is what marketing and engineering of products has benchmarked against.

    Customer feedback vs particle detector ... or Marketing over Engineering.

    The creation of smaller un-noticed particles would (by definition) be a non-issue until someone told you (a) they were being generated and (b) that it was undesirable.

    Cheers,
    Paul

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  3. #77
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    Thanks for your thoughts Paul and SM.

    Re: Seal around a vacuum cleaner bag.
    Unlike a DC I don't think the bag to VC seal on a VC matters as much as that area is under negative pressure so dust goes into the VC and on a two stage VC that dust will be trapped by the HEPA (like) filter.

    I agree about the bypass motor being a much better system for cooling the motor, except they then become add-on dust mincers and turn larger dust into finer dust. I haven't posted on this but I have measured the dust coming from the bypass motor cooling airflow on several $1000+ vacuum cleaners and they show a 2 to 3 fold increase in finer dust output - there is no discernible change to larger particles but it only takes a few large particles to make zillions of little ones. A better system puts a(nother) HEPA after the motor so all the captured and minced dust is at least captured by the HEPA.

    All these problems continually point to why all of the extraction machinery should where possible be located outside a work area.

    RE: Dust mites
    Most bugs are relatively large but of course they die and break up into much smaller pieces and these can cause as much of a problem as the full size critters. The same thing happens with skin, carpet and cloth fibres.

    One thing I have been reading up on is "charged dust". This, together with what soundman refers to as moist dust creates a wide range of dust clumps. These mechanisms can turn the less dangerous <0.3 micron dust into clumps of >0.3 microns.

    I can indirectly observe moist dust if it has not rained for a while and then the humidity rises. Superfine (<0.3 micron) dust in the air acts as a nucleating site for water molecules to condense onto (this is basic rain making) which makes the fine dust sticky and it then picks up other fine dust and more water. The observable is the fine dust levels increase above the usual background. Then when it rains, this clears a substantial amount of the moist dust plus other dust from the air. (please don't raise this as another dust clearing mechanism; a) as Soundmand says this creates a dirty water disposal problem and b) moist environments are not very compatible with woodworking tools.

    The charging effect is more complicated. Charging apparently takes place via a number of mechanisms commencing at the dust forming site. On drier timber surfaces charging can occur during processes like sanding when dust is torn away from wood in the same way that sticky tape torn away from a surface charges the tape. Additional charge is added to dust through friction via collision with other dust within a high speed air stream. Charging has minimal impact on chips and bigger dust particles but it does contribute to clumping of fine from super fine dust. The swirling action of DCs and cyclones can charge and through collisions break up larger particles into smaller ones. On industrial scale DCs electrostatic precipitation is employed to advantage to assist in capturing these. I hope to be testing one of these units in a few weeks time.

    So back to Paul's post about the air feeling good after vacuuming. I'd like to see a double blind test on this, but charging of the dust by vacuuming could have something to do with it - ie the vacuum cleaner does nothing more than charge the dust that for whatever reason feels better than the uncharged dust.

    RE: The creation of smaller un-noticed particles would (by definition) be a non-issue until someone told you (a) they were being generated and (b) that it was undesirable.
    I agree a certain amount of this is inevitable and only a double blind test would determine if this was the case.

    Like I have constantly stated, the riskiest thing most WWW do is drive to the hardware store.

  4. #78
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    Not much info on the bag ...

    kirby bag.jpg ... hmmm ...

  5. #79
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    The blurb looks like those 85dB rated muffs to me.
    99.97% of common household ....... means very little, could be 99.97% of 25 microns or bigger.

    If I had nothing better to do I would ask you If I could measure it's efficiency but I am flat out trying to do the tests I am doing.
    Maybe if some opportune path crossing time occurs?

    Quote Originally Posted by pmcgee View Post
    Not much info on the bag ...
    ...

  6. #80
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    Default Follow up on HEPA filtered Vac.

    Today I replaced the HEPA filter on the European VC I have been messing with lately.
    The flow rate increased from 85 to 93 cfm but as I expected there was no improvement in the particle counts.

    The filter box says the filter is an H13 so thats 99.995% DOP (That's a >0.3 micron rating)
    It also says max flow is 75 cfm? - presumably that allows for a bit of filter seasoning

  7. #81
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    Quote Originally Posted by BobL View Post
    The blurb looks like those 85dB rated muffs to me.
    99.97% of common household ....... means very little, could be 99.97% of 25 microns or bigger.

    If I had nothing better to do I would ask you If I could measure it's efficiency but I am flat out trying to do the tests I am doing.
    Maybe if some opportune path crossing time occurs?
    Sure Bob - any time - I'm going nowhere.

    ... hmmm ... that sounded kinda depressing ..

    Paul

  8. #82
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    Also Bob - I forgot these -

    Assuming a near-perfect filtering solution in terms of particle capture, would there be practical implications for filter life vs expense?

    That is, would a reasonable costing solution clog up so fast people wouldn't stick with it?

    or would the extra particles being captured be so small that the effect on filter life wasn't so bad?

    A cyclone wouldn't play any part at these particle sizes?
    Something couldn't go into a DC to regularize the flow to decrease the 'wash cycling'?

    Thanks,
    Paul

  9. #83
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    Quote Originally Posted by pmcgee View Post
    Also Bob - I forgot these -
    Assuming a near-perfect filtering solution in terms of particle capture, would there be practical implications for filter life vs expense?
    Unlike the way I/we have treated our home HEPA vacuum cleaner my experience at work is that high capacity HEPA filters can be easily protected with high capacity low resistance pre-filtering and regular maintenance. We regularly have achieved 7+ year lives from HEPAs that take air direct from the outside (ie a dirty car park), pre filtering it and then HEPA-izing it. Wood work dust loads would be a couple of orders of magnitude above this but this is easily handled using a cyclone as a prefilter. I would expect a cyclone protected HEPA to last for a decade.

    But unless one is operating on a large scale or cannot vent the invisible dust outside then neither cyclones or HEPA filtering are required.

    That is, would a reasonable costing solution clog up so fast people wouldn't stick with it?
    or would the extra particles being captured be so small that the effect on filter life wasn't so bad?
    The key to keeping costs low is pre filtering.

    A cyclone wouldn't play any part at these particle sizes?
    see above.

    Something couldn't go into a DC to regularize the flow to decrease the 'wash cycling'?
    Not sure what you mean by this.

  10. #84
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    Re the bypass motors being dust mincers......no doubt.

    But in the vast majority of domestic and industrial vaks, there is no filtration after the motor, the motor will therfore act as a dust mincer any way.

    A very real source of fine particles IS the comutator and brushes of the universal motor used in almost all portable vak machines.

    Having worked on machines that have enclosed universal motors, I can tell you they produce significant quantities of fine material as the brushes and comutator wear.....its possible less mincing of dust and more making of it.

    One machine I worked on in my apprenticship, it was common for the motors to be ruled unfit, because of low insulation resistance before the brushes where more than half worn...this was due to the carbon dust deposited inside the sealed case.
    In fact the majority of motor fauts where not failures but insualtion resistance issues.

    Most power tools and appliances with universal motors this does not happen because the cooling air takes this fine carbon dust out of the machine and spreads it around our houses and workshops as...you guessed it....."invisable dust".

    Charged particles, clumping and electrostatic filters.

    As i mentioned earlier, seems to me that most air filtration has gone back to filters more or less based on sieves, and we don't seem to be seeing some of the other technologies we saw in the past.

    I can remember there was a lot done with air ionisation and electrostatic filters back in the 80's......like water bassed air scrubbers and other things we seem to hear nothing about electrostatics and ionisation these days.

    I remember seeing domestic and industrial negative ion generators for sale and in use....it was well known that if you put a negative ion generator near a wall, the wall would soon be covered in fine filth that was very hard to get off......this was "Invisable Dust" that got charged and stuck to any uncharge surface it came near.

    Electrostatic filtration worked in a similar fashon, but combined a filter with an ioniser to achieve very fine particle capture.


    As far as water scrubbers and introducing humidity into the air.......large industrial evaporative coolers are getting very popular in large industrail and even commercial buildings.

    Why can these machines be modified to be watter bassed air scrubbers.....maybe a reduction in the air flow, and increase in water flow and slight changes to the mesh or exchange eliment that already looks like a filter.

    Then there is the notion of chemical enhancement to filtration...almost every large commercial building pumps deodorant, disinfectant or fragrence into their airconditioning.
    Surely there is a harmless product that could be introduced near filtration inlets that would promote clumping, reduce dust holding and enhance filtration.

    cheers
    Any thing with sharp teeth eats meat.
    Most powertools have sharp teeth.
    People are made of meat.
    Abrasives can be just as dangerous as a blade.....and 10 times more painfull.

  11. #85
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    Default More testing

    I tested the efficiencies in another shed during the week.
    The shed contained a wide range of machines, BS, TS, Lathe, Thicknesser, Belt sander, SCMS, a VC and 2 internal and one external DCs.
    There was some dust and chips on the floor.
    A large full width roller door opened onto a concrete paved area which was also used for WW.

    No real surprises but a couple of interesting measurements, including some involving the use of an arbortech cutter/shaper and also using a table saw.

    The graph below refers to two conventional DCs
    DC1 is a 2HP well used DC with top and botton cloth bags located outside the shed although a little too close to the front door for the location to be as effective as it might be .
    The bottom bag had been repaired in several places with what looked like adhesive patches - nevertheless it had no obvious leaks and looked reasonably clean.
    It was about to be emptied but I asked for it not to be emptied

    DC2 is an internally located 1HP DC with a Needlefelt bag and that was performing about where it should be.

    Want your DC checked for invisible dust?-dc1and2-jpg

    The interesting observation is the significant difference between the performance of the top and bottom bags of DC1. My interpretation of this is that sawdust has swirled around so much in the bottom bag that it has worn away some of the calico and reduced it's efficiency. So it's a good thing this bag is located outside the shed.

    I also measured the dust levels inside the shed at various times during my visit.
    When I arrived a bandsaw had just been briefly used and in the middle of the shed it was <0.15 mg/m^3.
    At various other points in the shed it ranged from 0.04 to 0.20 mg/m^3
    One minute after using a TS for about 5 minutes it was <0.23 mg/m^3 in the middle of the shed
    Even though there was some dust and chips on the floor and some machines, depending whose OHS limits one decides to use, these measurements suggest their 2HP DC and big roller door ventilation is doing a fair job, but of course if more than a couple of machines are in use or any one machine is used for an extensive period then I can see see the levels easily exceeding even the most lax OHS levels.

    I also calculated the total wood dust escaping from DC1 (the DC located outside) while timber was being cut with the table saw.
    The output was only 3 mg of wood dust per minute. If this "rather ordinary DC" was located inside the shed, theoretically it would take ~20 minutes of continuous cutting to reach the OHS limit of 1 mg/m^3.
    Of course this assumes the DC collects 100% of the dust being produced at source (ie most unlikely) and the dust spreads uniformly through out the shed (it doesn't - see measurement above). I would also expect the outcome to be different if a finer dust producing activity was involved. However, it does suggest that collection efficiency is as least as important as location.

    The graph below shows the efficiency for a single cloth bag 1HP DC and a budget price range VC connected to a home made chip collector.
    Both are pumping out between 100 to 200% more fine dust than they were taking in. Once again either they are mincing dust or they already contain a lot of dust that they are pumping back out.
    This is the worst single bag DC I have measured, others have been above 90% efficiency probably perhaps because they were well seasoned.

    Want your DC checked for invisible dust?-dc3andvc-jpg
    The most interesting measurement I made was of an arbortech carver being used outside with a slight breeze blowing. The dust levels near the operator was around 3 mg/m^3 after only about a minute of operation. This suggests that a mask should definitely be worn even when using one of these tools outside.

    So all in all an interesting visit.
    Attached Images Attached Images

  12. #86
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    Default Another face mask

    Back in post #55 I posted some data on face masks. Earlier this week while testing some DCs I was given a Medical Mask to test and here is the results (Orange line) in relation to the other masks I tested.

    Want your DC checked for invisible dust?-masks2-jpg

    It looks like that medical mask is as good as the P2 Type mask for the bigger particles and half way between P1 and P2 for the smaller stuff. From what I can see about the medical mask it is not as contoured a fit as the conical style face masks that are more commonly used for WW but they are certainly better filters than the Nuisance or No brand masks. I'm not sure what they cost but it seems like they come in boxes of 20? or more so unit pricing might be quite low.

    If anyone wants to know the name of the specific mask you can PM me.
    Attached Images Attached Images

  13. #87
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    Quote Originally Posted by BobL View Post
    I tested the efficiencies in another shed during the week.

    The interesting observation is the significant difference between the performance of the top and bottom bags of DC1. My interpretation of this is that sawdust has swirled around so much in the bottom bag that it has worn away some of the calico and reduced it's efficiency. So it's a good thing this bag is located outside the shed.

    So all in all an interesting visit.
    Bob,

    If my memory serves me correctly, the two bags have been swapped about, because the one that was on the bottom was starting to tear near the spring securing clip from the weekly emptying.

    Also the the bag on the bottom has a small hole near the bottom of the bag, around on the inaccessible back side, but because it was about half full no air was escaping through it.
    Arie.

  14. #88
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    Quote Originally Posted by Breezy View Post
    Bob,

    If my memory serves me correctly, the two bags have been swapped about, because the one that was on the bottom was starting to tear near the spring securing clip from the weekly emptying.

    Also the the bag on the bottom has a small hole near the bottom of the bag, around on the inaccessible back side, but because it was about half full no air was escaping through it.
    Thanks Breezy. That small hole in the bottom bag will easily explain the higher result for the bottom bag. I scanned all 3 of the accessible sides and could not find a specific leak so I attributed to bag thinning.
    I hope you found the info useful.

  15. #89
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    Default More VC testing

    During the week I tested another high end HEPA filtered VC.
    The VC was in excellent condition and looked like it had been very well looked after.

    The results for the air exiting the HEPA showed nothing unusual (all >99% efficiency) when used with
    - a used dust collection bag
    - a new dust collection bag
    - a ROS sander with 240 grit paper.
    This shows the HEPA is in good working order and doing its job.

    For the first time I also measured the dust levels in the air in the immediate vicinity of the sander after the 2 minutes of sanding, the results of which are shown below.

    The negative % decrease (ie increase) of the particles <1 micron is easy to explain by saying that the sander doesn't catch the fines as easily as it catches the coarser particles.
    However, the positive % decrease of the particles >1 micron is intriguing.
    I cannot see how the sander can preferentially scavenge the coarse particles out of the shed air.
    If anything the finer particles, which are more mobile, should be preferentially scavenged.




    One complication when testing VCs is that the typical hoses are not very long and if the test is performed inside a restricted space (eg a small shed) and the air intake may not far enough away from where the air is exhausted from the VC back into the shed. The pressure gradient will also drive the movement of the exhausted air from the VC to the air intake.
    The big question is where do all the extra fine particles come from?

    One source is from the motor cooling circuit as shown in this graph with the motor putting out between 1.28 and 50 times more dust than is in the back ground. This seems to be a common issue with these and many other VCs.



    My explanation is that the shed air after sanding is a mix of HEPA filtered air (with low levels of all particle sizes) and the dust coming from the motor.
    I would be interested in hearing any other explanations.
    Attached Images Attached Images

  16. #90
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    I postulate that the thing with the ROS, is it does not scavenge particles out of the air at all.
    It extraction of material that is under the disk will be nearly 100%, the waste material generated at the edge of the disk may escape, the coarse material is likley to stay on te work and be picked up in the next oscilation where the finer material is more likley to be come airborne.

    It would be very interesting As I have said before to examine the changes with different grit sizes..it is my view that the collection efficiency of ROS may become less as the grit size is reduced because there is less air flow between the grains of grit.

    I also expect to see more fine material generated by finer grit sizes.

    so the finer the grit size the more fines generated and the less efficient the capture.


    Still far more efficient than a belt sander or a conventional orbital.

    cheers
    Any thing with sharp teeth eats meat.
    Most powertools have sharp teeth.
    People are made of meat.
    Abrasives can be just as dangerous as a blade.....and 10 times more painfull.

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