Questions on Dust Extraction

[Arron]

Hi guys. I recently bought a 2 hp dust extractor and have a couple of questions about dust extraction. The first one is that I am curious about putting a separator of some sort in front. I expect this will be something like a large plastic garbage bin with a couple of baffles in it. My intention is to stop whatever large pieces I can getting into the bag - especially as there appears to be no easy way to empty the bag. Has anyone done this and can they pass on any information about what worked and what didnt ? I have read that this will reduce the suction somewhat, was that the case ?

Anyway, when I got the thing home from Carbatec I started it up and sucked some dust - then I touched the bag and was not altogether surprised to see a cloud of dust ensue. The dust was of a quite visible size and was coming out from inside the bag, so I guess what I was told about the things having a filter size of 3 microns really is nonsense. My garage is my workshop - its under our house, and I am wondering about siteing the dust extractor on the other side of the garage wall (in the general under-house area, which would need digging out of some clay). Presumably the very fine dust would be extracted out of the garage into the under-house area, flow out of the bag, then be limited in its ability to seep back. Is there a problem with this - some sort of fire risk perhaps.?

thanks
Arron

[Eastie]

It is most preferable to site the dust extractor in a location where there is abundant natural air flow and ventilation. If placed under the house, I expect you will have problems down the track with vents under the house clogging up with dust and cobwebs. As for the fire risk, unless you’ve got a naked flame (pilot lite) under the house the risk of fire/explosion is low. Other considerations include ducted heating/cooling ducts as these often have holes or gaps in joints where dust can get in.
It could be done, but I’d consider other options first including a length of flexible duct so you can put it outside when in use.

As for dust leaking out, this is normal. I’ve heard that after a while less dust escapes as dust already on the walls of the filter bag acts as a filter in itself. After some years of undertaking dust sampling in workplaces I consider this to be simplistic thinking and nonsense (with dry membrane filtration).

Best wishes,
Mark

[Wayne Davy]

OR you could look at building a Cyclone. That 2hp blower is a good base for one (its the size I used).

[Arron]

Wayne, I'm waiting for you pioneers to get all the problems with building home-made cyclones sorted out before I give it a go. Maybe in a year or two...

Mark, thanks for your response. I did consider putting it outside, either temporarily or permanently as we have wide eaves which would give it some shelter from the weather. My concern is that we are close to our neighbours. I dont want to be pumping stuff outside to their detriment just to preserve my own health. Do you think that is an issue, or is it a case that once the very fine dust is outside in the big wide world it is no great danger ?

thanks for the response
Arron

[Wayne Davy]

Arron,

No problems in building one - check out my site for details
http://members.optusnet.com.au/~wayne_davy/

Also, on having the Bag DC outside, it probably would not be much of a problem for your neighbours as the fine dust would disipate in the outside air. That is unless their house is right on the boundary and your D/C would be right next to them - that might be a worry.

I would add just one thing though, if this puts the D/C a fair way from your tools, you will be looking at a large drop in suction particularly if you use flex hose. Look at using PVC from the DC to your shop and minimse any flex used. This will help a lot.

Good luck

[Eastie]

There are three old principles that apply to substances and their effects on health:
[list=1]
The dose makes the poison
Even strong poisons are harmless if the dose is low enough
The higher the dose, the stronger the poison
[/list=1]

This has always been a dubious proposition because a "safe" dose for one person is not necessarily safe for another as people vary greatly in their tendencies toward illness and disease.

Timber dust has generally been classified as carcinogenic. The risk to us is a combination of toxicity and exposure duration – or in other words the dose.
Simply put, what Wayne has pointed out is correct, the dust should be adequately dissipated an thus present a negligible risk, which must be looked at in terms of other risks we take from day to day.

Mark

[Dan]

Is the air after a cyclone clean enough to be exhausted to the outside world unfiltered ? I was thinking along the lines of a 6" stack straight through the roof or through the wall then up the side of the shed to just above roof height.

Not planning on building one yet but may consider it further down the track.

[Wayne Davy]

Dan,

If the cyclone is designed and built correctly (ie. mainly correct top drum to cone length) then the outlet air is quite clean. You would not want to stand in front of it and breath in but I believe it is fine to vent outside, as the little bit of fine dust remaining would dissipate.

My Cyclone actually vents directly out the side of the building. No neighbours on that side of the house (empty, derelict house next door) and there are no windows on our house in that spot so I am lucky I guess.

Just a point though. Running a lot of duct even on the outlet side will affect the suction as it will add to the resistance. You need to keep all pipe to the minimum length possible and nice gentle bends to maintain the max suction at your tools.