Portable Dust Extractors archive

Thursday 23 September 2010

Alan Holtham on why you need efficient dust extraction and the effectiveness of the two collection systems

Gallery

We will happily spend hundreds of pounds on some new tool or machine, but carry on working in a cloud of dust because we are reluctant to spend a much smaller amount on dust extraction.

Dust is the really fine stuff with a particle size measured in microns, and although our respiratory system has developed a number of strategies for dealing with larger particles, there is nothing to stop the really fine ones, and it is these that gradually accumulate in your lungs. This accumulation may not result in any immediate symptoms, but by the time they do finally manifest themselves it is often too late and the damage has already been done.

There are other dangers as well. Sometimes you can work with a particular timber for years and never experience any reaction until suddenly the critical sensitising dose is reached and you can then never use that species again. Typical examples with bad reputations are yew, red cedar, Santos rosewood and ebony. Also, spores from some spalted timbers are often more harmful than the dust itself. Do not work timbers that are at all doubtful.

Fire risk

The other main risk of dust in the workshop is that of fire. A concentration of about 100 grams of dust per cubic metre of air is sufficient to form an explosive mixture. All you need is one spark to set it off and it is time to plan the new workshop, assuming you are still around.

This fine dust settles out on any flat surface, and even clings to the walls. Lift a tin off a dusty high shelf and you could end up inhaling a supply of one month in one dose.

Proper dust collection systems installed at source are the first line of defence for a big workshop, see my article on plumbed-in extraction. Smaller workshops may only need some form of portable extractor, particularly if you can back this up with appropriate personal protection such as a dust mask or air-fed helmet. For real protection install an air cleaner as well to minimise the airborne haze of fine dust.

Sadly, there is no one machine that will cater for all the various dust situations, but one of the most useful starting points is a good-quality portable dust extractor. These come in two distinct types, high volume-low pressure, known as HVLP, and high pressure-low volume, known as HPLV.

HVLP extractor principles

The dust and shavings of HVLP extractors are sucked through the impeller and then fall into the lower bag, the air being exhausted through the top filter bag, collecting some of the fine dust on the way.

However, the bag can only filter out particles down to about 20 microns, depending on the type of cloth it is made from, anything smaller than this being blown back through the bag and into the workshop. Unfortunately it is just this size of dust that is most dangerous.

Because they shift huge volumes of air at low pressure they are very efficient at removing bulk waste such as that from planers, hence their reclassification as chip collectors. Their fine filtration efficiency can be improved somewhat by fitting a filter cartridge instead of the bag.

HPLV extractor principles

HPLV extractors move less air at much higher pressures. Operating more like a standard vacuum cleaner, they are better adapted for continuous use and have a much bigger waste storage capacity than a domestic cleaner.

They can usually collect dust down to 0.5 microns and are better suited for enclosed areas where the air is constantly recycled as in the home workshop.

The most portable are the canister type with 100mm hose or vacuum cleaner type with small-bore hose, featuring a powerful through-flow motor surrounded by a cardboard filter which is then covered by a paper filter bag.

This gives two levels of filtration, the incoming air being exhausted out through a grille in the top of the noise-absorbing acoustic hood. As filtration efficiency varies significantly between manufacturers, check this feature when comparing specifications.

The hose is connected to the machine at the inlet boss, the standard size being 100mm. For use with power tools there is usually some form of adapter to reduce down to 32mm, so, incidentally, increasing suction.

The other advantage of using this type of extractor with power tools is that some models have auto switching. Your power tool is plugged into the socket on the extractor itself, so when you switch the tool on, the extractor kicks in a split second later. When you switch off, the extractor runs on for a few seconds to clear the hoses and then switches itself off.

Also, check carefully the capacity of the power rating for the extractor outlet as some are quite small and may not allow you to use heavy-duty tools. You need a capacity of at least 2000W to cope with most heavy-duty routers and saws.

Dust collection

The dust is collected either into a plastic sack or a rigid drum. Because the vacuum is so efficient the tendency is for a bag to collapse inwards under pressure, hence a mesh cage to maintain the shape. However, when you switch off the dust falls to the bottom and makes more space.

Expect a capacity of about 60 litres in a bag of this size, but do not compare this with an HVLP collector as the vacuum of the high-pressure systems tends to pack the dust down much more tightly. I have seen figures quoted of up to four times more capacity than an equivalent bag in a low-pressure system.

Rigid waste container

While rigid waste containers may look cavernous, remember that as soon as you fit the motor unit back in place much of the apparent space is lost.

Have a good look inside the container at the area around the inlet. This often has a baffle to control the flow of the waste, as a small lump of wood or a nail sucked into the extractor can quite easily puncture the filters.

It may become choked by small offcuts or bits of sandpaper so clean it out if the efficiency falls off.

Tool dust bags

Many tools are fitted with a dust bag as standard, but in reality these are rarely effective particularly with regard to fine dust. The only answer is to couple the tool directly to the vacuum extractor using an integrated system.

Any diameter differences are easily overcome by fitting a simple tapered adapter that can be cut to suit.

Pressure cuff

With a strong vacuum the end of the pipe can suck itself tight onto the floor, either bursting the bag or pulling a drum machine over, so if you intend to sweep the floor with it, do use a pressure-releasing cuff with an adjustable inlet hole.

Wet-and-dry

A wet-and-dry function allows the machine to suck up liquid spills too but an internal float mechanism is needed to prevent damage to the motor if the waste container gets too full.

Other considerations

The HPLV systems with their low airflow actually have very little suck until connected to the machine, so with a lathe where there is no real connection point, get as close as possible to the source of dust. I use a large crocodile clip on the end of the hose and just clip it wherever the dust is.

Drum extractors

Using light, portable collectors on a high-volume waste producer soon fills the bag. The types that operate into a drum are easier to deal with, as there is then no danger of split bags, and the drum is simple to empty. Really powerful, they are harder to move around, particularly when half full, so check if a wheel kit is available.

The ultimate is the 2-motor wall-mounted version that uses plastic sacks for collection. High levels of filtration along with around 200 litres of capacity bring it into the realms of the semi-industrial user.

Hoses and tools

For comfortable working, particularly when attached to power tools, the hose must be as flexible as possible with minimal ribbing because this always catches on the edge of the bench or the work.

A variety of different tubes and nozzles is very handy for general workshop cleaning and the more conventional floor brush is essential.

Wheels

For stability, look for five or six large-diameter castors on the container. A rubber bumper round the base of the container will protect both it and your machine as you pull it around the workshop.

Power lead

Anything that discourages you from using the extractor should be avoided and if you have to keep unplugging and then plugging in again as you move around the workshop the natural tendency is always not to bother, so find an extractor with a lead that will easily stretch the length of your workshop and still have plenty of slack left so that you do not trip over a taut cable.

Locks

Another feature I have noted on some extractors is that the locks that hold the motor unit onto the canister stick out quite prominently, tending to foul as you drag the extractor around.

Bigger or smaller

Much heavier-duty workshop vacuums are available which as well as having a bigger waste capacity and more powerful motors are also more easily moved around having larger diameter wheels and proper manoeuvring handles.

At the other end of the scale are light-duty cordless models which are more portable than their mains equivalent so good for site work, but less powerful.


Woodworkers Institute

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Alan Holtham , Dust Extraction , Shop Talk , HVLP , HPLV , chips