Trupro 2HP Dust Collector

I’ve referred to my new dust collector (or dust extractor, depending on your terminology) in a number of posts, but noticed I have been rather lax in not discussing the machine itself.

Where it comes to dust collection, bigger is definitely better. Oh, and while we are on the topic of bigger, let’s quickly touch on what we are trying to collect.  In a workshop, sawdust takes all sorts of forms – and even the term sawdust is misleading – the saw is only one of a phenomenal range of machines and tools that can turn wood into a waste product that we want to collect, store and dispose of.

The waste can be fine dust through to heavy wood shavings from a handplane, and everything in between.  Some are easier to collect than others!  Fine dust is nasty for the lungs, and relatively easy to collect, so long as it is actively done as the dust is generated.  It is very light, and is picked up by pretty much any type of extractor.

The heaviest stuff (shavings from turning, or from handplanes), is almost easier to get with a broom……or a shovel.

In between, we have the jointer/planer and planer/thicknessers.  These produce a wide range of results, at the same time, and huge quantities of it so that is what is really desirable to pull away with an extractor.  It can be quite long and thin, and can easily block a pipe when air flow is insufficient.

So onto the dust collector itself.  Sourced from the Woodworking Warehouse, value is $A1175.

Trupro Dust Collector

Trupro Dust Collector

(yes, it is a photo I’ve used a couple of times already, if it looks rather familiar).

The collector has 2 main components – the motor and extraction fan, and the collector itself. The motor, as mentioned is 2HP, but boy does it draw a current on startup!  It tripped out the breaker on a powerboard every attempt to start it, so have had to dedicate a primary power point to the machine (still 10A), and that has solved any startup issues.

The motor drives a rudimentary centrifugal fan.  This is not uncommon in dust extractors, the clearances cannot afford to be too tight, or the parts too fine due to the bulk of the particulate that the fan is expected to cope with.  Also, given that it is sucking from a workshop there are all sorts of other bits and pieces that can also be picked up and fly through the tubes into the fan blades.

The motor is not particularly noisy in its own right (it is an induction motor), the noise is certainly from the air flow.  I’m not sure if the design could be improved to smooth out the airflow to reduce the generated noise.  However, it can’t be a particular criticism of this unit, because it is a very common design. The overall quality of the unit is apparent in the build of the 60kg unit.

Airflow rates: The machine is rated at 1200 cfm (2040 m3/hr).  This is around the median for a 2HP machine.  If you put it in a different vein, the total shed volume is 80 m3, so in theory this machine could empty the shed 25 times in an hour.

In practice, using an airflow meter, I’ve estimated the actual performance of the machine in 3 orientations:

As supplied with the twin 4″ connection points, both open.  Flow rate 28 m/s

As supplied, with one 4″ connection point covered with the supplied cover. Flow rate 45 m/s

With the twin connector points removed revealing the 6″ entrance. Flow rate 33 m/s

These figures are much higher than they should be, so our guess is that my assumption that the measure of flow speed being the average across the range of speeds experienced (between the edge of the pipe and the centre) doesn’t hold true, and it is really picking up the peak speed only.  I’ve removed my conversions, because the ones in the comments make a lot more sense than what I came up with!!

The other side of the DC is the collection aspect.  A basic form of collector uses a dust bag top and bottom.  These need to be air permeable, as the air being pumped in has to have somewhere to go – through the sides of the bags filtering out the entrained dust.

This unit uses a tough plastic dust collection bag on the bottom, and a spun-bound polyester pleated filter on the top.  This is where the air escapes the system.  This pleated filter can filter out particles as small as 1 micron.

You’d (correctly) imagine that a pleated filter would fill with fine dust, and the filters are not particularly cheap.  There is a way to clean them, or at least knock a lot of the dust loose so it falls into the lower bag.  Built into the pleated filter is a 3 paddle cleaner, and by rotating the top handle through 120 degrees results in the paddles beating every pleat, releasing the trapped dust.

Pleated Filter Cleaning Paddles

Pleated Filter Cleaning Paddles

This is a photo up into the top filter.  You can see about 1/2 the pleats, and 2 of the rubber tipped cleaning paddles.

So an effective dust collector / dust extractor and one that you can use in your main shop because of the 1 micron filtering of the air being exhausted.  There is quite a bit of noise generated by the unit, so either you wouldn’t want it running until needed, or some form of noise block wall shielding it from the rest of the shop.

Overall, this is a solid machine that performs.  I have some problem with the intakes getting blocked with large particles, such as planing shavings, and the long fibres formed with the thicknesser, but this can be addressed with either an added 1st stage cyclonic collection, or perhaps by removing the coarse grate the is across each port (to protect the blades). Otherwise, it has plenty of suck, and that is what counts in the end!

5 Responses

  1. 28m/s through 2 x 4″ ducts = 28 * (0.1)^2 * Pi * 2
    = 1.7m3/s

    1 cubic foot = (0.0254 * 12)^3 = 0.0283m3

    Therefore 1.7m3/s = 1.7/0.0283cfs
    = ~60cfs
    = 3600cfm?

    Assumes constant flow across the width of the ducting, which is far from a given.

    Single 4″:
    45 * (0.1)^2 * Pi = 1.41m3/s
    = ~50cfs
    = 3000cfm

    6″ outlet:
    33 * (0.1)^2 * Pi = 1.04m3/s
    = 36.6cfs
    = 2200 cfm

    As a check of my conversion:

    1200cfm = 1200 * 0.0283 * 60 = 2037.6m3/h.

    What happens if you measure the flow rate at the edge of the duct?

  2. 28m/s through 2×4″ ducts:
    4″ = 0.1m
    area = 3.14159 * (0.1/2)^2 = 7.85 e-3 m^2
    volume = 28 * 7.85e-3 * 2= 0.44m^3/s = 1584m^3/h
    (or roughly 78% or rated).

    45m/s through 1×4″ duct:
    45 * 7.85e-3 = 0.35m/s = 1271m^3/h

    33m/s through 1×6″ duct:
    area = 3.14159 * (0.15/2)^2 = 1.77e-2 m^2
    volume = 33 * 1.77e-2 = 0.58m^3/s = 2099 m^3/h

    That of course assumes even airflow across the entire duct, which isn’t very realistic. I’m sure you could get a derating factor from one of the American rags (eg. FWW). It is also why the 6″ number is higher than the spec (the spec will be with the 4″ adaptors off because the highest number they get will always be with the largest opening).

    My understanding is that a more useful measure is the static pressure they can develop (ie. plug the hole and measure the vacuum generated). This is harder the relate to real life performance though, and would only be useful for comparing similar machines.

  3. Thanks guys – appreciate the input. I shouldn’t try to do calcs after midnight (and rely too much on the conversion programs on my iPhone!)

    I’ve removed my conversions from the article, because these look to make a lot more sense!

  4. Ahh you idiot Juffles. Pi * R ^2, not Pi * D ^2. Clearly I shouldn’t try to do elementary trig any where near midnight. 🙂

  5. Rats – I have gotten to the point that I have not only dragged one of my old text books out of the bookcase, but have actually been reading the entire chapter on viscous flow in ducts (Fluid Mechanics, White, 1986).

    Can’t believe I used to know this stuff, or perhaps the other way around – I can’t believe how much I’ve forgotten 😦

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