Flow Rate Dropoff

I’m starting to work on a collection of different air flowrates in the DC system, to see the effects of different fittings, fixtures, and layout on the resulting flowrates.  With this set of data, you can start planning a dust collection run which takes into account the power of the dust collector itself, and just how much you can add to it / distances you can run it and still get an adequate collection rate.

Some initial figures that came out already have me rethinking the location of the dusty itself.  I have it in a separate shed, partly space, partly so any dust escaping doesn’t end up in my breathing air (although with a 1 micron filter on it, that is not really a concern), and the main reason is the noise!  The bigger the unit, the noisier it is.  Air flowing through pipes is noisy enough, let alone hearing the suction unit.  However, the dropoff in performance is remarkable over the distance of run that I have, so I’m wondering now whether I should just bite the bullet, accept the additional noise and have it relocated back to the main shop.  Having it there has the advantage that I can easily turn it on and off as I need it, and clearing blockages does not require a expedition to the other shed.

Hmm, decisions decisions.

The figures that I got on the first couple of DC runs were:

Running the dust collector through the 1st stage collector, and measuring near the tablesaw collection point: 16.1 m/s

Running the dust collector through all the same pipes, but with the 1st stage bypassed: 19.3 m/s

So there is a bit of a loss (expected) of about 15% caused by the 1st stage collector.  That is probably not too bad, so long as you have that extra capacity spare of course.

However, when I measured the flow directly at the DC, I got a reading of 34.3 m/s – double the flowrate that I am currently achieving at the tablesaw.  That is significant, and although I don’t expect to achieve a perfect flowrate, I’m not sure if I should accept such a dropoff.  So my trial is going to be to return the DC to the main shed, and connect it into my fixed collection system with straight PVC piping, rather than having about 2m of the flexible tube at the end that I have at the moment.  Future tests will show just how much of a difference that makes, but I’m just interested in seeing if it makes a significant increase in the TS collection flowrate.

Hmm, much more testing required!

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