More Info on Dust System Selection and Sizing....

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22 Aug 2009
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I posted this material yesterday (i'm currently fairly well up to speed on it, but in a few months will have forgotten lots), but thought it might be useful for some to give it a bit more profile as it sets out to explain why there is so much disparity in the numbers quoted by different dust system suppliers and industry groups.

It's drawn from Bill Pentz's http://www.billpentz.comwork and published data - Clear Vue in the US run by Ed Morgano make fan/cyclone systems to his design.

They seem basically two dead solid and well meaning guys trying to do some good by working to clear the fog of disinformation and misleading claims put up by most of the commercial dust system manufacturers - at what Clear Vue charge for the kit they certainly aren't in it for the money. Bill suffers from pretty poor health at this stage.

I'm relying on their info too in planning my own system. Judging by positive feedback all over the place e.g it seems to stand up 100%. The site is quite spread out, and takes some reading to get to the bottom of, but the data is there.

The genuine reason (even setting the hype and the bull of most commercial makers aside) there's so much disparity in the airflow numbers quoted as being required for chip and dust collection by differing sources is that differing standards are applied.

As he makes clear it depends a lot on what you mean by 'effective' chip and dust collection.

As most of us using basic floor units know you you can collect coarse chips from a saw at 350 cfm/4000fpm using a 4 in duct and 1 hp fan (which smaller duct gives roughly the above provided the duct run is short) and so stay tidy. You won't however be drawing in air fast enough from the volume of space around the blade to pull in the fine sub micron dust it flings about that poses the big health risks.

This situation is made worse by the fact that the bag filters fitted to most 1hp floor units are too coarse to trap fine dust either - much of what you do catch gets spewed back into the shop, especially when the bag is fresh. Plus HP/cfm are a bit marginal even at that so even the coarse chip collection goes south pretty quickly as the filter starts to blind up.

These units typically claim much greater cfm rates, but fairly demonstrably don't deliver what they claim in real operating conditions. (the above has been my own experience with a floor mounted mobile 1hp unit)

When you up the game to saying that 'effective' means satisfying the US OSHA or ACGIH or better still EPA/Euro health and safety at work standards it seems it gets a lot tougher - you need at least 800 - 1000 cfm at your saw/machine depending on exactly what it is.

You basically need 6 in ducting to deliver this efficiently in a smallish shop with fixed ducting.

It's worth noting that while the lower e.g. OSHA US standards were determined by negotiation/trade off with a hostile industry that didn't want the cost, the EPA/Euro standards are based on medical data.

Where this really hits home is when the issue of filtration is added - with a pretty inefficient (open weave - not much use for very fine sub micron dust) bag filter (or exhausting outdoors if the weather is warm) you can probably move this much air with 3hp provided your ducts are fairly short (small garage sized system), and the layout is such that restrictions are minimal.

Up the game to something that's medically correct using something like Donaldson's 262-5001 or 262-5002 UltraWeb 2 Filter Cartridge that's ASHRAE MERV 15 99.99% efficient at 0.3 micron (this is equivalent to the EU standard - sources previously discussed in another thread) and a larger garage sized duct system with one machine connected at a time and you need more like a steady 4hp to achieve this - and will draw more HP if additional ducts are left open. (Bill's blower design uses a 5hp 3,450rpm motor to leave sufficient reserve for this sort of intermittent higher loading)

Fit these finer filters and it becomes highly desirable to install an efficient cyclone that separates the dust and chips before they get as far as blinding or damaging these filters which run about £150 a set. Which is why Bill is into cyclone design as well.

Bill's table in section 1 (c) here sets out the hard test based numbers: ... Basics.cfm

Pardon the length, but maybe it will help somebody. I've seen several uncles/father of friends that worked in the saw/grain milling businesses go down with emphysema in later life, and i've had lots of sinus trouble too - the risk is real.


PS Pentz cyclone made by Clear Vue in action:
thanks for that - have been looking at the cyclone stuff as the "ultimate" solution for some time however a couple of recent threads here have moved me to try the convoluted drop box type idea before using a cyclone as they look easier to make. I will still be using a significantly powerful motor (3-5hp) and a Donaldson filter (talking to them in the new year) along with some form of muffler or silencer if needed.

Thanks for the product codes on the Donaldson things though.

Once I get this off the ground I will post some form of WIP.