Thread: Flow loss using a Dust Deputy

Good job Bob, and thanks for your efforts - everyone can benefit from information.

As a suggestion for tracking down what happens with the very fine dust: if you weighed the filter, bag, rest of the vac and then compared the weights afterwards that would tell you exactly how much dust was not left in the system. Also, IIRC, you have the instruments to measure fine dust, so perhaps you might be able to get a handle what % is in the mix?

Perhaps the latter poses too many difficulties, or buggerising around, but certainly the weights would be really interesting.

It would also be interesting to see what happens with a Festool vac, given that they like to be seen as (the?) top notch. Yes, I own one as you know, but I'm not a prejudiced fanboy who sees no wrong and only stars and hero worship. Things are what they are. Having said that, I do think the are great shop vacs.

Originally Posted by FenceFurniture

... but I'm not a prejudiced fanboy who sees no wrong and only stars and hero worship.

Ahem, Liogier.

Originally Posted by Bohdan

BobL

I have a question in regards to the test dust used in your test. Was it sourced from a DC which is a HEPA system and did it include the very fine dust from the HEPA filter?

No HEPA. My DC has twin, thick needle felt bags and is located outside my shed.
The filtration efficiency with conditioned bags is >99.35% down to 0.7 microns, 98.18% between 0.7 and 0.5 microns and 93.55% between 0,3 and 0.5 microns.
This means there is plenty of very fine dust in the bags - certainly more than enough to perform this experiment. What I would like to do is find some very fine dust and try this out. I could sacrifice a 1/2kg bag of flour but I would rather use actual wood dust.

I would like to add that I am really interested in the outcome of your experiments as I am using a DD with a Festool HEPA VC for sanding, routing and sawing with the track saw and find that it works really well and have not had to empty the VC bag for several years despite emptying the DD sometimes weekly.

I am surprised you are not seeing something with the HEPA filter, even if there is a leak in the VC they are usually not 100% efficient at losing all the dust.

Originally Posted by woodPixel

Ahem, Liogier.

There's a difference between being a fan (which I am of Liogier) and a Festool Fanboy who can see no fault with anything they do (refer to my post here on DE for the CMS). Fanboys accept no criticism of the brand, no matter how justified.

Anyway, let's stay on track.

Originally Posted by FenceFurniture

Good job Bob, and thanks for your efforts - everyone can benefit from information.

Cheers FF - I don't have an immediate need for a DD and cannot see a situation where I might need one in the future, but a number of woodies have asked me about these and without direct experimental evidence I have found it tricky to provide advice.

As a suggestion for tracking down what happens with the very fine dust: if you weighed the filter, bag, rest of the vac and then compared the weights afterwards that would tell you exactly how much dust was not left in the system..

This is a good suggestion. Handling the paper cartridge filter from the Ryobi W&D would be quite tricky because the dust would fall off the paper pleats quite easily when handling it. Even just opening the VC knocks some dust off the cartridge. Perhaps carefully opening the VC and then immediately placing the motor and cartridge in a plastic bag and then removing the cartridge would be possible. Then I could weigh the filter inside the plastic bag.

[QUOTE] Also, IIRC, you have the instruments to measure fine dust, so perhaps you might be able to get a handle what % is in the mix?

Perhaps the latter poses too many difficulties, or buggerising around, but certainly the weights would be really interesting.

It would indeed be interesting but that is one thing I can't really do easily without as you put it - buggerising around. I cannot poke the particle counter into a bucket of dust or into a duct carrying the dust as this will damage the machine. This happened to BP when he let a friend borrow his particle counter and the friend placed the probe into a duct carrying dust and the counter was damaged beyond repair. What I have to do is dilute the dust down to below the level so the sensors in the counter are not overwhelmed by the amount of dust. There is a way to do this by putting milligram amounts of the dust into a large chamber and fluffing it up with a powerful fan but that's too much mucking around even for me ;-)

It would also be interesting to see what happens with a Festool vac, given that they like to be seen as (the?) top notch. Yes, I own one as you know, but I'm not a prejudiced fanboy who sees no wrong and only stars and hero worship. Things are what they are. Having said that, I do think the are great shop vacs.

They are definitely in the best range but like all VCs they too have difficulties long term. I have never found any vacs more than a couple years old that do not leak. Some leaks can be repaired but you have to know where they are to do this.

Originally Posted by Kuffy

This comment sparked my interest. I hadn't actually checked the inside of my shopvac since connecting it to a cyclone because it was still sucking well enough and I know that when the bags are full, the sucking reduces badly, no different to any standard vacuum cleaner that is used to clean carpets. To be honest, I was expecting the vac bags to be partially filled, as well a fine layer of dust covered all over the inside of the shopvac.

as expected, the first thing I noticed was a layer of dust on my pre-filter protection condom bag (i don't know what it is called...). a layer of dust around the inside of the shopvac housing. a fair amount of fine dust (mostly fines, no big chunks) inside the vac bag.

You are one of the few DD users who admit their DD lets though a significant amount of fine dust. The usual claim is "about a teaspoon every few months" - through to "clear as a bell after one year of use".

What appears to be happening is the shop vac filter, the condom bag and the shop vac bag are acting as a multistage filtering system. This can be a useful approach at reducing the amount of fines escaping from a VC especially for folks who cannot vent their VC outside i.e. using a VC inside a large building although a HEP filtered VC would be the way to go in that situation.

Where did you get the condom bag from as I wouldn't mind testing its filtration efficiency if they are not too exxy.

The paint bucket is collapsed in around the sides due to the vacuum pressure inside the bucket. I need to find a stronger or better shaped bucket so it doesn't collapse. I have probably emptied that paint bucket of dust/shavings about 6 times since connecting the cyclone to my shopvac. The shopvac paperbag is about (rough guesstimate) 25%-35% full of nothing but fine dust.

That's very interesting and suggests you should be emptying the shop vac bag on a more regular basis because even though you don't realised it, any fine dust in the bag will reduce the overall Vc flow rate. The "feel" or "sound of the "suck" means very little compared to an actual measurement, by the time feel and suck are noticeable the actual flow can drop as much as 50% especially as this tend to happen very slowly over time. For maximum flow you should empty the bag every time you empty the DD bucket or at least every second or 3rd time. To some extent this defeats the purpose of a DD.

Originally Posted by BobL

BTW 46 g of dust distributed throughout a shed that is 6x4x2.7 (64.8 m^3) = 679 mg/m^3 or 710 times above OHS levels for hardwood (1 mg/m^3).
Even if the efficiency of the DD was 1% that's still 20g of fine dust that goes straight through the VC and produces ~300x above OHS levels for the same sized shed.

I just want to clarify this in terms of real practice.

Actually making 2000g of sawdust, and injecting 46g of the very fine dust component into a 6x4x2.7m shed to generate 679 mg/m^3 or 710 times above OHS levels for hardwood (1 mg/m^3), is not that easy to do, and depends very much on the actual DIY WW practice.

The reason for this is that the dust has to be generated and dumped in one shot which simply does not happen.
If the sawdust is produced gradually the fine dust will fall out of suspension with a half residence time in air of about 30 minutes.
Add to this any sort of even moderate ventilation and the levels will drop further.
However these factors are not usually enough to reduce levels to less than recommended values

To actually make 2kg of sanding dust with an ROS will take many hours so the levels won't very reach any where near those stated above but it will still easily exceed recommended levels unless some extraction is undertaken.

Here are a few examples of rapid dust production.
Thicknessing: 2.4m x 100 mm x 1 mm passes generate about 120g of wood dust so 17 such passes will generate ~2kg of wood dust.
Ripping: ~6, 2.4m x 100 mm x 3mm kerf passes will generate ~2kg of wood dust
Vacuuming a floor doesn't generate the dust from wood but it's still passing a lot of fine dust through a VC and that can easily raise the dust levels in a shed well above recommended values
Roughing down a large turning blank, drum- large belt sanding also make a lot of dust.
Machine sanding is problematic because it makes more fine dust that other machines.
Keep blades as sharp as possible also reduces fine dust production.

Bob, I bought the cloth pre-filter from bunnings. Mine was ryobi branded but I couldnt find that one in their catalog. Found this one, but it looks small.....
https://www.bunnings.com.au/powerfit...ilter_p6210462

Thanks for doing the tests BobL. Interesting to see the results.

I (and presumably many others) would be interested to test the efficiency of larger cyclones that are intended to be used with large DCs. For example, I'd be interested to know what sort of air flow reduction you get by hooking up a CDS 2/3 to a DC-7 (as mentioned by Nifty Nev). I'd also be interested to see how much impact a well made Thein top hat (with 150mm ports) has.

I've stayed away from using any sort of separator as I don't have the money for a CV cyclone (even just buying the cyclone on it's own) and I'm working on the assumption that cheaper cyclones, or home built options, reduce flow by an unacceptable amount. But I'd be keen to put that assumption to the test. Or more specifically, get someone else to put that assumption to the test as I'm too lazy to do it myself.

Originally Posted by WoodyNZ

I've stayed away from using any sort of separator as I don't have the money for a CV cyclone (even just buying the cyclone on it's own) and I'm working on the assumption that cheaper cyclones, or home built options, reduce flow by an unacceptable amount. But I'd be keen to put that assumption to the test. Or more specifically, get someone else to put that assumption to the test as I'm too lazy to do it myself.

Any cyclone reduces air flow and I think the CV is the worst as it is also the most efficient in separating the dust from the air. Phil Thien has always been evangelistic about the efficiency of his invention and absolutely refuses to see any criticism of it at the same time criticising the need or use of alternatives such as large ducted systems. He may well be right but if it has a VC connected to it the VC is usually an issue on its own. I have often though a ducted vacuum system as used in a house would be ideal for a workshop where high velocity is needed and the units are not that expensive.

Originally Posted by Kuffy

Bob, I bought the cloth pre-filter from bunnings. Mine was ryobi branded but I couldnt find that one in their catalog. Found this one, but it looks small.....
https://www.bunnings.com.au/powerfit...ilter_p6210462

Thanks, that's cheap enough for me to buy one and test.

Originally Posted by WoodyNZ

Thanks for doing the tests BobL. Interesting to see the results.

I (and presumably many others) would be interested to test the efficiency of larger cyclones that are intended to be used with large DCs. For example, I'd be interested to know what sort of air flow reduction you get by hooking up a CDS 2/3 to a DC-7 (as mentioned by Nifty Nev). I'd also be interested to see how much impact a well made Thein top hat (with 150mm ports) has.

Having been around to nearly 2 dozen sheds I have seen some "interesting! home made separators all of which significantly reduced their overall flow

Some home made style separator flow reduction measurements are reported by me in this thread.
Chip Collector performance

I would like to have the time and access to test more of this type of gear but I only do it as the opportunity arises because it takes a lot of time.

I've stayed away from using any sort of separator as I don't have the money for a CV cyclone (even just buying the cyclone on it's own) and I'm working on the assumption that cheaper cyclones, or home built options, reduce flow by an unacceptable amount. But I'd be keen to put that assumption to the test. Or more specifically, get someone else to put that assumption to the test as I'm too lazy to do it myself.

BP has done some testing in terms of pressure loss. I prefer to report actual flow rate losses in specific circumstances as more DIYers are likely to understand this than pressure losses.

The Clearvue design has one of the lowest pressure drops for any cyclone, and hence flow losses of all cyclones. According to BP, the Clearvue generates a pressure loss of 2.25" WC, compared to double that for home made separators and cyclones. What is often missing on other cyclones is the ramped air inlet which on correctly sized cyclones can drop the pressure losses from 4.5 to 3" WC.

The greatest flow for any system is still achieved using no cyclones and large clean filters. eg pair of large clean pleated filters can have a pressure loss as low as 0.1" WC. The issue then become's one of ease of emptying the dust and cleaning the filters. For someone like me who only need to do this a couple of times a year I still see no need to go to a cyclone. While I'm doing the emptying and cleaning I bitch and moan but then when its all over its quiclly forgotten.

Originally Posted by BobL

For someone like me who only need to do this a couple of times a year I still see no need to go to a cyclone. While I'm doing the emptying and cleaning I bitch and moan but then when its all over its quiclly forgotten.

I had a day a few years back now when I had to empty the bin (44 gallon drum) on my home-made cyclone four times. That was (hopefully) a once in a lifetime event, a really full-on day. This was ripping timber for battens to enclose under my house in Queensland and running them through a thicknesser. I worked it out that this involved pushing more than a kilometer of timber over a triton workcentre, four cuts per batten, and probably 400 metres of thicknessing. Just thinking about it now makes my back hurt.

Today for regular shed activities I need to empty my cyclone a lot more than a couple of times a year.

BobL, as you say, a couple of times a year emptying the DC you can quickly forget the inconvenience, whereas for me, I love the convenience, speed and low exposure levels in being able to just empty the cyclone collector and get back to work.This probably explains the differences of opinion we have had over the years about the need for cyclones. Yes, the CFM may be reduced but I have employed other methods to control fine dust that the system does not get, such as exhaust fans etc. There is no "one size fits all" solution

Cheers

Doug

Originally Posted by doug3030

BobL, as you say, a couple of times a year emptying the DC you can quickly forget the inconvenience, whereas for me, I love the convenience, speed and low exposure levels in being able to just empty the cyclone collector and get back to work.This probably explains the differences of opinion we have had over the years about the need for cyclones. Yes, the CFM may be reduced but I have employed other methods to control fine dust that the system does not get, such as exhaust fans etc. There is no "one size fits all" solution

If you are pushing a kilometre of timber through a work centre then using any sort of chip catcher or cyclone on a small DC will most definitely not have the flow to be able to capture the fine dust in the first place. Then, of the dust that is captured it will simply not separate out the very fine dust component and that will pass straight through the DC and its filter.
All in all a lose-lose situation.

A 50 mm wide cut through 1km of timber with a 3mm kerf = 150,000 cm^3 of timber at 0.5g/cm that is 75,000 g or 75kg of sawdust.
Any sort of home made chip collector will be at best 95% efficient at dust capture with the 5% not captured being invisible dust that will sail right though your chip collector and DC filter.
5% of 75 kg = 3.75 kg of fine dust which in a 65m^3 shed makes >57000 time above OHS levels.
Even if your chip collector is 99% or 99.9% efficient it will still be over the limit.
This is another reason why DC should be located or vented outside.

However this wont help the dust that is not captured to begin with.

BTW The exposure during the relatively short time it takes to empty a DC bag and filter pales into insignificance compared to the sorts of long term exposure that involves ripping a km of timber.

And whatever you use, unless you are monitoring the dust levels in your shed with a particle counter you are only guessing what the dust levels really are.