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23rd July 2020, 09:45 AM #1Senior Member
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Dust extractor filter - required after cyclone?
For several years I've been using a H&F 2hp dust extractor, with a needlefelt bag on top. It's in my woodworking shed, but by the door (full side of shed sliding door) which is open when I'm working. This has served me well, but I've just purchased (yet to be delivered) a Carbatec add-in Cylcone as an uppgrade. The extractor connects to all my machines, except RO sanders which have their own system.
To improve the system I've been thinking about moving the extractor (or at least the filter) outside, building a lean-to extension on the shed to accommodate it. However it occurs to me that the entire filter system may be unnecessary. I live on a farm, my woodworking shed is several hundred metres away from my house, and surrounded by farm sheds, cattle yards and dusty dirt roads and laneways. The advertising blurb for the Carbatec Cylcone says it removes 99% of chips and dust........... which leads me to wonder whether the needlefelt filter is actually required at all..... If I simply exhaust the extractor out through the wall of the shed (away from the door), will the 1% dust remaining will simply drift away? Will it significantly add to the huge amounts of dust in the air from everyday farm activity?
Can anyone who has one of these cyclone units comment on how much dust actually gets through to the filter? Or have any other thoughts on the requirement for final filtration when located away from civilisation?
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23rd July 2020, 10:04 AM #2.
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The ideal location for exhausting the DC would be outside the wall OPPOSITE your big shed sliding door.
Locating a DC by a door and using ducting going back into the shed creates a low pressure back inside the shed and a high pressure by the door so the fine (invisible) dust emitted by the DC will (weather dependent) just drift back into the shed - you won't see it but it will be there.
You can indeed install a cyclone on a DC and if you vent the DC outside you won't need filters but be aware that adding a cyclone to such a small DC will reduce the flow leaving more fine dust back at the source. Cyclones should really only be used on large DCs which have the initial grunt to cope with the flow losses
The flow on the stock generic 2HP DCs is pretty ordinary but can be improved significantly by modifying them according to the sticky at the top of this forum but putting a cyclone on them will just take them back to square one.
Most DIY fine dust can be handled by adding ventilation via exhaust fans.
Something between a few bathroom exhaust fans and this one should do it
IBigAssFan2.jpg
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23rd July 2020, 10:50 AM #3Senior Member
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Thanks Bob!
I figured that if I were to exhaust the system outside, I would indeed do so at the back of the shed. Currently the extractor being by the door does have the potential for fines drifting back inside, but in a farm situation, with a door that is perhaps 4m high and 6m across there is enough dust drifting in that a little extra may not matter!
Interesting that a 2hp extractor is questionable for a cyclone. Both H&F and Carbatec sell combined (integrated) cyclone/2hp systems,as well as selling and recommending "my" cyclone specifically for the 2hp standalone extractor. I'll see how it goes and make a judgement!
Sadly I don't think I have a photo, but my farm was previously owned by a gentleman with connections to the mining industry. When I bought the property he simply walked away leaving everything in place. One item was a "fan"... It was a fan in a long duct, the revolving "blades" part must have been 5 to 6 feet across, with the duct significantly bigger, reminiscent of a jet engine (but much heavier as befits mining equipment!). I sold it to a company that did special effects for movies......!
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23rd July 2020, 10:58 AM #4Senior Member
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Found a picture!!
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23rd July 2020, 11:29 AM #5Intermediate Member
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Now that's a FAN...........
I am not an expert like BobL but this is my understanding of the matter:
Large professional workshops usually blows out the dust and use either a cyklone or a simple cotton bag filter to separate the coarser dust from the air. The fine dust just settles and disolves. In a hot climate like you have in Australia this seems to work all right as long as the air outlet is far enough from the door or any opening where the dust can be sucked back in by the low pressure created inside the building.
However in the much colder climate that I live in this requires a hugely oversized heating system to keep up with the heat loss. When you have let's say -25 celsius outside (which is not too uncommon to have for a couple of weeks at a time) and the entire volume of air in the building is cirkulated several times per hour the heating costs quickly add up even if you can cope with an indoor temperature of only +10 celsius or so. If you have a great turnaround of profitable products going out the loading dock by the lorry load every day that is all right but for a small business operating on the present day market with small profit marigins the heating cost may at times end up being the last nail in the financial coffin. Firewood is free but taking a month off every winter to make enough of it reduces incomes.
Hence many small businesses recirkulate the air. Most of them use very basic filtration and very many get the consequent respiratory problems like KOL or allergies or asthma. In later years some have started using proper filtration either with a coarse filter followed by a fine filter or by a cyklone followed by a fine filter.
With that background knowledge applied to your situation I can see two ways of doing it. Either lead the fine dust outside far away from the door or filter it very thoroughly through fine filters. Your fan does not have enough power to blow the dust through a cyklone followed by a fine fiter.
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23rd July 2020, 12:21 PM #6.
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23rd July 2020, 08:49 PM #7Senior Member
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It's not at all unusual for shops in the suburban US to exhaust a cyclone directly outside. Many rural shops skip the cyclone and vent the fan with just a duct.
Bob is right about adding a cyclone to an existing system. It adds resistance and thus reduces flow rate. You can more than compensate for the cyclone resistance by removing the things that are no longer needed. These include the bag of course but also the separator ring and it's connecting hose along with the transition on the fan exit. Get rid of all of those, put the fan on top of the cyclone and vent straight outside and you will end up with a good improvement in airflow performance instead of a loss.
I don't have any data on the Carbatec cyclone but I do know that the Oneida SDD has less resistance than the separator ring alone on my "2HP" DC.Dave
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24th July 2020, 12:38 AM #8Senior Member
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Have had people getting up me in the past for suggesting such things - but you seem to have the place to do it. In the burbs -well not so. Old school woodworking factories simply had a cyclone on the roof with a rain cap on the top - would let the wind do what it will with the very fine dust. Obviously removing all filters will help inside the shed ( and move it outdoors) Sawmills also used to burn all their waste. No more. Be aware of houses etc. close by and wind etc. Having free flow on the shed end will be notable however.
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24th July 2020, 02:37 PM #9Senior Member
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Thanks everyone, all very helpful!
I'll have a look at the extractor (when the cyclone arrives) and see if I can mount it directly on top. As long as the fan and motor bearings (whatever they might be, I haven't looked yet) are OK with the motor shaft vertical, that will lety me directly connect the units and use a straight pipe to go out through the back wall of the shed.
The heating and cooling issues I completely understand from previous workshops, but in this case it's an unlined Colorbond farm shed with no heating or cooling - I've considered installing a woodburner or diesel fired heater but on anything other than cloudy days I just have the door fully open and stand in the sun!! To cool it in summer would require complete lining and insulation (and somehow sealing the large sliding doors) which on a 100sqm farm shed would be a costly undertaking!! I just put up with it, or avoid working in the afternoons!
Thanks again!
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24th July 2020, 06:33 PM #10GOLD MEMBER
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Thanks for bringing that up. You beat me to it. Unfortunately the standard mantra around here is that if you add a cyclone you will reduce performance. That's true IF you don't change anything else. If you remove the bag and vent outside OR replace your needle felt bag with a couple of pleated filters you will get an increase in performance.
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24th July 2020, 07:44 PM #11Senior Member
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25th July 2020, 06:23 AM #12
I've been looking for detail on the performance reduction of the bag/filter/ring part of the whole setup, so am interested to see it noted in your post.
Will you please share how you calculated it, or your source so that I can follow this particular tunnel of the rabbit warren a little further.
I had planted on running my own tests with a manometer in the next several weeks, but your info may be able to help my thinking in the interim.
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25th July 2020, 07:06 AM #13Senior Member
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I was doing some testing on an impeller substitution and, since I was already setup for measuring fan curves, started taking things off the DC until I got it down to the bare blower. I ran a fan curve at each step.
Many Configs.jpg
Panorama3A.jpg
Note that the filter bag is in new, unused condition so shows almost no resistance. The pleated filter has been well used and cleaned.Dave
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25th July 2020, 09:43 AM #14
I run a home-made cyclone made from two 44 gallon drums powered by a modified 2 hp blower as per the "sticky" at the top of the dust forum. I have done so since before BobL documented his build and made it popular. No filters or collection bags and 6" ducting.
I'm not worried about my warm or cool air (depending on the season) being sucked out of my shed because my shed is in two parts - the room I do most of the work, which is air conditioned and the main machine room which is not air conditioned. I go out to the machine room to make the main dust and then retreat to the air conditioning to do the majority of the work. In a more extreme climate that may not be practical.
The modified 2 hp blower sits up on top of the two 44 gallon drums and vents directly outside through the wall of the shed. I am in the suburbs. I have never had a problem with whatever dust gets through the cyclone. It just goes away with the wind. You would have no problems in a rural setting doing that - if your cyclone is efficient. The cyclone may well take some suction out of the system but the removal of the filters makes up for at leas some of that. The real advantage I see in doing it this way is that I don't have to handle dust bags and needlefelt filters. I just wheel out the bottom 44 gallon drum on a trolley and empty it.
My system is dismantled at the moment as I am overhauling it and repainting it as I install the automated blast gates etc which I have had sitting in their boxes for a year and a half now waiting for a chance to install them.I got sick of sitting around doing nothing - so I took up meditation.
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27th July 2020, 01:39 PM #15Woodworking mechanic
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