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  1. #1
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    Apr 2020
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    Default What size dust extractor.

    Hi all I'm new to the forum, have been watching from the sidelines for a while.
    It seems the more I look into dust extraction the more confused I get. I'm about to re-organise a school woodwork shop, currently finalising scale drawings of the placement of machines in regards to work place health and safety requirements needed for each machine and that a 1m walkway through the shop to exits to meet the needs of fire evacuation are met, which will be painted on the floor.

    The machines in the shop are as follows.

    Table saw
    Thicknesser
    Planer
    Large Band Saw
    Small Bandsaw
    Mitre Saw
    Routertable
    2 x Mortiser
    2 x Drill Press
    2 x Disc Sander
    Disc and Belt Sander
    Boppin Sander
    A future custom made downdraft table
    A future drum sander

    Was thinking of a floor sweep dropper in a few areas but we are talking school students here, and they will just sweep anything into those, mainly small offcuts of timber and don't want to risk damaging the impeller.
    Obviously all machines will have blast gates, the dust extraction motor and filter will be housed outside of the woodwork shop and will have a building built to suit the dimensions of that unit.
    I'm very adamant about fine dust particles floating in the air and to stop that we need a dust extractor that can capture it at the source. In the shop next door where the wood work benches are and the hands on manual tools, sanding etc, I have installed 2 x gravity louvered wall extraction fans that pulls out any floating dust particles, and does so very effectively, as well as pull fresh air in from outside, (the rooms were quite hot before).

    I have looked over the forum and cant seem to find a situation that is similar, they are usually a much smaller shop and therefore a smaller HP extractor is only needed. I'm not sure if 5Hp is enough or up to 10Hp or something in between.

    Thank you for taking the time to read my post and if you can offer any suggestions that would be very appreciative.

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  3. #2
    Join Date
    Feb 2006
    Location
    Perth
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    Schools are supposed to meet workplace OHS requirements so I would initially suggest a bigger rather than smaller DC. My observation about dust extractors used by schools is that every time a school upgrades their wood workshops they usually upgrade their DC to something bigger. A recent pro level upgrade I saw for a two classroom set of workshops used a 15HP DC and a 20 ft high cyclone. The ducting was all spiral galvanised with most going down to 4" on machine so sometimes I wonder if these so called professional people know what they are doing. The sort of approach seems to be lets fit everything with 4" ducting - oops its not working - so then lets fit the biggest DC we can get them to pay for. Maybe if they had run 6" ducting to machines they could have got away with something smaller. Schools like government work places often get taken advantage of in this way.

    WW classrooms are more like a large mens shed than a full production workshop. How many square meters is the workshop(s) and how many students might be at work ta the same time.

    Interestingly, in a survey of all wood related employment sectors. wood work teachers (and students) had one of the lowest overall exposures to wood dust.

    I'm very adamant about fine dust particles floating in the air and to stop that we need a dust extractor that can capture it at the source. In the shop next door where the wood work benches are and the hands on manual tools, sanding etc, I have installed 2 x gravity louvered wall extraction fans that pulls out any floating dust particles, and does so very effectively, as well as pull fresh air in from outside, (the rooms were quite hot before).
    Ventilation is a really good idea but given those louvre fans are not very efficient do they come close to 20 air volume turnovers per hour? Unfortunately it's not possible to tell using eyesight if the most dangerous (less than 2.5 microns) dust is being removed as it cannot be seen with the naked eye. Maybe you could get your school to invest in a basic dust detector?

    Something like this is better than nothing. Just bear in mind you may kill it if you move it too close to a dust ladened air stream eg coming from a power tool or machine.
    https://www.ebay.com.au/i/3524954804...xoCjNAQAvD_BwE

    These are best kept on a shelf at least a metre or two away from a dust ladened air stream.

  4. #3
    Join Date
    Nov 2007
    Location
    melbourne australia
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    Quote Originally Posted by Robgib View Post
    Was thinking of a floor sweep dropper in a few areas but we are talking school students here, and they will just sweep anything into those, mainly small offcuts of timber and don't want to risk damaging the impeller.
    I agree with you about the students, but I assume the system you need will include a cyclone. That should remove any chunks before they reach the impeller.

  5. #4
    Join Date
    Apr 2019
    Location
    NSW
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    37
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    Default

    some mesh in the floor sweeper pipe would help stop stupid things going up into it.

    but yeah i'd tread fairly carefully about what system gets put in place, i'd be looking into the australian standards you'd hate for a parent to get involved when billys asthma starts acting up only to find out your system doesn't comply.

  6. #5
    Join Date
    Apr 2020
    Location
    Sunshine Coast
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    Post

    BobL

    Thank you for feedback. I agree wholeheartedly the waste of money governments and schools seem to waste, I'm a bit of an over the topish research into anything I personally buy and I guess this is an extension of who I am, it's not my dollars but I am treating it like it is. I want the right product the first time and also a good bang for the buck so to speak. If I get a couple of quotes from some DC companies and they start talking jargon and maybe spinning some , hopefully with the time and effort I have put in I can see that some companies might be pushing for larger DC more than what is required, they are a business after all and upselling overtop more than what I need.

    The volume of the classroom that has the 2 extraction fans is 254 m/3. Each fan produced 16 000 m/3 per hr. I installed the largest fans possible. If my calculations are correct that is 125 times per hour the air volume exchanges.

    Thank you for the heads up on the air detector, will definitely be purchasing that.

    Is there something that can measure CFM for a DC to make sure it is performing as well as it should be?


    haveabeer69

    Mesh in the floor sweeper pipe, I like that thank you.


    jack620

    Yes definitely a cyclone and your right anything as heavy as chuncks of timber should drop down through the cyclone before going through to the impeller.

  7. #6
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    Perth
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    Quote Originally Posted by Robgib View Post
    The volume of the classroom that has the 2 extraction fans is 254 m/3. Each fan produced 16 000 m/3 per hr. I installed the largest fans possible. If my calculations are correct that is 125 times per hour the air volume exchanges.
    Hummm . . . . . are you sure about 16,000 m^3/hour - thats equivalent to ~ 10,000 CFM this would require some 10's of HP to move that much air.
    Can you perhaps send me a link to the fan specs?

  8. #7
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    Location
    Sunshine Coast
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    Post

    BobL
    Here is the link to the exhaust fan, I hoped I have not be taken for a ride with there numbers, but all the teachers are very impressed with the amount of breeze coming through the class, anyway see what you think.


    New 2020 Gutto industrial supplys 24 inch extraction fan 240 volt auto shutters FREE SHIPPING ON MACHINES 4U Axial Fans in SOMERVILLE, VIC

  9. #8
    Join Date
    Aug 2008
    Location
    Melbourne
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    Quote Originally Posted by Robgib View Post
    Yes definitely a cyclone and your right anything as heavy as chuncks of timber should drop down through the cyclone before going through to the impeller.
    I'd be going for a "clean air" system where the fan is after the filters so there never any risk to it. Reverse pulse filter cleaning will also help keep it running as effectively as possible. Something like the Leda GOVE systems GOVE: Specialised Extraction for Woodworking Companies - Leda Machinery

    My old work was on a 15hp system which struggled to keep up with our requirements (after we got a giant wide-belt sander and CNC router it was definitely not enough). I think it would handle your setup, as long as you properly managed which machines were getting suction with blast gates, but not less that 15hp.

    Quote Originally Posted by BobL View Post
    Hummm . . . . . are you sure about 16,000 m^3/hour - thats equivalent to ~ 10,000 CFM this would require some 10's of HP to move that much air.
    Can you perhaps send me a link to the fan specs?
    Leda quotes 16,400 m^3/hr @3500pa on 22kw, so that's 30HP

  10. #9
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    Perth
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    Quote Originally Posted by elanjacobs View Post
    My old work was on a 15hp system which struggled to keep up with our requirements (after we got a giant wide-belt sander and CNC router it was definitely not enough). I think it would handle your setup, as long as you properly managed which machines were getting suction with blast gates, but not less that 15hp.

    Leda quotes 16,400 m^3/hr @3500pa on 22kw, so that's 30HP
    I forgot the 10s of HP would be for a pressurised system (ie cyclone / filters). It is possible to move lots of air at low pressure ie ventilation with VERY LITTLE HPf HP. My two squirrel cage fans are 1/2 and 1/4 HP and can move 4700 m^3/hr and there are AC fans thaT CAN move more than 10,000 m^3/hr with 3HP motors.

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