pipe up dust collection

[Ray946]

Hi all Would 4 inch or 100mm dwv pipe be ok for complete shop fit out or have you guys have better idea please advice

[BobL]

Hi all Would 4 inch or 100mm dwv pipe be ok for complete shop fit out or have you guys have better idea please advice

Definitely not. You need at least 6" pipe to draw enough air.

But the pipe size is only 1 of 3 critical things which are essential to provide adequate dust extraction
The other two are
1) The dust extractor has to be able to utilise the 6" pipe.
If you have a 1 or 2 HP DC or any DC with 4" connectors it still won't draw enough air.
A 2HP modified according to the sticky in this forum or a 3HP with 6" is minimum. It its a large shed you will need long ducting runs you might need more.
2) The machine ports have to be 6" or multiple 4"
And there has to ben enough air into a machine to allow air and dust to be drawn out of a machine.
This may mean cutting holes in Machinery cabinets.

If you want to avoid bitter disappointment don't even bother with 4" ducting.

[Ray946]

Definitely not. You need at least 6" pipe to draw enough air.

But the pipe size is only 1 of 3 critical things which are essential to provide adequate dust extraction
The other two are
1) The dust extractor has to be able to utilise the 6" pipe.
If you have a 1 or 2 HP DC or any DC with 4" connectors it still won't draw enough air.
A 2HP modified according to the sticky in this forum or a 3HP with 6" is minimum. It its a large shed you will need long ducting runs you might need more.
2) The machine ports have to be 6" or multiple 4"
And there has to ben enough air into a machine to allow air and dust to be drawn out of a machine.
This may mean cutting holes in Machinery cabinets.

If you want to avoid bitter disappointment don't even bother with 4" ducting.

Thanks Bob
6 inch pipe i have not got room for that thickness but i can go to 5 inch with little trimming the stud walls but would love too put in 6 inch also have not told what cyclone i am using Bob it forbe & hare dc3 dust collector and CDS-2/3 - Cyclone Dust Separator i will put the dc3 motor and fan on top of the CDS-2/3 - Cyclone Dust Separator to make same room in outside shed just let you know long point form collector will 8 meter
thanks ray

[BobL]

Others will tell you different but all the measurements I have made using chip catchers or cyclones on smaller dust extractors indicate that these setup leaves too much dust behind in the shed.
The stock DC is not a satisfactory DC either - it has to be modified for it to use 6" ducting to have a chance of getting even close to removing enough dust.

Not sure what you means by " long point form collector will 8 meter"

[Ray946]

What trying to say Bod i have no room for 6 inch pipe inside the work shed but I do have have room for a 5 inch pipe
Would 5 inch pipe be ok for what dust collector and cyclone I have purchase

[BobL]

What trying to say Bod i have no room for 6 inch pipe inside the work shed but I do have have room for a 5 inch pipe
Would 5 inch pipe be ok for what dust collector and cyclone I have purchase

5" may be enough for some smaller machines and processes, so it would be helpful if you listed your machinery and dust making processes

However I cannot say that 5" pipe will be OK for everything and neither will that DC unless it is modified.
Adding the cyclone will make things worse

The "safe" target flow rate for most DIY WW machines is 1000 CFM.
4" pipe can only carry ~425 CFM (before any long ducting and junctions or machine connections are made) and if you put a cyclone in the path way the flow rate will be ~300 CFM. Adding longer length of ducting and junctions and connecting it to a choked machine will drop it even further - some setups with 4" pipe end up with as little as 200 CFM and a very dusty shed.
5" pipe will carry ~765 CFM - once again its downhill from here.
6" pipe will carry ~1250 CFM - now you are over the 1000 CFM so you can afford to use longer ducting more junctions, etc) even so machinery

However if 5" that is all you can fit then that is all you can fit.
Remember ALL your machine ports (including the entire air flow pathway through the DC) MUST be opened up to at least 5" and vents be cut into cabinets so air can flow into the cabinets or machines so it can carry the dust out.

While 5" it's still not ideal I would then suggest employing the following as back up
- wearing a mask at all times you are in the shed
- keeping all doors and windows open
- installing exhausting fans to clear the
- regularly cleaning dust off floors and surfaces since the the fine dust will not be removed while it is being made.
- when you leave the shed get changed so that dust stays on the clothes outside the house.

[QC Inspector]

Not sure why a 6" pipe is too big to fit into the shop but you could if the pipe runs are short make a square duct that is 5.3" to a side and still have the same area as a round duct without much airflow losses. Upside is a shelf to put things on. :)

Pete

[BobL]

Not sure why a 6" pipe is too big to fit into the shop but you could if the pipe runs are short make a square duct that is 5.3" to a side and still have the same area as a round duct without much airflow losses. Upside is a shelf to put things on. :)

It doesn't quite work out that way because of the cross sectional area to perimeter ratio.
A 6" pipe has a perimeter of 18.85" while a 5.3" square has a perimeter of 21.2"
This means the moving air has 12% more wall to interact with in the 5.3: square duct so that will slow it down more than a 6" round duct with the final result being the 5.3" square will act more like 5.6" diameter pipe.
If you want to use square ducting to approximate a 6" duct you will need to use something like 5.8" square i.e. you might as well use 6".

If you use rectangular ducting make sure your smoothly radius any junctions etc.

[QC Inspector]

Thanks Bob, I appreciate your expertise. I was only looking at the cross sectional area of a 6" pipe and that's how I came to the 5.3" square for the inside of the duct. If Ray wanted to use a rectangular duct and keep one dimension to 5" what would the second dimension need to be to equal a 6" round? I understand that the rectangular wouldn't be optimum but it should be better than 4" or 5" piping if the runs are not too long or full of bends.

Pete

[BobL]

Sure I understand.

Actually it turns out the numbers I was referring to were incorrect and were for flow rates significantly more than basic wood working DCs.

At the flow rates for DCs, i.e. ~800 to 1000 CFM, for smooth PVC , a 5.5" square duct will effectively be the same as a 6" round duct, and if one dimension is 5" the other only needs to be 6.1".

It assumes that any square ducting made will be of the same smoothness as smooth PVC.
I think it was Bill Pentz that said if you decide to substitute circular PVC ducting of diameter "X", with square wooden ducting, you should make it "X by X" but I'm not sure what wood he was referring to.

The effect I was referring to really shows up when the smaller dimension of a rectangular opening becomes significantly smaller.
e.g. if one dimension is 1" the other needs to be 60" i.e. about twice the cross sectional area!
if one dimension is 1/2" the other needs to be 190" i.e. about 3x the area

The above is for "flow through a pipe/duct" of those dimensions, flow into a gap is slightly different nevertheless it demonstrates the importance of not relying on narrow slots for ventilation of cabinets. When they get less than 3 mm you can effectively ignore them.

For flow into a gap or port the rounding over of the entrance edge will be very significant

[bill pentz]

Interesting...

I rarely post on the forums as just don't have the time to follow up on the questions. I was requested via email to maybe shed some light on this topic...

Woodworking makes huge amounts of fine invisible dust compared to how little it takes to harm our health. Fine invisible dust is so unhealthy that we have really tough indoor air quality standards. An electron microscope shows wood is made up of very fine very brittle tubes held together with very tough lignin which acts as a glue. Every time our blades, bits, cutters, and even sandpaper touch wood these tubes explode launching millions of tiny invisible particles. These particles are so fine and light they behave more like a bad odor and will quickly spread to all shared air. During woodworking every 20 pounds of sawdust made also makes enough fine invisible dust to cause 15,119 typical two car garage sized shops to fail a typical EPA or EU air quality test, so even 99% efficient collection still leaves 1% which is enough fine dust in our shop air to cause 151 typical shops to fail an air quality test. OSHA testing found most small shop dust collection systems miss collecting at least 15% of the fine dust produced. Fine wood dust lasts nearly forever unless it gets wet enough for biologic breakdown, so this fugitive dust that escapes collection just keeps building. In fact, Cal OSHA testing found that even in very clean looking shops that vent their dust collection systems inside just walking around without doing any woodworking stirred enough fine dust airborne to fail EPA air quality tests.

Decades of experience by those large firms that guarantee air quality from their dust collection systems found air cleaners and venting outside are just too slow to avoid failing air quality tests, so found the only way to pass these tests and amply protect their clients is to build dust collection systems that collect the fine dust as it gets made, then either vent it away outside or into fine enough filters to protect our health. They share exactly how to do this:

1. We have to upgrade most tool hoods. Most blades, bits, cutters and even sanding systems can launch dust filled air streams at over 100 miles an hour (please forgive the Imperial units). Without hoods that block, contain and deliver these dust filled air streams we fail.

2. We all know the lightest breath will move airborne dust, so we have to pull in the airborne dust before normal room air currents blow it all over. Decades of testing found that we need to move right at 1000 CFM at most small shop stationary tools to pull in the fine dust before it gets dispersed by normal room air currents. This translates to providing at least 50 FPM all around the working areas of our tools out to a distance of about 15.25 inches.

3. Venting outside far enough away that the fine dust does not blow back in works best, but if we have to filter then we need at least MERV-15 rated filters sized with at least one square foot of filter area for every two CFM of airflow for typical blended cellulose polyester filters and every four CFM of airflow for the all poly filters. All polyester felt filters are thicker so we don't need as much surface area.

We need a big enough blower. Blower technology is mature so if we go to a blower table for material handling blowers and look up the size and hp needed, we would get near identical results from all the main blower makers. Sadly, testing most small shop dust collection systems show that most have much less efficient blowers. These tables show that we need 3 hp blowers for dust collectors and 5 hp blowers for cyclones to get our real 1000 CFM required when just working with one tool running at a time.

Even with an ample sized blower, we also have to have ducting and tool ports big enough to move enough air. Air at dust collection pressures will barely compress at all, so just like having using a hose, how much water passes depends on the size of the smallest opening. This is why a water valve will let you vary the volume up to the maximum that the size hose you use can carry. That maximum depends on pressure, but at typical dust collection pressures we can only move 349 CFM with a duct speed of 4000 FPM in a 4" diameter sized duct, only 545 CFM with a 5" diameter duct, only 785 CFM for a 6" diameter duct, and only 1069 for a 7" diameter duct. For my designs I use blowers with oversized impellers to generate additional pressures typical of the 4" pipe at 425 CFM, 5" pipe at 765 CFM and 6" pipe at 1250 CFM. Without these oversized impellers that almost no others use, you are going to be stuck at the much lower CFM ratings.

Hope this helps.

[Stewie D]

Excellent information Bill. Thanks for taking the time to explain it all.
Along with other knowledgeable guys on the forum like BobL, I've been a lot more informed of what is required for removing machinery generated dust in the average home workshop. I'm sure others have as well.

Stewie