Dust Collection Miscellaneous
OK fasten your seatbelts, here I go again, long winded and opinionated as usual.
Let’s start off with this. I spent a whale of a lot of hours over a period of months reading everything I could find about dust collection. I did the calculations for air flow, static pressure, duct size, duct type, etc. I read what Bill Penz had to say, I purchased books, I had the library get books from other libraries, I was just plain old DC saturated.
My own personal system seems to be working quite well. I do a lot of duct rearranging every time I purchase a new major tool.
In general keep in mind that anything that gets in the way of the airflow in a DC is going to cost you. Air has to come in EASILY to replace air that goes out. Straight lines of air flow are most efficient. Use the shortest runs practical. Pipe size needs to be large enough to move the air freely. Pipe needs to be smooth, not rippled like flex pipe.
My response to Chuck’s original questions:
1 Definitely use two 45* (* means degree) ells to make a 90* turn. This disrupts the air flow much less than a 90*. Use a Wye instead of a Tee for the same reason. Two HP units should not have to cope with 90* turns.
2. I have not used thin wall ducting. From ignorance I did overkill and used SandD schedule 35. I could not find anything that told me how strong the duct walls needed to be. I did find references that stated the thinner venting ducts would collapse in a DC situation. However, that was it.
Some thin wall PVC has rippled interior walls, like flex ducting. DO NOT use it. It has triple the drag of smooth wall.
3. I have used only friction fitting of joints in my DC. It is quite satisfactory. I have no leakage. My son Glenn has done the same. Neither of us has taped any connections.
4. I am not familiar with the HF dust collector. I will try to see one tomorrow. In my opinion, HF stuff can be a tremendous bargain or junk.
Sorry Rich but the air does not need to be returned to the DC room. However, some way the air that is removed has to be replaced with more air or the expelled air. I built an addition onto my shop to house the DC. I did it specifically so that the filtered air was NOT returned to my shop. I did not want the invisible pollutants returned to my shop.
There was a several page technical report about static electricity causing a problem with wood dust. It was on Saw Mill Creek about the time FWW was started or it might be on FWW back then. This was a report by a chemical engineer on what it takes to make a fire/explosion with wood dust. According to all of his technical jargon and research references, it cannot be done with static electricity. The result was that I used PVC and I did not run wire along the outside of the PVC.
Metal ducting was VERY much more expensive than PVC. One joint I purchased for my system was less than $15.00. In metal it was $90.00 plus.
We think and talk about vacuum with vacuum cleaners, shop vacs, and DCs. We are not dealing with vacuum. We are dealing with air movement. The air movement, if correct, will carry the wood dust and the pollutants with it.
There is a kind of dance going on, very similar to sewage movement. If the water moves too fast, it will run off and leave the solids behind. If the water moves too slowly, it will not carry the solids with it. We have to move the air fast enough that the solids will not settle. We have to move it slowly enough that wood chips do not become bullets and ruin the system.
Recently I moved part of my DC ducting. The duct had been in place over four years. The inside of the pipe was sparkling clean except at joints. There was a little ring of dust that smoothed off the area where the pipe met the elbow (or whatever). That ring of dust was packed quite solidly. It was less than half a teaspoon per joint.
Remembering that the job of the DC system is to move air, we do not want to do anything that slows that air as it goes down the tube. We do not want it turbulent the way the rings in flex, make it turbulent. We want the plumbing to be large enough that air friction along the tubing walls is not a problem. We want the gentle turns (and as few as practical) so the air molecules are not crashing into each other slowing down the flow.
Jonathan is correct. You do not want the DC unit “…anywhere near the furnace/boiler.”
Looking at the pipe there are a couple places you will note the slight dust ring. The ring forms where the end of the pipe is tapered for easier insertion into the fitting. It can be as wide as 1/8 inch and at worst 1/16 inch thick.
These pics are old. There is more pipe now. There is less flex now.
At the bottom end of the drop to the lathe there is a 2 1/2 inch wye. From it two of the adjust and let go type ducts run under the lathe bed. I can pull them up with the end(s) into the dust and chip stream from the lathe. This is quite effective.
Enjoy,
Jim