Separating Air and Chips in a Dust Collection System
A shop owner gets advice on how to keep his dust collection system's exhaust side from blowing the tarp off his wood waste pile.September 29, 2014
Question (WOODWEB Member) :
Currently I have an 8" pipe running from my Logosol dust collector through the wall to a dump trailer with a tarp over it. The problem is that the air pressurizes the trailer, lifts the tarp, and chips shoot through every little opening, resulting in piles around the trailer when I run a lot of wood. I also use the trailer for other things and tarping/untarping is a pain. What I’m looking for is a way to separate the outgoing air from the chips so at the end of the pipe they just gravity drop either onto the open trailer or onto the ground to be scooped up later. I'd like to do this as simple as possible/least expensive as possible, but I’m coming up blank on an idea that would definitely work. I thought of some kind of cyclone to shoot into but I would have to be able to back under it. Does anyone have any ideas?
(Dust Collection and Safety Equipment Forum)
From contributor G:
A cyclone is what you need. Elevate it with a metal or wood frame so you can back under it.
From Contributor O
The cyclone will work, but you need a rotary air lock under it so the shavings drop into the storage/trailer or other transport system. With no air lock, the shavings will blow at high velocity and be difficult to contain. Using an air lock is good practice because if you are exhausting to the outside in a closed building, you are putting a negative pressure in the building. This could draw heat combustion gases back down a flue and poison people in the building. If nothing else, it will compromise the free flow of the system. The air lock will allow the air to be returned to the building, equalizing the pressure and allowing air filtration at the same time. Your heated or A/C air will recycle, helping on energy costs. This has been general practice, and very basic since about 1960.
From contributor G:
The air from the cyclone has to be returned back to the building to equalize pressure. This is done with ductwork on the exhaust side of the cyclone ducting the air back into the shop. For this to work you need filter bags (a baghouse) between the cyclone and shop. The airlock, as Contributor O pointed out is also necessary.
From Contributor H
If this is all outside you can solve your problem with a vertical chimney pipe off the end of the trailer away from the shavings intake pipe. If you are using 8" dust pipe I would try a 12" diameter pipe running 6' to 8' high for starters. The idea is that the air flow out of this stack should move slower than the air flow into the trailer. As such it needs to be a larger pipe than the shavings pipe and needs to go high enough so that any chips that do head up can't reach the top and blow out. Since you are already blowing your chips outside you likely are not concerned about returning the air to the shop. I use a similar stack system on my indoor secondary blower for moving shavings into bags that are not directly under my cyclone's rotary air lock. I've also had outdoor trailers like yours in the past so know your problem first hand.
From Contributor J
Almost all small shop dust collectors and cyclones fail to provide good fine dust collection. They consistently do not move the air volumes or provide the fine filtering that decades of research by those firms that guarantee customer air quality show we must have to get good fine dust collection. Almost all small shop dust collectors only move enough air for good “chip collection” meaning picking up the chips and sawdust we would otherwise sweep up with a broom.