Exhaust principles and Particle collection

Fume Extraction Verses Particle Extraction

So first off let's get this little problem out of the way, if you have an exhaust fan or filter system with an say 6-inch inlet and outlet, then increasing the size of the ducting is NOT and I REPEAT NOT!!!! going to do anything but reduce your FPM (Feet Per Minute). When you design your system remember this, you can reduce to speed up the airflow but at any point past that point will not gain anything by going big again. So Large to small never Small to Large

Coming from a woodworking background I have come to realize that a very important distinction is missing from the Laser Engraving world when it comes to exhaust systems. I could make this a very long post but to put it very simply;

A Fume Extractor is designed to move gases it uses the highest CFM possible to remove as much of the gasses from the area as quickly as possible.

A Particle Extractor on the other hand is designed to move the particles, Dust, metal shavings ect from the area using FPM or localized suction.

These two are very different in the function of how they work, This article is going to discuss my idea on how to deal with the issues that spring up from needing to combine the two.


Lasers produce both fumes and particles this is true for both Fiber and Co2 and because the Particles are heavier than air you have to keep your FPM high enough to move those particles through the system or create a collector at strategic points in the system to limit the buildup of those particles in the line. These collectors can also become very important if you use a fiber machine to work with precious metals as they will collect the Silver or gold dust being removed,

One of the ways this can be done is to create a drop out in your line. They are easy to make and should be mounted before your feed line connects into the main line as close as possible to the machine in question. A relatively cheap way of doing this is to take an 8 inch or better 12inch PVC Pipe plug the top, and on the bottom use a removable plug that can be removed as a cleanout, drill a hole for the outlet on top and an inlet about halfway down. When the fast air from the laser moves into the larger diameter tube it will slow down and allow the particles to drop down into the collection bowl. The Fumes will continue to be exhausted out to the filter media or into the open.

Key Points for your exhaust system.

  1. If you are using multiple channels then your main line needs to be as large as possible this will help keep your maximum CFM the blower will produce throughout the system, that being said, do not waste your money on an 8inch pipe if the inlet to your exhaust is an 6inch, you are not going to gain anything and will lose your FPM. 
  2. Remember air is like water, sharp turns and elbows will interrupt the flow of the air and moving from a large to small will increase the speed of the air and vice versa
  3. A line that runs straight across then straight up is going to be a choke point for particles and a drop out collection system should be mounted at this junction to allow for easy clean out.
  4. If you need to increase the FPM at the machine then use a smaller line i.e. reduce from a six down to a four this will increase the suction at the machine allowing the dust to be pulled into the system, but again where that small line goes into the larger the FPM will drop, Use the example above at the reduction point to collect the particles.
  5. If you are using a fume extractor with filter media, then the above example of a drop out can save you hundreds of dollars simply by removing the large particles reducing the amount of the particles reaching the filter medial.
  6. Cleanouts or dropouts can be very important if you work with acrylic as the dust from engraving acrylic is flammable.
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