The laser engraver had two size options, 3 or 4″ dia., for its two exhaust ports. We opted for the larger one to maximize the gas flow.
One port is for the fume exiting from the top of the table. The other port connected to the bottom center of the lasing table. This is for fume extraction purpose as well as sucking the materials flat while lasing.
This meant that it required a decent amount of negative pressure to vacuum down 1/4″ plywood.
Our original design used an inline fan and/or a centrifugal fan from “shop fan.” These just didn’t create enough negative pressures to suck the materials flat as we wished. But while trying, we learned to minimize the flow resistance as much as possible using varieties of techniques and common senses.
This unit also act as a mixing unit for the two incoming ports as the concentrations of fume could be quite different depending on how much the blast gate is opened for the top port.
- Think like a gas molecule (think like a Japanese commuter during a rush-hour)
- Use larger diameter ducts
- Minimize number of turns
- Maximize the diameter of turns.
- Avoid turns and other changes in diameters prior to flow disturbances like a wye, a filter, noise suppression canister or a fan
- Keep interiors as smooth as possible
- Think about laminar flow
- Minimize the use of flexible (PVC or corrugated aluminum) ducts
- Employ veins to turn and guide the exhaust
- Use a more powerful centrifugal fan
- Use pressure gauge to compare design changes
- Keep filters clean
- Use appropriate sized activated charcoal pellets
- Minimize the back and forth changes in the gas velocity*
*Does this matter in compressible fluid dynamics?
How to Reduce Exhaust Leakage
The exhaust system is designed to pull the fumes out, keeping the negative pressure as much as possible throughout . This, by design, limits any fumes leaking out during any point of filtration and movement of the fumes. For an example, if a fan were to be placed between the laser engraver and the filtration system, any gas flow after the fan will have positive pressure, causing any gaps in the filtration system’s enclosure to leak out the exhaust, which will include carbon monoxide and other harmful vapors.
By keeping the fan at the very end of the system (right before it exits the building) ensures minimal exhaust leakage.
Hot-glue, silicone, foam gaskets, metal & fabric HVAC duct tapes and blue masking tapes are used extensively throughout the design to minimize leaks and improve efficiencies of the fume extraction process.