Quieting Down a Dust Control System
Advice on fan selection, fan placement, and other factors that could affect the noise generated in a dust extraction system. December 31, 2012
Question
I have a noisy dust extraction system. Is there anything I can do to make it quieter?
Forum Responses
(Dust Collection and Safety Equipment Forum)
From contributor R:
I achieved good results from installing a duct silencer between my exterior cyclone and indoor bag house. It knocked off close to 15 db as measured inside. The system is still loud, but the cost was worth it for me and my employees. I purchased mine from Air Handling Systems.
From the original questioner:
I have an old extraction fan without a cyclone. Do you think a modern fan would decrease noise? What effect does a cyclone have on noise?
From contributor R:
“Do you think a modern fan would decrease noise? Straight blade radial fans are noisier than inclined blades or air foils. So a newer fan would probably help. But that is the extent of my experience.”
What effect does a cyclone have on noise? Not much, it will absorb/radiate a small fraction, but most of the noise is still in the exhaust airstream.
From the original questioner:
If I were to have a new quieter fan, would I need a cyclone to stop the heavier shavings and debris reaching and damaging the air foils in the fan? I'm not sure if a silencer would work on my system. According to Air Handling Systems their silencers can only be fitted on the outlet side of the fan and not the inlet side. My fan exhausts everything into a shed which is outside so unless the silencer will somehow stop the noise reverberating back through the ducting into my workshop, I don't think it will be suitable.
From contributor R:
Not necessarily. It depends on how much actual debris you have. Blocks of hardwood might dent an impeller, but these things are much more robust than the furnace type squirrel cage blowers. I work mostly solid wood, so we have a cyclone to drop into a dumpster, rather than use barrels or bags. I just remembered that there are now large blowers on the market designed to run at lower speeds.
From contributor K:
Sound is directional - so you may be able to decrease the noise by redirecting the discharge. Where is the sound most noticeable? Silencers require relatively clean air. It sounds like you have a material handling fan.
From the original questioner:
The sound seems to be the same everywhere in our workshop. The sound only increases when I go outside to the extraction fan. I'm looking at variable frequency drive for the extractor fan as I'm sure this will reduce the noise as well.
From contributor K:
If you're fan is on the push side of the collector, putting a quieter fan on the pull side would help. This would also be a more efficient fan. With it being on the material handling side, there's no way to dampen the sound without altering the airstream which would cause a maintenance nightmare. What HP is your fan? Do you return air back into facility? Has this fan always been loud?
From the original questioner:
The fan is on the push side of a cyclone which exhausts out of its top into the atmosphere. No, we don't return it back into our facility. The fan is rated at 25KW. It has always been loud.
From contributor K:
OK - my recommendation is remove the push fan (loud), and put a cleaner air fan on the pull sideYou may be able to put a top mounted fan directly on the cyclone (must have flange to mate with). Otherwise, duct to a concrete mounted fan. Since the sound generator is the fan, the sound power bands will need to pass through the cyclone which will then act as a muffler.
