On Wed, Jan 15, 2025 at 02:41 PM, imranindiana wrote:
You have the correct cross-section of 8” pipe (180 mm^2). If you know the maximum air speed in your system, you can linearly reduce it (by increasing baffle cross section) to achieve ~1500 FPM recommended by Michael.
The 1500 FPM recommendation (actually 8 m/s) comes from European standards for maximum airspeed in return air ducts.? It's too high of a number for baffles.? Mostly because baffles tend to be implemented where there's a chamber that allows the air to more or less come to a halt, and then you have very poor aerodynamics leading into the path of the baffle.? As such, 1500 FPM through the baffle probably imposes more back pressure than you'd want on the typical dust collector.? High pressure dust collectors like an Oneida High Vacuum collector or a Hocking Polytechnic Vacumobil MD 160 might not mind the extra back pressure.? For baffles, I'd stick with HVAC ducting air-speed limits, which I believe are about 600 FPM (as per ACCA manual D).? But of course a baffle is essentially a really crappy HVAC duct, so 300 FPM would be even better.
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Note that this implies a baffle with a cross section of several square feet, depending upon the CFM you think your collector is moving.? That flies in the face of people's instincts for baffles, where they want a small cross section because they fear letting more sound escape with a large cross section.? But the effectiveness of a baffle is all about forcing the sound waves to bounce off the sides of the baffle multiple times, combined with a good sound attenuating liner to the baffle, and large baffles work very well when done correctly.
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-Michael Wolf
Tahoe City, CA
