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thanks to Mike and Jeffrey for responses.
I was at an auction over the weekend. There were many many fan assemblies available that went incredibly cheap (under $10).
Now, assuming I can pick one that has a good motor and bearings, how would one pick an appropriate fan?
Based on discussions in Part 1, I know to avoid a squirrel cage fan. So I am looking only at fans with blades.
Are there tricks to the dimensions, sizing, etc? Or do I just grab one that has at least a 1.5 – 2 HP motor?
Thanks,
Joe
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Joe,
Dust collection fans are usually made with straight radial blades. In other words, the blades point straight outwards from the center bearing of the impeller. These types of fans exhibit higher static pressure ratings, and lower efficiency than other types of fans. However, they excel at moving material (ie wood dust & chips, metal chips, etc).
Next to look for would be backward curved blades. On a backward-curved type fan, the impeller rotates towards the fan discharge opening, but the blades tilt away from the opening. Backward -curved fans generally have higher pressure ratings than forward curved fans. These fans are usually used for ventilation systems, but may be adaptable to a home-made dust collection system. They aren't designed for dust collection, but if you can find one for $10, it may be worth a try...!!
Lastly, you may come accross forward-curved bladed fans. The blades are cupped toward the fan discarge opening. Squirrel cage fans are usually of this type, and are designed for low pressure ventilation systems, like home furnaces/air conditioners. You might be able to get one of these fans to work for dust collection, but you would have to make some design compromises, like shorter runs of pipe and fewer elbows (and still might not work well).
As far as sizing, you can't tell just by looking at a fan exactly how many CFM it will move, and at what static pressure. You may get lucky and find a nameplate, which helps! However, you really need to look at performance curves or rating charts. If you can get the fan model number off of the nameplate, you can try calling the manufacturer to get the info you need.
In general, if you find a fan with a 1-2 HP motor, you may be in the ball park, but it totally depends on the fan construction and on the pressure drop of your system. If you are only spending $10 bucks, and you have a lot of time to tinker and trouble shoot, just give the 1-2 HP a try and see if it works.
If time is your limiting factor, I would suggest buying a factory-made system, since you would have technical assistance with fan selection and troubleshooting.
Good luck,
Jay
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