Could someone explain the difference in impeller size?

[Jim Andrew]

Was looking at the Grizzly site, their 3hp cyclone has a 15 1/2" impeller, but their 2 cartridge 3hp dust collector has a 12 3/4" impeller. Seems a lot of difference. Can someone explain the difference? I recently bought a dustcop 3hp cyclone, thinking it would have more cfm than my 2hp woodsucker, but the dustkop has only a 12 1/2" straight blade impeller, it is a blow through design, and the woodsucker has the blower on top, like the clearvue, and has a 13 1/4" cyclone, so I figured the dustkop doesn't have more cfm's than the woodsucker. Can someone elaborate on the 2 systems?

[David Kumm]

A straight blade impeller will usually be a smaller diameter for a given Hp than a curved blade design. The straight blade is less efficient at low static pressure and will deliver less cfm but as the pressure goes up, the straight blade will deliver more while a curved blade will top out and even more speed won't deliver much more air. Commerical units that are either professionally designed or older often have the straight blade. Louder and must be engineered for the proper pipe to restrict it so it is more efficient and doesn't overamp the motor. A straight blade will deliver more cfm if speeded up provided you have enough amps. I run a 15.75" straight blade with a 7.5 hp motor and 8" reduced to 7" mains. Had I run 9" and 8" mains I could have used a 17" curved blade. I believe that Oneida runs a straight blade in their smart collector that automatically adjusts cfm and speed. A straight blade is the only design approved for material pass through so it is used on a push through system. If your ducts are a little small, runs are long, or machine ports are small and restrictive, the straight blade may deliver more useable cfm. Dave

[Michael W. Clark]

Impeller diameter is often an indication of the static pressure capability of the fan. The larger the diameter, the higher the SP capability (generally as I am sure there are exceptions). The radial blade is less efficient than a radial tip which is less efficient than a backward inclined. Radial wheels are best when handling particulate, especially on the dirty side of the collector. Your Grizzly cyclone has more pressure drop than the bagger style, so a larger impellor may have been specified to account for this. The Woodsucker and Dustkop are close, but it could be the same idea.

Mike