IMPELLER DIRECTION

Did you know that a down-flow mixer and an up-flow mixer are not one in the same? Most mixers are designed to pump in only one direction of rotation.

A popular (albeit wrong) assumption is that one direction of rotation of a mixer impeller produces “down flow” mixing, and merely reversing direction of the motor and impeller causes “up-flow” mixing. In truth, a downward pumping mixer and an up-pumping mixer are unique and very separate machines. Design of shaft length, impeller and hub, and even motor and gearbox specification are all different considering application requirement for downward-flow verses upward-flow mixing.

Most (if not all) impellers are power and flow rated for one direction only. If an impeller is reversed by running the motor “backwards”, or the impeller is physically flipped upside down on the shaft, the overall efficiency and resulting pumping action is significantly altered. In certain applications, reversing flow over an impeller can be potentially dangerous and catastrophic, causing failure of the mixer shaft, motor, gearbox, and/or impeller.

Don’t assume. Always be on the lookout for impellers rotating or mounted in the wrong direction. Just because the impeller is spinning, doesn’t mean it’s properly mixing.