Shaft Torque, Critical Speed, and Retrofitting

Another consideration is the shaft torque. Since impellers of the same diameter require the same power input to achieve the same blend time, an impeller with a lower power number will have to operate at a higher speed and hence will have a lower shaft torque (P = 2ttNA). Since the size of the shaft and gearbox are related to the torque, reducing the torque may reduce the agitator size and reduce the cost 

One factor to be aware of when making this decision is the critical speed of the shaft and impeller assembly. Running at a higher speed may reduce the torque, but the agitator may require a larger shaft anyway because the operating speed is 

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