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Relationship of torque and shaft size

Plant Engineering
Publication date: 
April 2015
Chuck Yung, EASA Senior Technical Support Specialist

Have you ever wondered why various types of electric motors with the same horsepower/kilowatt ratings have different shaft diameters, or why some pump shafts are so much smaller than the shafts of the motors that drive them? And what about those hollow-shaft motors? A rudimentary understanding of how shaft sizes are determined can be helpful to anyone who works with pumps, fans, elevators or any other motor-driven equipment.

Engineers often design using an ample safety factor, but consider modifying a shaft only with good engineering support. The greater the consequence of failure, the more generous the safety factor should be.