Which load type is classified as constant torque loads?

• A. Fans, centrifugal blowers, and centrifugal pumps
• B. Hoists, conveyors, mixers, and reciprocating or rotary compressors
• C. Wheel grinders, large driller machines, lathes, planers, and boring machines
• D. All of the above

Answer: (B)

Loads are categorized by how the torque they demand from the motor changes with speed. A constant torque load requires roughly the same torque across the speed range, so the motor’s torque stays about constant while power increases with speed.

Hoists, conveyors, mixers, and reciprocating or rotary compressors fit this pattern because the resisting torque they present to the drive is essentially constant over different speeds. You’re moving a fixed load or maintaining belt tension, agitation, or pressure, so the motor needs nearly the same torque whether you run slow or fast; the speed mainly affects how much power is delivered.

Centrifugal fans, blowers, and pumps behave differently: as speed increases, the resistance from the moving air or fluid grows more steeply, so the torque the motor must provide increases with speed, making this a variable torque load.

Machine tools like wheel grinders, large driller machines, lathes, planers, and boring machines are usually treated as constant horsepower loads, where the required power stays roughly constant but the torque drops as speed goes up.

Therefore, the set that includes hoists, conveyors, mixers, and reciprocating or rotary compressors represents constant torque loads.