Constant Torque, Constant HP and Variable Torque

 

Constant Torque

• The constant torque remains constant regardless of operating speed. However, HP of motor varies directly with speed.

       T = HP / N

       Where N = Speed in RPM

Examples 

• Compressors
• Conveyors
• Hoists
• Positive displacement pumps

Constant HP

• The motor torque remains constant below its normal speed and its value decreases above normal speed. 
• The HP remains fairly constant above normal speed.   
• Lathe machine requires slow speed for deep cut and high speed for finish cut, drill press, milling machine

Variable Torque

• Many types of load requires low torque when it is driven below rated speed of the load conversely such load may requires higher torque when driven above rated speed of the load. 
• The variable torque varies as the square of the speed and horse power varies as the cube of speed.

      T α N²

      HP α N³

     Where N = Speed in RPM

Examples

• Centrifugal pumps
• Fans
• Compressors

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