12.20 Overload factor

The overload factor Ko makes allowance for the externally applied loads which are in excess of the nominal tangential load, Wt. Overload factors can only be established after considerable field experience is gained in a particular application. For an overload factor of unity, this rating mehtod includes the capacity to sustain a limited number of up to 200% momentary overload cycles (typically less than four starts 8 hours, with a peak not exceeding one second duration). Higher or more frequent momentary overloads shall be considered separately. In determining the overload factor, consideration should be given to the fact that many prime movers and driven equipment, individually or in combination, develop momentarypeak torques appreciably greater than those determined by the nominal ratings of either the prime mover or the driven equipment. There are many possible sources of overload which should be considered. Some of these are: system vibrations, acceleration torques, overspeeds, varitions in system operation, split path load sharing among multiple prime movers, and changes in process load conditions.

Examples of operating characteristics of driving machines:

Examples of operating characteristics of driving machines:






Operating Characteristics of Driven Machine
Operating Characteristics
of Driving Machine uniformlight shockmedium shockheavy shock





uniform 1.00 1.25 1.50 1.75
light shock 1.10 1.35 1.60 1.85
medium shock 1.25 1.50 1.75 2.00
heavy shock 1.50 1.75 2.00 2.25