Page 231 - Industrial Power Engineering and Applications Handbook

8/21 0 Industrial Power Engineering and Applications Handbook

Table 8.5 Service Factors for flat and V-belts
Types of loads Types of driving units
Light starts Heavy starts direct on line
'Soft' starters, star-delta, wound motor
and A/T starters, or when the prime mover
is fitted with centrifugal clutches or
delayed-action fluid couplings
Class Examples Hours of duty per day Hours of duty per day
IO and Over 10 Over 16 10 and Over 10 Over 16
under to 16 under to 16

Class 1
(Light duty)
Agitators (uniform density)
Blowers, exhausts and fans 1 .o 1.1 1.2 1.1 1.2 1.3
(up to 75 kW)
Centrifugal compressors and pumps
Belt conveyors (uniformly loaded)
Class 2
(Medium duty)
Agitators and mixers (variable density)
Blowers, exhausts and fans (over 75 kW)
Rotary compressors and pumps (other
than centrifugal) 1.1 1.2 1.3 1.2 1.3 1.4
Belt conveyors (not uniformly loaded)
Generators and exciters
Laundry machinery
Line shafts
Machine tools
Printing machinery
Sawmill and woodworking machinery
Screens (rotary)
Class 3
(Heavy duty)
Brick machinery
Bucket elevators
Compressors and pumps (reciprocating) 1.2 1.3 1.4 1.4 1.5 1.6
Conveyors (heavy duty)
Hoists
Mills (hammer)
Pulverizers
Punches, presses, shears
Quarry plant
Rubber machinery
Screens (vibrating)
Textile machinery)
Class 4
(Extra heavy duty)
Crushers 1.3 1.4 1.5 1.5 1.6 1.8
For speed-increasing drives of speed ratio 1 .OO to 1.24: multiply service factor by 1 .OO
speed ratio 1.25 to 1.74: multiply service factor by 1.05
speed ratio 1.75 to 2.49: multiply service factor by 1.1 1
speed ratio 2.50 to 3.49: multiply service factor by 1.18
speed ratio 3.50 and over: multiply service factor by 1.25
Note
1 The service factors do not apply to light duty drives.
2 The use of a jockey (idler) pulley on the outside of the belt is not recommended.
Special conditions
For reversing drives, except where high torque is not present on starting, add 20% to these factors