SEED Guides Clutches Requirements <

3.5 Duty
The duty of a clutch affects the specification because it measures how frequently the device is used and how often it is forced to perform near its design limits. By considering the duty of a device, a service factor can be assigned. The service factor essentially causes the component to be oversized and therefore more robust for the application. Generally, the design power is increased. The values of service factors are usually quoted by manufacturers against various applications and duties. A general table of factors is given below. Some of the values given are relatively large in comparison to those for use with motors, couplings etc. The reason for this is that clutches, especially the friction type, are subjected to very large shock loads and transients.

General System Description
Typical Driven Systems
Type of Driver
Small Electric Motors, Turbines
Internal Combustion Engines, 4-6 Cylinders, Medium to large Electric Motors
Internal Combustion Engines 2-3 Cylinders
One Cylinder Source

Steady power source, steady load, no shock or overload.
Steady power source. Some irregularity of load up to 1.5 times nomal power.
Belt drives, small generators, centrifugal pumps, fans, machine tools.
1.5
1.7
1.9
2.2
Small elevators, light machinery for wood, metal and textiles. Conveyor belts.
1.8
2.0
2.4
2.7
Heavy load elevators, larger conveyor belts, larger machines, reciprocating pumps.
2.0
2.2
2.4
2.7
Frequent start and stop, overloads, cycling, high inertia starts, high whip start, high power, pulsating power source.
Presses, shears, punches, piston pumps, hammer mills, cranes and hoists.
2.5
2.7
2.9
3.2
Stone crushers, roll mills, heavy mixers, single cylinder compressors.
3.0
3.2
3.4
3.7