Page 92 - Intro Predictive Maintenance

Machine-Train Monitoring Parameters 83

Figure 5–3 Double-reduction gearbox.

If the input speed is 1,800 rotations per minute (rpm), then the intermediate and output
speeds are calculated using the following:

¥
Input Speed Number of Input Gear Teeth
Intermediate Speed =
Number of Intermedia Gear Teeth
¥
Intermediate Speed Number of Intermediate Gear Teeth
Output Speed =
Number of Output Gear Teeth

5.2.4 V-Belts
V-belts are common intermediate drives for fans, blowers, and other types of machin-
ery. Unlike some other power-transmission mechanisms, V-belts generate unique
forcing functions that must be understood and evaluated as part of a vibration analy-
sis. The key monitoring parameters for V-belt–driven machinery are fault frequency
and running speed.

Most of the forcing functions generated by V-belt drives can be attributed to the
elastic or rubberband effect of the belt material. This elasticity is needed to pro-
vide the traction required to transmit power from the drive sheave (i.e., pulley) to
the driven sheave. Elasticity causes belts to act like springs, increasing vibration in
the direction of belt wrap, but damping it in the opposite direction. As a result,