Explaining V-Belt Drive Misalignment

by Don R. Sullivan

V-belt drive misalignment exists when the driver and driven sheaves are not properly aligned. Misalignment can take either the form of angular or parallel (offset) misalignment, or a combination of both.


Figure 2. Parallel misalignment.
Angular misalignment occurs when the faces of the sheaves do not form a straight line. (See Figure 1.)

With parallel misalignment, the sheaves may be in angular alignment, but their position on the shaft creates a parallel offset. (See Figure 2.)

Ideally, you want to have both parallel and angular harmony. The objective is to have the shafts parallel and the center lines of the two sheaves in line with each other. (See Figure 3.)

IMPACTS OF V-BELT MISALIGNMENT

Figure 3. Desired alignment.
Excessive V-belt drive misalignment causes one or more of the following drive conditions:

1. Premature V-belt failure.

2. Uneven and premature sheave wear.

3. Higher V-belt operating temperature and energy consumption.

4. Uneven wear on belt sidewall.

5. V-belts rolling over in the sheave groove.

6. Transfer of load to one side of the V-belt, which can destroy the belt cords on that side.

7. Increased probability of vibration.

8. Drive instability.


BEST PRACTICES FOR V-BELT DRIVE ALIGNMENT

Acceptable V-belt misalignment for raw edge cogged V-belts is 1/2° or 1/10 inch per foot of center distance. Non-cogged V-belts can tolerate sheave misalignment of about 2° maximum.

The easiest way to quickly ensure sheave alignment is to use a straight edge or multi point contact string method.

Special Note: Sheave alignment should be checked before and after belt tensioning. Always adhere to strict safety and lock out and tag out procedures when performing maintenance on a V-belt drive.

V-Belt Drive Video 

An informative V-belt drive sheave installation and tensioning instructional video