Figure 1: V-belt
A v-belt is a rubber belt with a trapezoidal cross-section used for driving mechanisms in an engine, such as fans and pumps. When a v-belt gets worn out, it is difficult to determine the type and dimensions of the belt to find a proper replacement. This article discusses finding a v-belt’s original type, length, and width and how to install a replacement belt.
A well-designed and properly aligned v-belt drive is highly efficient. Over time, though, maintenance and installation factors (e.g., misalignment, tension, and worn-out sheaves) negatively affect the v-belt’s effectiveness. Often, high loads and high temperatures contribute to v-belt failure. Hence, it is essential to inspect a v-belt for possible failure and replace it if needed.
To identify a v-belt, read the part number on the v-belt if the branding is still intact. However, after many hours of use, the label may be worn out and may not be legible to read. In this case, it is essential to find out the belt's original dimensions, as discussed below, to find a proper replacement.
Figure 2: Part number labeled on a v-belt.
A v-belt is characterized by its top width and depth, as seen in Figure 3. For example, a top width of 7/8” and a depth of 17/32” is a “C” belt, as seen in Table 1. Use the identification chart given in Table 1 to know each type of v-belt’s top width and depth.
|V-Belt Type||Top width (mm / in)||Depth (in inch)|
|3L||9.5 / 3/8||5.6 / 7/32|
|4L||12.7 / 1/2||7.9 / 5/16|
|5L||16.7 / 21/32||9.5 / 3/8|
|A||12.7 / 1/2||7.9 / 5/16|
|B||16.7 / 21/32||11.1 / 7/16|
|C||22.2 / 7/8||13.5 / 17/32|
|3V||9.5 / 3/8||7.9 / 5/16|
|5V||15.9 / 5/8||13.5 / 17/32|
|8V||25.4 / 1||23.0 / 29/32|
Table 1: Identification chart for v-belt types
Regardless of the type of v-belt, use the following measurements to find a proper replacement for it:
Use v-belt measuring tools (e.g., hard ruler, hard tape measure, or soft tape measure)to perform the following steps and determine the length, top width and depth of the v-belt:
The depth and top width: Measure across the top across the top of the tape to get the width of the belt (Figure 3 labeled A) and measure the straight distance across the cross-section to get the depth (Figure 3 labeled B). This means that the user needs to measure the widest part of the belt (thick section) for the width and then measure down from the widest part to the narrowest part of the belt for the depth.
Figure 3: Top width (A) and depth (B) of a v-belt.
Figure 4: Inner length of a v-belt (A) and outer length of a v-belt (B)
Value (in inches) to be added to the belt number
|v-belt part number||Outer length (in inches)|
Table 2: Relation between the outer and inner circumference of each belt type
Use the following v-belt measurement tools to determine the belt’s outer circumference.
Note: Once the outer circumference is measured, use the values given in Table 2 to calculate the inner circumference of each belt type to designate the v-belt correctly.
If the belt is attached to a pulley, tie a string around the belt on the pulley and measure the length of this string to get an estimate of the belt’s length. If there is no belt attached to the pulley, tie the string on the inside part of the pulley to take the measurement, which estimates the belt’s inner length.
This example uses a v-belt, with a worn out label, that needs replacement. Perform the following steps to identify the belt type correctly:
Perform the following steps to install a v-belt on a pulley drive:
Note: It is important to use a set of all new belts, preferably of the same brand. Also, do not mix different v-belt constructions (like banded, raw edge, and cogged). Using a combination of old and new belts can lead to a few issues:
V-belts act as transmission belts. Driving mechanisms in an engine, such as fans and pumps, use v-belts.
Prevent v-belt slips by adjusting its tension and changing worn-out pulleys.