V-belts types and dimensions
V-belts are power transmission elements that use friction between their trapezoidal flanks and grooved pulleys to transfer motion between shafts. Their wedge-shaped cross-section allows transmitting up to 500 kW / 670 hp of power in industrial configurations, operating in a temperature range of –35 to 85 °C / –31 to 185 °F with a typical mechanical efficiency of 95 %.
Compared to flat belts, V-belts multiply the traction capacity thanks to the wedging effect in the pulley groove, which increases the effective friction force by a factor of 3 to 5 for the same coefficient of friction.
Types and standard designations
Section titled “Types and standard designations”Classic V-belts are identified by letters according to ISO 4184 and ASME B16.1 standards, with standard cross-section dimensions in inches.
| Designation | Series | Typical application |
|---|---|---|
| A | Classic belt | Household appliances, fans, small pumps |
| B | Classic belt | Conveyors, compressors, agricultural machinery |
| C | Classic belt | Crushers, sludge pumps, heavy drives |
| D | Classic belt | Ball mills, presses, large fans |
| 3V | Narrow wedge belt | Compact high-speed drives |
| 5V | Narrow wedge belt | Centrifugal pumps, generators, industrial transmissions |
| 8V | Narrow wedge belt | Large fans, compressors, mining equipment |
Designations A, B, C and D correspond to the classic section; series 3V, 5V and 8V belong to the narrow wedge belt family, which offer greater power capacity per unit width and allow smaller diameter pulleys.
Standard dimensions
Section titled “Standard dimensions”The geometry of each profile is defined by the top width (W), height (H) and flank angle (38° to 40° at rest). Pitch lengths are specified in millimeters for the metric series and in inches for the inch series.
| Type | Top width (W) | Height (H) | Flank angle |
|---|---|---|---|
| A | 12,7 mm / 1/2 in | 7,9 mm / 5/16 in | 40° |
| B | 16,7 mm / 21/32 in | 10,3 mm / 13/32 in | 40° |
| C | 22,2 mm / 7/8 in | 13,5 mm / 17/32 in | 40° |
| D | 31,8 mm / 1-1/4 in | 19,1 mm / 3/4 in | 40° |
| 3V | 9,5 mm / 3/8 in | 8,0 mm / 5/16 in | 40° |
| 5V | 15,9 mm / 5/8 in | 13,5 mm / 17/32 in | 40° |
| 8V | 25,4 mm / 1 in | 22,2 mm / 7/8 in | 40° |
Available lengths vary by manufacturer, ranging from 600 mm / 23.6 in (type A) up to more than 20 000 mm / 787 in (type D).
Materials
Section titled “Materials”The tensile core is formed by polyester or aramid fiber cables embedded in a synthetic rubber matrix with textile reinforcement on the flanks to resist abrasion. Belts for oily environments or extreme temperatures use chloroprene (Neoprene) or ethylene‑propylene (EPDM) compounds.
| Component | Predominant material | Main function |
|---|---|---|
| Tensile cord | High-tenacity polyester | Support the tensile load |
| Elastomeric core | Styrene‑butadiene rubber (SBR) | Transmit shear stress in the wedge |
| Side cover | Impregnated cotton fabric | Wear and heat resistance |
| Optional reinforcement | Aramid fiber | Reduce elongation in shock applications |
Load capacities
Section titled “Load capacities”The transmissible power per belt depends on the linear speed, the smaller pulley diameter and the service factor. For a type B belt running at 1750 rpm with a drive pulley of 150 mm / 5.9 in diameter, the basic capacity is approximately 5,5 kW / 7.4 hp per belt.
| Type | Power per belt at 1750 rpm (kW / hp) | Maximum recommended torque (Nm / lb·ft) |
|---|---|---|
| A | 2,2 kW / 3.0 hp | 12 Nm / 8.9 lb·ft |
| B | 5,5 kW / 7.4 hp | 30 Nm / 22.1 lb·ft |
| C | 14,9 kW / 20.0 hp | 81 Nm / 59.7 lb·ft |
| D | 37,3 kW / 50.0 hp | 203 Nm / 149.7 lb·ft |
| 5V | 18,6 kW / 25.0 hp | 102 Nm / 75.2 lb·ft |
Values correspond to standard conditions (contact arc 180°, uniform load, pulley of minimum recommended diameter). For real applications multiply by the length correction factor and the contact arc factor.
Selection criteria
Section titled “Selection criteria”The minimum pulley diameter is the first parameter that determines the appropriate belt section, since it directly influences service life due to bending fatigue.
| Type | Minimum pulley diameter (mm / in) |
|---|---|
| A | 76 mm / 3.0 in |
| B | 137 mm / 5.4 in |
| C | 229 mm / 9.0 in |
| D | 330 mm / 13.0 in |
| 3V | 63 mm / 2.5 in |
| 5V | 140 mm / 5.5 in |
| 8V | 315 mm / 12.4 in |
The selection procedure follows ISO 5292 or RMA IP‑20: (1) calculate the design power multiplying the nominal power by the service factor, (2) choose the belt section based on the design power and the fast shaft rpm, (3) determine the pulley diameters and center distance, (4) verify the linear speed (maximum 30 m/s / 5900 fpm for classic belts), (5) calculate the number of belts required.
Selection by application
Section titled “Selection by application”The following table guides the profile choice according to the machine type and typical required power.
| Application | Typical power (kW / hp) | Recommended profile | Main reason |
|---|---|---|---|
| Domestic axial fan | 0,37 kW / 0.5 hp | A | Low cost and small pulleys |
| Piston compressor | 5,5 kW / 7.5 hp | B | Resistance to pulsating loads |
| Belt conveyor | 15 kW / 20 hp | C | High traction capacity |
| Jaw crusher | 45 kW / 60 hp | D | Moderate shock transmission |
| Industrial centrifugal pump | 90 kW / 120 hp | 5V | High speed and compactness |
| Mine exhaust fan | 250 kW / 335 hp | 8V | High power in limited space |
In systems with contact arc below 160°, the number of belts must be increased by 20 %. Flat idler pulleys are preferably installed on the slack side and on the outside of the belt so as not to reduce the wrap angle on the smaller pulley.
Installation and alignment
Section titled “Installation and alignment”Angular alignment between pulleys must not exceed 1 mm / 0.039 in per 100 mm / 3.94 in of center distance. Installation tension is adjusted by the belt deflection under a given load; for example, for a profile B with center distance of 500 mm / 19.7 in, the deflection force must be 20–25 N / 4.5–5.6 lbf to obtain a 1 % elongation.
When installing a new belt, never force it with levers over the pulley, as the tensile cords are damaged. It is recommended to move the motor on its sliding base to reduce the center distance during installation and then tension.
Common failures and solutions
Section titled “Common failures and solutions”| Symptom | Probable cause | Solution |
|---|---|---|
| Cracks at the V base | Pulley diameter below minimum | Increase diameter or change to narrow profile |
| Excessive side wear | Angular misalignment or worn pulley | Realign shafts and replace pulley |
| Tensile rupture | Overload or violent impact | Reduce load or install torque limiter |
| Squealing at start-up | Insufficient tension or polished pulley | Tension per standard or regroove the groove |
| Abnormal vibration | Eccentric pulley or belt with length defect | Balance pulleys and replace belt |
Frequently Asked Questions (FAQ)
Section titled “Frequently Asked Questions (FAQ)”What maximum temperature does a standard V-belt withstand?
Section titled “What maximum temperature does a standard V-belt withstand?”The continuous service temperature for SBR belts is limited to 85 °C / 185 °F. EPDM formulations reach up to 120 °C / 248 °F intermittently.
How many belts can be mounted on the same pulley?
Section titled “How many belts can be mounted on the same pulley?”On standard pulleys up to 12 grooves for profiles A and B, 10 for C, and 8 for D are allowed, maintaining a length difference between belts of the same set below 0.2 %.
How often should a V-belt drive be retensioned?
Section titled “How often should a V-belt drive be retensioned?”It is recommended to check tension after the first 24 hours of operation and then every 500 hours or three months, whichever occurs first. Most belts lose up to 3 % of their length during initial seating.
Is it possible to replace a classic belt with a narrow one?
Section titled “Is it possible to replace a classic belt with a narrow one?”Yes, a 5V belt can replace a B belt in many applications, provided the pulleys have the same groove width. The narrow belt transmits up to 50 % more power in the same space.
What efficiency does a well-maintained V-belt drive have?
Section titled “What efficiency does a well-maintained V-belt drive have?”Mechanical efficiency ranges between 92 % and 98 %, with a typical value of 95 % when the load is stable and the linear speed does not exceed 20 m/s / 3937 fpm.
How is the length of a V-belt measured?
Section titled “How is the length of a V-belt measured?”The pitch length is measured at the height of the neutral axis of the tensile cord. An A‑40 belt has a pitch length of 1016 mm / 40 in. The actual measurement over the back of the belt is approximately 1.5 % greater.
References
Section titled “References”- engineeringtoolbox.com: https://www.engineeringtoolbox.com/pulley-motor-speed-d_1475.html
- mcmaster.com: https://www.mcmaster.com/products/v-belts/