V belts are common power transmission belts manufactured in a V-like shape. This specific geometry is ideal for industrial applications, as it allows belts to be wedged into a pulley system for extra traction. Also known as V-belts or Vee Belts, this design transmits power from motors to driven mechanisms.
V belts are available in various sizes, with classic and narrow models needed for different types of equipment. Narrow units have a greater depth-to-width ratio, making them ideal for high-speed applications. Along with size, V belts also differ in their design. There are cogged units with a notched structure, wrapped and banded models, and linked designs for specialised applications. All of these belts are run on V-shaped pulleys without teeth.
In this article, we’ll help you understand V belt sizes and configurations. We’ll tell you how to measure a V belt and avoid sizing mistakes when ordering. For additional information on V belt sizes and applications, contact our team.
What is a V-belt, and how does it work?
A V belt, also known as a friction drive, is a transmission belt used in various machinery, including automotive, industrial, and agricultural applications. It is designed to transmit power or torque from the driving component to the driven component, providing a secure and efficient way to transmit power.
The V belt’s design facilitates gripping onto the roller components (i.e., pulleys) during operation, decreasing the risk of slippage and increasing the consistency of the system’s output.
A standard wrapped V belt consists of a rubber or synthetic material body, a fabric or cord reinforcement, and a wrap or cover. The wrap or cover is designed to grip the pulleys and transmit power, while the fabric or cord reinforcement provides additional strength and durability. The rubber or synthetic material body provides flexibility and resistance to wear.
This combination of materials ensures the V belt can handle the operation stresses while maintaining a long service life.
V belt sizes and applications
Before we analyse different V drive belt sizes, it’s important to understand why variations exist. Many belt sizes are needed to accommodate various machinery types and applications.
Industrial equipment varies considerably in design, with standards also affected by the age and origin of machinery. Whether building something new, repurposing existing technology, or repairing a classic unit, it’s important to size V belts carefully.
If you have an old V belt, it can be helpful to use it as a reference to ensure accurate sizing for your new belt.
Overview of V belt sizing standards
Sizing V belts properly can be confusing. Along with the many sizes available, there are also different measuring systems worldwide. To move forward with clarity, it’s important to understand the following length measurements:
- Outside belt length: This measurement describes the outer circumference of the belt, typically without tension. The external length is often used, but it’s not always valid. Some belts have an arched top, while others are flat, which leads to incompatible readings.
- Inside belt length: This length is measured with flat pulleys and a tape measure. Similar to outside length, this measurement suffers from design variations by different manufacturers. However, knowing the diameter and centre of the pulleys can be helpful.
- Belt pitch length: Also known as the datum length, this describes the pitch diameter of the sheaves used. Industrial belts are often specified in these terms, with the pitch circumference of one sheave added to twice the centre distance between two equal-diameter sheaves. This shared measurement includes traditional belt pitch lines and modern datum diameters or datum lengths.
- Belt effective length: This length describes the outside diameter of a sheave at a specified tension. RMA, ASAE, or SAE standards specify the groove top width dimension used. This length is obtained by adding the effective outside circumference of one sheave to twice the centre distance between the standard measuring sheaves.
- Nominal belt length: This measurement refers to the length and cross-section of a specific belt. The nominal length is widely used as a product identifier. For example, an A38 has a nominal length of 38 inches, and a 4L440 has a nominal length of 44.0 inches.
How V belts are measured
Measuring V belts accurately can be a complex procedure. While the process isn’t difficult, understanding what to measure and how to combine data can seem complicated.
There are various factors to consider, such as belt length, belt width, and belt angles. Power transmission belts also come in a number of profiles, including M, Z, A, B, C, D, and E.
To make things even more complicated, the notched versions of these belts are referred to as ZX, AX, BX, and CX. While these belts have the same dimensions as standard wrapped belts, they also have cogging running perpendicular to the length.
How to size V belts in 5 easy steps
The following steps are useful if you’re measuring V belt length without an existing unit to compare:
- Wrap nylon rope or a similar material around both pulleys, overlapping around 10-15 cm.
- Draw a line across the rope with a permanent marker, ensuring it crosses both sections.
- Lay the marked rope down on a large, flat surface.
- Measure the distance between the two marks with a tape measure.
- This measurement will determine the circumference of the new V belt.
How do you measure belt size? Potential issues
While this process is relatively straightforward, there are some issues to consider. First and foremost, it’s essential to understand the difference between external and internal circumferences, as mentioned above. While brands like Gates, Opti, and Carlisle use an internal circumference listed in inches, others use an external measurement.
Gates Belts identification data »
You can change external to internal dimensions if needed. Deduct the following lengths based on these unit codes: Z – 1 inch, A – 2 inches, B – 3 inches, C – 4 inches, D – 5 inches, and E – 6 inches. Many imperial belts align inside circumference measurements with their product code. For example, a 3V400 has an internal circumference of 40.0 inches, and a 3V450 has an internal circumference of 40.5 inches.
Narrow section V belts are identified by their pitch length, which is different from the external or internal circumference. To calculate the pitch length of the belt, you must add a length to the inside circumference based on these unit codes: SPZ – 13 mm, SPA – 18 mm, SPB – 22 mm, and SPC – 30 mm.
How to ensure correct belt sizing
Industrial equipment relies on precision. Slight variations in sizing can drastically impact performance, affecting everything from equipment durability and longevity to compliance and worker safety. When buying new V belts or upgrading existing units, it’s vital to get your measurements correct. Use an existing belt for comparison if possible, and use the steps above to size units correctly before making an order. The best advice, however, is also the oldest: measure everything twice to avoid making mistakes.
To ensure 100% accuracy, talk to the professionals at Statewide Bearings. We are a trusted supplier of bearings and V belts for industrial applications. We have an extensive range of products and services, from lubrication and power transmission components to pumps and associated products.
We offer friendly advice before and after the sale, and we deliver practical solutions in a cost-effective package. Please get in touch with our team to learn more.
