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Problems finding the right belt?

If you have the belt previously used, where possible, record the old belt number written on the exposed top-surface of the belt. This is your best reference to find the original size, type, and length of the belt. If a search of our site does not provide a suitable result for this number, please contact us and we will refer to our large data base in order to help.

Check your old/worn/broken belt for any reference numbers. If you can't find a match by a search of our website, let us know and we will check against our data bases.

If there is NOT a product reference code remaining on the original belt, the correct belt may be found if you inform us of the machine brand and model, but there are some simple steps which you can take to identify a suitable replacement belt yourself.

 

Measuring your old V-belt.

Length:-

Specifying the length of a belt can be confusing. We normally recommend using the outside length; although the terms "effective outside-length", "inside", "pitch" and "nominal" length are also commonly quoted for different measurements of length.

Outside Belt Length:

The outside length of a belt can easily be measured with a tape under no tension. Please consider that some belts have an arched top whereas others have a flat top surface. This would result in different readings for two different belts, which were actually the same length.

A belt's outside length can also be measured by marking a start/finish point on the belt, and carefully rolling the belt along a clean, flat surface and placing two corresponding marks; the length can then be measured off with a steel tape measure.

If your old belt has a frayed breakage, it may be taped together for the purpose of measuring, as described above.

If the old belt has snapped with a clean-edged break, it may simply be measured by being pulled straight against a flat surface and measure.

The outside length of a belt may also be derived or checked by studying the geometry of the mechanical pulley arrangement - remember that this measurement should be derived from the outside diameters of the pulleys (at the top of each pulley's v-section) and NOT by placing a string-measure in the "valleys" of the pulleys.

To measure a v-belt that is still on the machine, unwind a length of non-stretch string and wrap it around the length of the belt surrounding the pulleys. When the string wraps around the entire circumference of the belt, use a marker to clearly mark the end as it meets the beginning portion. This allows for less room in measuring errors. Align the string with a tape measure across a flat surface, pulling tightly on the string so that it runs smoothly across the length of the tape.

V-Belt Section size (top-width & depth):-

Belt and pully section

Inspection:-

Inspect the existing belt, motor, fan and pulleys etc. Make sure the bearings, shafts and set screws are in good condition and secure.
Before measuring the section of the old belt, check to see the original belt’s section fits in to the pulleys properly, with the top of the belt sitting flush with the outside diameters of the pulleys, or just slightly above the outside diameter of the pulley, showing a "belt ride-out" as shown in the diagram above.

If the belt is sitting deeper in the pulleys, this indicates that the sides of the belt are appreciably worn and that measuring the top-width of the belt may result in an under-sized belt. Measure the top width of the pulley's v-section as a check.

Next, determine the belt's depth of section. This is found by measuring its cross-section (distance from the top-outside surface to the inside surface).
Be careful; old belts may be distorted or so badly worn on the inside surface that the measurment may not be accurate, so a check of the depth of the V-section in the pulleys may be necessary. A selection of plastic gauges for checking the size and angle of a pulley's V-section are available.
Remember that typically, a V-belt should NOT completely fill, NOR sit right at the bottom of the pulley's V-section; as doing so would reduce the grip of the drive and result in belt slippage under load.

Once the top-width and depth of the belt are found, the product-ranges for the job may be selected from our Belt-finder page.

 

GLOSSARY

 

Defining V-Belt Lengths

Specifying the length of a belt can be confusing. Although it is normally recommend using effective length; outside, inside, pitch and nominal length are frequently used; and switching between these terms can be confusing!

1. Outside Belt Length (La): The outside length of a belt is usually measured with a tape under no tension. Its validity is questionable since some belts have an arched top whereas others are flat. The use of this measure therefore, would give different readings for two otherwise identical belts. It can be used only as an approximation.

2. Inside Belt Length (Li): The inside length is measured with flat pulleys or a tape measure. As with the outside length, the inside length varies with the manufacturer. This length, ideally, should not be used.

3. Belt Pitch Length (Lp): The pitch length of a belt is the length at the pitch diameter of the sheaves being used.

Classical industrial belts are specified in terms of pitch length. The pitch length is obtained by adding the pitch circumference of one sheave to twice the centre distance between two equal diameter sheaves at a specified tension. [More recently changed to datum length.]

The belt pitch length is normally the length at the belt pitch line. This line is generally located at the neutral axis near the cord line and varies with cross section and construction. The pitch of the belt and sheave is actually a theoretical point that relates to the more accurate, reliable, and useable effective diameter and effective length.

4. Belt Effective Length (Le): The effective length of a belt is the length about the effective outside diameter of a sheave at a specified tension. The effective outside diameter of a sheave is measured where the groove top width is a dimension as specified by RMA, ASAE or SAE standards. The effective length is obtained by adding the effective outside circumference of one sheave to twice the center distance between the two standard measuring sheaves at the standard measuring tension.

5. Nominal Belt Length (Ln). The nominal length is used to refer to the length and cross section of a specific belt, and can reflect the Outside Belt Length (La), the Inside Belt Length (Li) or the Belt Pitch Length (Lp) and can refer to units being in inches OR millimeters !
For example, an A38 has a nominal length of 38 inches, referring to its Li; but an SPA1280 has a nominal length of 1280mm, referring to its Lp. The nominal length is best considered as being for designation purposes.

With all the terms used, it is easy to see how identifying the proper belt-length can become confused!.

Sheave: A sheave is a wheel or roller with a groove along its edge for holding a belt, rope, or cable. The words sheave and pulley are sometimes used interchangeably. Multiple Rollers/Sheaves can be mounted on shafts and connected by belts to efficiently transfer rotational power from a power-source to a final-drivedestination or multiple final-drive destinations.

Vari-speed or Variable Speed arrangements: A sheave can also refer to a pulley which has an adjustable operating diameter for use with a mechanical belt (sometimes called a vari-speed belt). This is accomplished by constructing the pulley out of several pieces. The two main "halves" of the pulley (the angled faces) can be moved closer together or farther apart - this allows the v-belt (a wider-than-normal variable speed belt) to move higher or lower in the groove, thus altering the operational diameter, and the gearing & speed achieved. The usual construction is some sort of locking collar or set screws to secure the components, one half with a threaded central shaft and one half with a threaded center. By rotating the components one can "screw" the parts closer together or further apart, thus changing the distance between the two halves and allowing the belt to ride higher or lower in the grove. The adjustments are constrained to a specific range of size and are not limitless.

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