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Free pulley tester `could save thousands`
Published:  01 November, 2006

Free pulley tester `could save thousands`

Fenner has produced a simple device for checking the wear on pulley grooves. It claims that the device, which it is giving away, could improve pulley efficiencies by 10%, saving users thousands of pounds a year.

Although most users of V and wedge belt drives know that they should replace their belts about once every three years, they often assume that the cast-iron pulleys do not wear. However, pulleys do wear and this can lead to wasted energy and the need to replace belts more frequently. Although pulleys wear more slowly than belts, once a pulley groove is out of shape, it can result in belt slippage which, in turn, accelerates wear in both components.

The most noticeable effect of pulley groove wear is rapid deterioration of the belt. Before this happens, however, the belt drive efficiency will already have dropped because belt slippage results in speed loss, and inefficient operation.

For example, a 37kW electric motor running continuously on an average tariff of 6p/kWh, will cost £17,250 per year to run. Worn pulley grooves can easily waste 10% of the input energy — equivalent to £1,725 per annum. With losses on this scale, replacement pulleys can pay for themselves in less than two months.

Fenner`s free pulley groove gauge (above) consists of eight size measures held on a key ring. The best fit depends on the bend radius of the belt, so larger pulleys — those over 190mm diameter for a SPB groove section — require a groove angle of 38 degrees. For smaller pulleys, the figure is 34 degrees. Each key ring has two star-shaped gauges — one for larger pulleys, and one for smaller pulleys.

To use the gauge, a section of the pulley is cleaned and the appropriate profile is fitted into the groove. The pulley needs to be replaced if there is 5% or more wear at its pitch-line — the point one third of the way down from the top of the pulley where the stiffer load-bearing section of the belt rests.

A good rule-of-thumb is that the point of the gauge should be clear of the bottom of the pulley groove, with no daylight being visible on either side of the gauge (as shown on the left, above). Pulley grooves tend to wear to a round profile and this allows light to pass on either side of the straight-edged trapezoid shape of the gauge (as shown on the right).

When a pulley`s groove flanks are worn, the belt sits further down in the pulley and thus becomes slacker, resulting in slippage. Belt drives can usually be adjusted to reduce slack, but there are two limiting factors. When a belt becomes slack and starts to wear, its profile changes and it becomes inefficient. As the pulley grooves change from flat- to round-sided, and the belt reaches the bottom of the groove, there is no wedging mechanism and the belts will start to slip and wear quickly. Using cogged belts can help, but eventually the pulley will need to be replaced.

Belts may have to be removed to check the pulley grooves, but it is generally possible to get a good measure by simply removing all or part of the drive guard.

If you wish to obtain a free Fenner pulley groove gauge, please send a request to

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