Installing belts and pulleys Correctly


Although comparatively old in principle, today's belt drive is an extremely efficient method of transferring power between prime mover and machinery. Ongoing refinements of materials and processes have meant ever higher performance standards.

The best performance, lifespan and the maximum benefit from these advances can only be obtained if the belts are correctly installed. Following a few standard installation steps will ensure optimum performance is combined with a long and trouble-free life.

Before assembling the drive, check the pulley grooves are free from scores or sharp edges, and all dimensions conform to the relevant standard.

The taper lock bush is your starting point when it comes to assembly and installation. Drive installation is a straight forward job with the taper lock.

Good alignment of pulleys prior to belt installation is important to avoid belt flank wear. Common alignment faults include shafts not being parallel (Figure 1 b), shafts not being in correct alignment although they appear parallel when seen from above, and shafts being in parallel alignment whilst the pulleys themselves are not (Figure 1 c). In short, both shafts and pulleys must be parallel in alignment (Figure 1 a).

a) Correct, Installation b) Shafts not parallel c) Pulleys not parallel

Figure 1: The correct belt and pulley alignment (a) shown alongside two incorrect belt and pulley alignments. (.b :and .c ): The. dotted lines emphasise. the faults by, indicating the correct position.

When the pulleys have been correctly positioned on the shafts, the belts can be installed to complete the drive. The drive centre distance should be reduced prior to installation of the belts so that they may be fitted without the use of force. Under no circumstances must belts be prized into the grooves. Belts and pulley grooves can easily be damaged by using sharp tools to stretch the belts over the pulley rim. In addition, correct guidelines should be followed for installation allowance and take-up allowance.

Where guards are necessary it is desirable to use the mesh type to permit adequate ventilation.

If tensioning pulleys are to be used on wedge-belt drives, they must be fitted with a grooved pulley bearing on the inside of the drive, preferably on the slack side. The pulley should be positioned as close as possible to the large pulley. Flat tensioning pulleys, bearing on the outside of the drive are permissible only with 'V' type belts. They should be positioned within one third of the centre distance from the small pulley.

The tensioning pulley must be at least the same diameter as the small pulley of the drive.

Tensioning pulley movement can only be determined by laying out the drive to scale. It must allow for passing the belts over the outside diameter of one of the pulleys on installation, and should also allow for belt to stretch.




This article came courtesy of Fenner's 'Drive Design & Maintenance' manual.