If you could fix only one thing on your V-belt drives, fix tension. A loose belt slips, squeals, glazes and burns. A tight belt overloads motor and shaft bearings and stretches itself. Both cost money, and both are avoided with a five-minute check.
Use the deflection method: push the belt at the middle of its span with a tension gauge and check that it moves about 16 mm for every 1,000 mm of span (1.6 mm per 100 mm), at the force given by the belt maker for your section and pulley size. Re-check new belts after the first few hours of running, because they settle in and lose tension.
Pressing a belt with a thumb and judging "about right" depends on the person, the belt section and the span length. A long span always feels slack; a short, heavy C-section belt always feels tight. Use a measured deflection and force instead.
| Span length | Target deflection |
|---|---|
| 400 mm | about 6.4 mm |
| 600 mm | about 9.6 mm |
| 800 mm | about 12.8 mm |
| 1,000 mm | about 16 mm |
| 1,500 mm | about 24 mm |
New belts seat into the pulley grooves and stretch slightly in their first hours. Tension drops noticeably during this run-in. Set new belts toward the upper end of the recommended range, run the drive, then re-check after the first few hours or the first day and adjust again.
| Sign | Too loose | Too tight |
|---|---|---|
| Noise | Squeal at start-up or under load | Usually quiet |
| Belt condition | Glazed, shiny sides; burn marks | Stretching; cracking |
| Pulleys | Polished grooves | Normal |
| Bearings | Normal | Hot motor or shaft bearings, early bearing failure |
| Drive behaviour | Slip, speed loss, belt flapping | Higher power draw, shaft deflection |
Squealing at start-up is the classic sign of a loose belt, especially on heavy-inertia drives such as crushers and fans. For a fuller diagnosis, see why V-belts fail early.
Belt dressings and sprays may quieten a slipping belt for a few days, but they soften the rubber and attract dirt. Fix the tension, the pulleys or the alignment instead.
Sonic tension meters, which measure the belt's vibration frequency, give the most repeatable readings and are worth having in larger plants.
How much should a V-belt deflect?About 16 mm for every 1,000 mm of span (1.6 mm per 100 mm), at the force recommended by the belt maker for the section and pulley size.
How tight should a new V-belt be?Toward the upper end of the recommended range, because new belts settle in and lose tension. Re-check after the first few hours of running.
Why does my V-belt squeal at start-up?Most often the belt is too loose for the starting load. Check tension, pulley wear and alignment.
Can a V-belt be too tight?Yes. Over-tension overloads motor and shaft bearings, stretches belts and wastes energy.
Send us the belt section, number of belts, pulley sizes and motor power, and our team will help you with the right tension for your drive.