Tighteners-Idlers
Browning belt and chain tighteners and idler assemblies maintain drive tension as components wear. Spring-loaded and adjustable designs mount to standard brackets.
About Tighteners-Idlers
A tightener or idler applies tension to a belt or chain drive that cannot be tensioned by moving the motor. It takes up the slack that appears as belts and chains bed in and wear, and it can be positioned to increase the arc of contact on a small sheave or sprocket so the drive carries more torque without slipping. The same hardware also damps the slack-side whip that shortens chain life on long center distances.
Also known as: drive tighteners, belt tensioners, chain tighteners, idler pulleys, idler sprockets
How to choose tighteners-idlers
- Decide whether the idler runs inside or on the back
- An idler bearing on the inside of a V-belt must be grooved to match the belt section, because it carries the belt in its grooves exactly as a sheave does. An idler running on the back of the belt must have a flat face instead. The two are not interchangeable, and fitting the wrong face is the most common cause of rapid belt failure on a retrofit.
- Keep the diameter as large as the space allows
- Every idler bends the belt or articulates the chain an extra time per revolution, and the smaller the diameter, the more severe that flex. A back-side idler bends a V-belt the opposite way to its natural curve, which is the harshest duty of all, so it should be the largest diameter the layout will accept.
- Match a chain idler to the chain, not just the shaft
- An idler sprocket has to share the pitch and the strand count of the chain it runs on. A single-strand sprocket on a double-strand chain will engage on one row only and destroy both parts, so confirm the chain size before the bore size.
- Choose spring-loaded or manually set
- A manually adjusted tightener is set once and re-checked on a maintenance interval, which suits drives that are inspected regularly. A spring-loaded or gravity tensioner tracks wear continuously and suits drives that are hard to reach, at the cost of a moving assembly that itself needs checking.
- Confirm the bearing carries the tension load
- An idler is a loaded bearing, not just a wheel: it sees roughly the vector sum of the tension in the two belt or chain spans it sits between. Check the unit's radial load rating and speed limit against the drive rather than assuming any idler of the right diameter will do.
Specifications explained
| Specification | What it means |
|---|---|
| Belt section | The V-belt cross-section the grooved face is cut for (A, B, 3V, 5V and so on). It must match the belt already on the drive. |
| Chain size | The ANSI roller chain pitch an idler sprocket is cut for, which fixes the tooth form and the chain it can engage. |
| Outside diameter | The working diameter of the idler face. Larger diameters flex the belt or chain less and extend its life. |
| Bore | The shaft or stud diameter the idler mounts on, which determines the bracket and pin it can be carried by. |
| Number of grooves | How many belts a grooved idler carries. It has to equal the number of belts in the drive it tensions. |
| Maximum speed | The rotational limit for the bearing and seal in the idler, above which lubrication and heat become the limiting factor. |
Common questions
Should a tightener go on the slack side or the tight side?
On the slack side. Tensioning the tight side works against the pull the drive is already producing and raises the load on both shafts and their bearings, while an idler on the slack side takes up the loose span and increases wrap where it does some good.
Does adding an idler shorten belt life?
It adds one more flex per revolution, so it always costs some life, and a back-side idler costs the most because it bends the belt against its natural curve. Using the largest practical diameter and keeping the idler correctly aligned limits that cost considerably.
Do I still need a tightener if the motor sits on an adjustable base?
Usually not. An adjustable motor base tensions the drive by moving the center distance, which is the preferred method because it adds no extra bending. Tighteners exist for drives where the centers are fixed, where the wrap on the small sheave is too small, or where the span is long enough to whip.
Can one idler tension a multiple-belt drive?
Yes, provided the grooved idler has at least as many grooves as the drive has belts and the belts are a matched set. A single-groove idler on a multiple-belt drive tensions one belt and leaves the rest slack, which overloads the one it is bearing on.
