Although not as important as the drive pulley, the tail pulley and snub/bend pulleys play a vital role in the proper running of a belt conveyor. The tail pulley is where the belt turns back at the loading end and, on most conveyors, it is connected to the take-up. Snub pulleys increase the wrap angle on the drive pulley or change the direction of the belt. Material building up on these pulleys is one of the most common causes of belt mistracking.
In this guide we cover the function of tail and snub pulleys, the problem of material build-up, wing pulleys, maintenance and replacement steps and spare part selection. For the drive pulley, see our conveyor pulley guide, and for general maintenance, our belt conveyor guide.
Functions
- Tail pulley: Returns the belt; on a screw take-up, this is usually the pulley that sets the tension.
- Snub pulley: Improves traction by increasing the wrap angle on the drive pulley.
- Bend pulleys: Guide the belt in gravity take-up systems and at changes of direction.
Material Build-Up and Its Link with Mistracking
A belt moves towards the larger-diameter (higher) side of a pulley. Material stuck to the return belt is carried to the tail and snub pulleys; it builds up in one area of the pulley, increasing its diameter and pushing the belt to that side. In addition, rocks getting between the return belt and the pulley damage both the belt and the pulley. Solutions:
- Effective primary and secondary scrapers (see belt scrapers),
- A V-plough scraper on the return belt in front of the tail pulley,
- A wing tail pulley for sticky material: lets material fall out between the wings,
- Regular pulley cleaning.
Failure and Wear Signs
- Material building up on the pulley face,
- Belt mistracking (especially on the return side),
- Bearing temperature and noise,
- Wear or cracks in the pulley shell,
- Bent wings on a wing pulley.
Inspection and Maintenance
| Check | Interval | Method |
|---|---|---|
| Cleaning the pulley face | Daily | After the conveyor is stopped and locked out |
| Bearing temperature and grease | Weekly | Thermometer, greasing |
| Pulley squareness to the belt | Monthly | Measurement |
| V-plough scraper | Weekly | Blade condition |
Replacement Step by Step
- The conveyor is locked out; the take-up is slackened.
- The belt is lifted off the pulley and supported.
- The bearing bolts are removed; the pulley is taken out.
- The new pulley is positioned and aligned square and parallel to the belt.
- The belt is refitted and tensioned, and tracking is adjusted.
Common Mistakes
- Trying to correct mistracking with idler adjustments while ignoring pulley build-up,
- Cleaning a pulley on a running conveyor (serious accident risk),
- Not adjusting both sides of a screw take-up equally,
- Using a wing pulley in the wrong place on a high-tension conveyor.
Troubleshooting Table
| Symptom | Possible cause | Solution |
|---|---|---|
| Mistracking on the return side | Build-up on the tail pulley, uneven take-up | Cleaning, scraper, take-up adjustment |
| Cuts in the belt | Rocks getting between pulley and belt | V-plough scraper |
| Bearing failure | Contamination, lack of grease | Check seals and grease |
An Example from the Field
On a conveyor carrying clayey material, the return belt was constantly running off. Clay several centimetres thick had built up on one side of the tail pulley. The plant switched to a wing tail pulley and fitted a V-plough scraper on the return belt; the mistracking problem disappeared.
Pre-Purchase Checklist
- Have the pulley diameter, face width, shaft and bearing dimensions been determined?
- Is a plain or wing pulley required?
- Is lagging needed?
Frequently Asked Questions
Can a wing pulley be used on any conveyor?
It is useful with sticky material; however, because of noise and its effect on the belt, the application conditions should be assessed.
Should the tail pulley be lagged?
Usually not; lagging can be useful with abrasive or sticky material.
Design Details of Tail and Snub Pulleys
Although tail and snub pulleys do not transmit torque like the drive pulley, they carry a significant share of belt tension. In gravity take-up systems in particular, the take-up pulley and bend pulleys are under high bending loads because they carry the combined tension of both strands of the belt. The following details are therefore important when choosing a pulley:
- Pulley diameter: The minimum diameter for the number of plies and type of belt carcass must be respected. A diameter smaller than required causes early fatigue of belt splices and the carcass.
- Crown profile: Slightly crowned pulleys can help keep the belt centred; however, crowning is limited on steel cord and wide belts.
- Shaft and hub connection: Hubs with tapered clamping rings have fewer loosening problems than keyed connections and are easier to dismantle.
- Shell wall thickness and end discs: Fatigue cracks usually start at the end disc–shell weld; the design must be based on a stress calculation.
- Bearing selection: In dusty environments, greasable bearing housings with labyrinth seals should be preferred.
Wing Pulley or Lagged Pulley?
| Option | Advantage | Disadvantage | Suitable for |
|---|---|---|---|
| Plain steel pulley | Simple, economical | Build-up with sticky material | Dry, clean material |
| Rubber-lagged pulley | Reduces build-up and wear | Lagging needs renewing | Slightly sticky and abrasive material |
| Wing pulley | Material falls out between the wings | Belt vibration, noise | Very sticky material, tail end |
| Spiral wing pulley | Reduces the vibration of a wing pulley | More expensive | Sticky material, more sensitive belts |
Effect of Operating Conditions on Pulley Life
| Condition | Effect | Recommendation |
|---|---|---|
| Inadequate belt cleaning | Material build-up, mistracking, wear | Primary/secondary scrapers and V-plough |
| Excessive belt tension | Bearing and shaft fatigue | Set tension correctly |
| Humid and dusty environment | Bearing failures, corrosion | Good sealing, regular greasing |
| Pulley not square to the belt | Constant mistracking, edge wear | Alignment at installation and maintenance |
Maintenance Record Form
| Field | Record |
|---|---|
| Conveyor and pulley position | Tail, snub, take-up pulley |
| Bearing temperature | Weekly measurements |
| Greasing | Date and quantity |
| Build-up condition | Cleaning need, scraper condition |
| Alignment | Measured deviation and correction made |
OEM or Aftermarket?
Tail and snub pulleys are often produced in standard sizes, so aftermarket pulleys sourced from a reliable manufacturer can be used without problems. Points to watch: pulley diameter and face width, shaft diameter and shaft end dimensions, bearing centres, shell wall thickness and weld quality, lagging type and thickness, and balance. Before replacement, all dimensions of the old pulley should be taken and compared with the pulley assembly drawing.
Stock and Supply Planning
- Keeping a spare tail pulley and bearing set for long, critical conveyors greatly shortens downtime.
- Standardising pulley and bearing dimensions across the plant lets one spare protect several conveyors.
- For lagged pulleys, a spare pulley cycle can be planned taking relagging time into account.
Post-Installation Checklist
- Is the pulley square and parallel to the belt?
- Are the bearing bolts torqued and locked?
- Has greasing been done?
- Is belt tension correct, and is there any mistracking?
- Were bearing temperature and bolts checked after the first 8 hours?
More Questions
Are the tail pulley and the take-up pulley the same thing?
On conveyors with a screw take-up, the tail pulley is also the take-up pulley. On conveyors with a gravity take-up, the take-up pulley is usually in a separate location together with the counterweight.
When is a snub pulley needed?
It is used when more wrap angle is needed on the drive pulley or when the direction of the belt is to be changed. As the wrap angle increases, the drive pulley’s traction improves.
How is material build-up on pulleys prevented?
Effective belt cleaning systems, V-plough scrapers, suitable lagging and wing pulleys for sticky material largely prevent build-up.
Spare Parts and Service for Tail and Snub Pulleys
CSP Mühendislik supplies tail, snub and wing pulleys for belt conveyors as part of its belt conveyor spare parts range, and provides service support for pulley replacement and solving mistracking problems. You can share your dimensions on WhatsApp.
