V-Belt Pulleys

What are V-belt pulleys?

V-belt pulleys, also called sheaves, are grooved wheels that transmit power from one shaft to another using V-belts. Each pulley has one or more V-shaped grooves around its rim. When the belt is tensioned, its tapered sides wedge into the groove, creating a strong grip that drives the belt without slipping. By using pulleys of different diameters, a belt drive can also increase or reduce speed between a motor and the machine it drives.

A standard V-belt pulley is made up of:

• A rim with one or more V-shaped grooves, machined to suit a specific belt section
• A web, or spokes on larger sizes, connecting the rim to the hub
• A hub with a bore, which mounts the pulley onto the shaft
• A fixing method, such as a taper bush or a keyway and set screw.

The groove profile is the most important feature.

• Each groove is machined to a set width and angle to suit one belt section, so the belt sits at the correct height and grips both sides of the groove.
• Using the wrong belt in a groove causes slipping, overheating, and rapid wear of both the belt and the pulley.

V-belt pulleys are described by their belt section, pitch diameter, number of grooves, and bore type.

Why are V-belt pulleys essential?

V-belt pulleys are found in almost every type of industrial drive. They give a simple, quiet, and economical way to transmit power, change speed, and drive several machines from one motor. The belt also absorbs shock loads and vibration, protecting motors and gearboxes from damage.

Because the belts can slip slightly under extreme overload, V-belt drives also act as a safety buffer. They are easy to install and maintain, and worn belts and pulleys can be replaced quickly with standard parts.

Typical applications include:

• Electric motor drives
• Fans, blowers, and air handling units
• Pumps and compressors
• Agricultural machinery
• Conveyors and material handling equipment
• Woodworking and machine tools
• Crushers, mixers, and processing machinery
• HVAC and refrigeration equipment

The main types of V-belt pulleys

• Taper bush pulleys - Pulleys with a tapered bore that takes a separate taper bush. The bush is bored to suit the shaft, so one pulley can fit a range of shaft sizes, and it clamps tightly to the shaft without needing machining.
• Pilot bore pulleys - Pulleys supplied with a small, rough bore, which is machined out by the customer to suit the shaft, usually with a keyway and set screw added.
• Single and multi-groove pulleys - Pulleys with one groove for light drives, or several grooves to run matched sets of belts for higher power.
• Wedge section pulleys - Pulleys with grooves for SPZ, SPA, SPB, and SPC wedge belts, the most common sections in modern industrial drives.
• Classical section pulleys - Pulleys with grooves for Z, A, B, and C classical V-belts, often found on older machinery.
• Cast iron and steel pulleys - Most V-belt pulleys are cast iron, which is strong, stable, and damps vibration. Small pulleys may be made from steel.

How to choose the right V-belt pulleys?

• Belt section - Choose a pulley with grooves to match the belt section exactly, such as SPZ, SPA, SPB, or SPC.
• Pitch diameter - Choose diameters to give the speed ratio needed, and never go below the minimum recommended pulley size for the belt section, as small pulleys bend the belt sharply and shorten its life.
• Number of grooves - Choose enough grooves to carry the power of the drive, with one belt per groove.
• Bore type - Choose a taper bush pulley for quick fitting and easy removal, or a pilot bore pulley where the bore will be machined to suit.
• Taper bush size - Check the taper bush size suits the pulley and that the bush is available in your shaft size.
• Speed - Check the rim speed of the pulley is within the maximum allowed for its material and size.

Essential references and specialised ranges

How the numbering works:

V-belt pulleys are usually referenced by the belt section, the pitch diameter in millimetres, the number of grooves, and the taper bush size. For example:

SPZ63-1-1108 = SPZ section, 63mm pitch diameter, 1 groove, takes a 1108 taper bush

SPA224-3-2517 = SPA section, 224mm pitch diameter, 3 grooves, takes a 2517 taper bush

SPB250-4-3020 = SPB section, 250mm pitch diameter, 4 grooves, takes a 3020 taper bush

Taper bush sizes are given in tenths of an inch:

1108 = bush around 1.1 inches across and 0.8 inches long

2517 = bush around 2.5 inches across and 1.7 inches long

Suffixes:

TB = taper bore, for a taper bush

PB = pilot bore, ready for machining

Suffix codes vary between manufacturers, so check the supplier’s catalogue for the exact meaning.

FAQ - All you need to know about V-belt pulleys

What is the difference between wedge and classical pulleys?

Wedge pulleys have grooves for SPZ, SPA, SPB, and SPC belts, which are narrower and deeper and carry more power for their size. Classical pulleys have grooves for Z, A, B, and C belts, and are common on older machinery.

Can I use a classical V-belt on a wedge pulley?

In many cases, yes. Classical belts can often run in the matching wedge groove, such as an A belt in an SPA groove. Wedge belts should not be used in classical grooves, as they will not sit correctly.

What is the pitch diameter?

The pitch diameter is the diameter at which the belt effectively runs in the groove. It is smaller than the outside diameter of the pulley and is used to work out speed ratios and belt lengths.

How do I fit a taper bush pulley?

Clean the bore and bush, fit the bush into the pulley, slide the assembly onto the shaft, and tighten the screws evenly in turn to the recommended torque. Line up the pulleys with a straight edge before fitting the belts.

How do I check pulley alignment?

Place a straight edge or laser alignment tool across the faces of both pulleys. The pulleys should be parallel and in line. Poor alignment wears belts and grooves quickly and causes noise.

How do I identify the pulley I need?

Check the code on the pulley or in the machine’s parts list. If it cannot be read, use a groove gauge to find the belt section, measure the outside diameter, count the grooves, and note the bore type and size.

How can I tell if a V-belt pulley needs replacing?

Warning signs include:

• Shiny or polished groove sides
• Belts sitting low in the groove or touching the bottom
• A dished or worn groove profile when checked with a groove gauge
• Chips, cracks, or damage to the rim
• Belts wearing quickly, slipping, or squealing
• Vibration or wobble from a damaged pulley or loose bush