DescriptionSelecting dual v-belt pulleys

 

V-belt pulleys (also called vee belt sheaves) are devices which transmit power between axles by the use of a v-belt, a mechanical linkage with a trapezoidal cross-section. Together these devices offer a high-speed power transmission solution that is resistant to slipping and misalignment.

 

V-Belt Pulley Operation 

 

V-belt pulleys are solely used for transmitting power between two parallel axels. The most notable difference between a v-belt pulley and other types of pulleys (round belt, flat, etc.) would be the geometry of the groove or grooves located around the circumference of the pulley; these grooves guide and gain traction on a v-belt. The accompanying video offers a comprehensive overview of some v-belt basics, as well as their advantages and variations.

 

Video credit: spiritjunky via YouTube

 

A v-belt is a unique mechanical linkage with a cross-section that resembles an isosceles trapezoid. The v-belt and its complementing pulley create the most efficient belt drive known (sometimes achieving 98% transmission efficiency). V-belts were developed in the early days of automobile innovation to improve belt reliability and torque transmission from the crankshaft to rotating assemblies. V-belts remain a common type of serpentine belt today.

 

V-belt transmissions are a notable upgrade from round or flat belt transmissions; v-belts provide excellent traction, speed, and load capabilities, while enjoying an extended service life with simple replacement. Heavy loads actually increase transmission efficiency since they wedge the belt further into the pulley's groove, thereby improving friction. Typically, v-belt drives operate between 1,500 to 6,000 ft/min, with 4,500 ft/min the ideal capacity for standard belts. Some narrow v-belts can operate at speeds of up to 10,000 ft/min, but these pulleys must be dynamically stabilized. V-belt pulleys may be placed in a side-by-side configuration or a single pulley may feature multiple grooves around the circumference in order to accommodate a multiple-belt drive. This type of drive distributes torque across several belts and provides a mechanical redundancy.

 

Selecting v belt pulleys  Selecting cogged teeth belt

Images credits: Main Supplies; Switchboard

 

V-belt drive advantages V-belt drive disadvantages
Minimal maintenance w/ no lubrication Approx. temperature limit of 140° F
Extremely reliable Pulleys must be somewhat larger than in other belt drives
Gradual wear, which is easily identified Center distance between pulleys is limited (no more than 3x the diameter of the largest pulley
Wide horsepower and speed range Usually more expensive than other drives
Quiet operation Only acceptable for parallel shafts
Vibration dampening  
Prevents overload  

 

Types of V-Belt Pulleys

 

Several types of pulleys are used in v-belt transmissions, each with different implementation. Occasionally flat-belt pulleys are suitable when the backside of the v-belt is used to rotate the pulley in the opposite direction of the driven pulley, as commonly employed with ribbed v-belts.

 

  • Standard pulleys are pulleys that have traditional dimensions, with one or multiple grooves, which mate with classic, small-engine, and hexagonal-style v-belts.

Selecting standard v-belt pulleys

Image credit: Carlisle Power Transmission

 

  • Companion pulleys contain integral spokes which run radially on the pulley. This produces a high strength-to-weight ratio advantageous to fractional horsepower pulleys.

Selecting companion pulleys

Image credit: Advanced Bearing

 

  • Idler pulleys are used solely as belt tensioners in many v-belt drives, but play an important part in maintaining the tension required to drive the transmission. Idlers can interact with either the wedged or flat side of the v-belt since no torque is required to be transmitted to this axle. Idler pulleys reduce belt service life and the efficiency of the drive, but are required in transmissions where the drive needs to clear obstructions, or the driven pulley does not maintain a sufficient arc of contact with the v-belt to transmit torque.  

Idler pulley options

Image credit: Just Commodores

 

  • Variable speed pulleys have a variable pitch which adjusts the driven RPM, often within a range that is represented as a percentage. These pulleys are also useful for maintaining belt tension for dynamic loads.

Selecting variable speed pulleys

Image credit: Hi-Lo 

 

  • Step pulleys have two or more non-adjustable grooves which have different pitches located around the same shaft. These pulleys change the speed ratio of the transmission.

Selecting v-belt step pulleys

Image credit: Unisoft

 

Common materials of construction include: aluminum, brass, cast iron, plastic, stainless steel, steel, and zinc alloy. For v-belts which exceed 6,500 RPM, pulleys must be manufactured within closer tolerances to ensure stability. The following chart should be referenced.

 

Table Credit: Carlisle Transmission Products

 

V-Belt Pulley Components

 

Grooves

 

Pulleys are manufactured with grooves that are designed for a specific style and width of v-belt. A more comprehensive look at v-belts is offered in the v-belt and v-ribbed belts selection guide. Conventional and narrow v-belts are frequently cogged to improve the belt's flexibility and heat dissipation, but pulleys do not require any design alterations to interact with cogged v-belts. Cogged belts are typically represented by an 'X' in the belt denomination. Pulleys for conventional and narrow v-belts are frequently interchangeable provided the pitch widths and angles are equivalent.

 

Belt style Denomination/top width

Conventional: most common v-belt style; used  in many transmission applications

A: .5"

B: .625"

C: .875"

D: 1.25"

E: 1.5"

Fractional Horsepower: a v-belt for light loads and small engines

2L: .25"

3L: .375"

4L: .5"

5L: .65"

Narrow: as strong as conventional v-belts, but with smaller widths

3V: .375"

5V: .625"

8V: 1.0"

Hexagonal: a v-belt with a hexagonal cross-section which can gain traction on pulleys placed inside or outside the belt drive. 

AA: .5"

BB: .625"

CC: .875"

 

Mounting

 

Primarily, the bore diameter of the pulley must be a geometric match with the mating shaft. The shaft about which the pulley rotates is an axle, and the most common method of accommodating this axle is by the use of a simple bore, whereas the pulley is allowed to freely rotate about the axis with no torque transmitted. This bore is used in idler pulley applications, but is otherwise useless for power transmission. Other mounting styles include:

 

  • Set screw: A through-hole allows a screw to be perpendicularly tightened against the axle.
  • Keyway: An offset slot or shaft ensures an intimate fit along the axle to transfer torque between components.
  • Press-on: An offset slot or shaft ensures an intimate fit along the axle to transfer torque between components.
  • Weld-on: The pulley's hub is directly attached to the axle via welding.
  • Taper bushing: A bolt-on tapered hub locks around the shaft.

  • Clamped hub: A split hub is tightened around the axle by the use of a clamp.Selecting v belt drives

V-Belt Pulley Specifications

 

The following parameters are important when selecting v-belt pulleys.

  • Belt profile, or the style and sizes of the belt being integrated.
  • Outside diameter, or the distance across the pulley when measured between groove edges.
  • Center diameter is the distance or distances between the shafts of the pulleys in the transmission. V-belt transmissions are limited by center distances, which must be no more than three-times the diameter of the largest pulley, lest significant slipping can occur.
  • Grooves, the grooves located on the pulley, including the number, and angle and width of the flanges.
  • Pitch diameter, or the diameter of the pulley where the belt is engaged, and is critical to the drives strength-to-weight ratio.
  • Arc of contact, the degree of which the belt wraps around the pulley.

V-Belt Pulley Standards

 

The standards below are common industrial standards related to v-belt pulleys and their implementation into a v-drive.

 

  • BS 3970 (Specifications for belt drives and their corresponding pulleys)
  • ISO 2790 (Automotive v-belt drive standards)
  • ISO 5290 (Grooved pulleys for narrow v-belts)

  • ISO 9980 (Groove geometry for v-belt pulleys)

Resources

 

Carlisle Power Transmission Products, Inc. - Industrial V-Belt Drives Design Guide (.pdf) 

 

Baldor & Maska - V-Belt Drive Selection Handbook (.pdf) 

 

Engineer's Edge - V-Belt Application 

 

Technology Transfer Services - Belt Drive Wiki 

 

Image credits:

 

Carlisle Power TransmissionHi-Tek Balancing