V-Pulleys and Belt Standards

• PAES 301:2000 establishes specifications and provides technical information for the proper application of V-belts and pulleys for drives of agricultural machinery
• PAES 304:2000, Engineering Materials – Keys and Keyways for Agricultural Machines – Specifications and Applications contains provisions which, through reference in this text, constitute provisions of this Standard

Applications of V-Belt Drives

• V-belt drives transmit motion and power to shafts with short center distances
• V-belt drives may be operated with small pulley diameters
• Multiple V-belts may be used on a multi-grooved pulley, creating a multiple-belt drive

Definitions

• V-belt: A flexible machine element used to transmit motion and power between two shafts, with a cross-section shaped roughly like a regular trapezoid.
• V-pulley: A wheel with one or more grooved rims used to transmit motion and power by means of one or more V-belts; its cross section is in the shape of an open-channel.
• V-belt drive: A power transmission device which consists of one or more V-belts mounted on two or more V-pulleys.
• Pulley diameter: The outside diameter of the pulley.
• Pulley pitch diameter: The diameter of the pulley, which coincides with the belt pitch.
• Belt pitch: The region in the belt that keeps the same length when the belt is bent perpendicularly to its base.
• Belt length: The length of the belt at the level of its pitch.
• Speed ratio: The ratio of the angular velocities of the pulleys making no allowance for slip and creep.
• Belt speed: The linear speed of the belt at the level of the pulley pitch diameter.

V-Belts

• A V-belt is constructed of cords (cotton, rayon, synthetic, or steel) and fabric impregnated with rubber.
• Dimensions of V-belts are designated as shown in Figure 1.
• Nominal dimensions of belt cross-sections for agricultural machines are shown in Table 1.

V-Belt Specifications

• Type A cross-section: 13 mm top width, 8 mm height, 186-1,457 watts power range
• Type B cross-section: 16 mm top width, 10 mm height, 746-18,642 watts power range
• Type C cross-section: 22 mm top width, 13 mm height, 11,186-74,570 watts power range
• Type D cross-section: 32 mm top width, 19 mm height, 37,285-186,425 watts power range
• Type E cross-section: 38 mm top width, 25 mm height, 74,570 watts and up power range
• Belts of a given cross-section should operate interchangeably in standard grooves of the same cross-section.
• Belts of different manufacturers should never be mixed on the same drive.
• V-belts should be marked with type of cross-section and pitch length, and manufacturer's name/trademark.
• V-belt packaging should be marked with type of cross section and pitch length, and manufacturer's name, trademark, and address.

V-Pulleys

• V-pulleys can be single-grooved or multi-grooved.
• Dimensions are designated as shown in Figure 2.
• Minimum recommended pulley diameters are indicated in Table 2.
• V-pulleys are generally made of cast iron, cast steel, or pressed steel.
• Recommended ratio, l/d should be at least 1.5.
• V-pulleys made of cast materials have good friction and wear characteristics.
• Pulleys made of pressed steel are lighter than cast pulleys, but may have lower friction and produce excessive belt wear.
• Pulleys should be marked with type of cross section and pulley diameter, and manufacturer's name/trademark.
• Pulley packaging should be marked with type of cross section and pulley diameter, and manufacturer's name, trademark and address.

Recommended Design Practices

• Larger pulley diameters result in lower bearing loads, enabling use of smaller, less expensive belt cross-sections.
• Pulley diameters should conform to the minimum recommended values as specified in Table 2.
• The approximate belt length for a two-pulley drive (Fig. 3) may be calculated using the formula: L = 2C + (π/2)(D₁ + Ds) + (D₁ - Ds)² / 4C where L is the belt length, C is the distance between centers of pulleys, D₁ is the pitch diameter of the large pulley, and Ds is the pitch diameter of the small pulley.
• If the calculation results in a non-standard length, use the next longer standard length and correct center distance.
• To determine belt length with more than two pulleys (Fig. 4), lay out pulleys to scale when a new belt is applied and first brought to driving tension.
• Belt length is the sum of the tangents and connecting arcs around the pulley diameters: Length of arc = (D x A) / 115, where D is the pulley diameter and A is the angle in degrees subtended by the arc of belt contact on the pulley. Selection of a V-belt should be based on nature of the load, type of driving unit, horsepower rating, size of pulleys, and speeds of driving and driven units.
• Figure 5 aids in proper V-belt selection, and Tables 3–7 indicate power transmitted by one belt based on velocity and pulley size.
• Service factors (Table 8) should be used to correct for loading; multiply rated horsepower by the recommended service factor to obtain horsepower capacity.
• Correction for arc of contact for small pulley is determined from Table 9: Arc of contact = 180 - 60(DL-Ds) / C, where D₁ is large pulley diameter, Ds is small pulley diameter, and C is center distance.

Additional Considerations

• Since short belts are subjected to the action of load a greater number of times, the hours of life of a short belt are less than those of a long belt.
• Use a belt-length correction factor to achieve a proper design of belt drives.
• Values are specified in Table 10
• The corrected power is obtained by multiplying the arc correction factor, belt-length correction factor, and selected belt's power rating (Tables 3-7).
• Account for speed ratio by adding and additional power.
• Multiple Belt Drives: Determine the number of belts for multiple belt drives by dividing the drive's power capacity (section 7.3.2) by the corrected power rating (section 7.6)

Idlers

• Idlers may be necessary on agricultural belt drives to provide take-up or increase the arc of contact to obtain required drive capacity.
• The idler should be located on the slack side of the drive.
• An idler should have its axis of rotation perpendicular to the plane of the belt strand on which it runs.
• The idler mounting should be strong enough to maintain its relationship at all times.
• Idlers may be grooved or flat (Figure 6), with groove dimensions as shown in Table 2.
• Grooved idlers used as inside idlers (Figure 7), should be placed close to the large pulley.
• Flat idlers are used as either inside or outside idlers.
• Minimum recommended idler diameters are specified in Table 11.
• Recommended safety measure is to enclose the drive with covers to avoid foreign materials from contact.
• Drive inspection should be performed on a periodic basis to check the belts for wear and the tightness of keys and set screws.
• Use belts with proper markings and use proper keys as specified in PAES 304:2000.
• A. 1 Provides example of V-belt drive selection
• A. 2 Provides example of Power capacity of the drive (design power)
• A. 3 Provides example of Belt selection
• A.4 Provides example of belt speed
• A.5 Provides example of speed ratio
• A.6 Provides example of power rating of the belt
• A.7 Provides example of arc of contact

Questions about V-pulleys, their dimensions, and the Philippine Agricultural Engineering Standard PAES 301:2000. It covers parameters, calculations, and standards related to V-belts and pulleys. It also includes single and multi-grooved pulleys.