KEVOS® MAKEOS · Power Transmission
Double V-Belt Drive by Allowable Tight Side Tension (AA, BB, CC, DD)
For a double V-belt (hexagonal) drive with AA, BB, CC or DD belts, what tight side tension can one belt carry on each sheave, what effective pull and tight side tension does my design power produce, and how many belts does the drive need?
Double V-belt drive by the ANSI/RMA IP-21 tension method the handbook gives, for a drive of two sheaves: belt speed S = r d ÷ 3.820 (thousands of ft/min), effective pull Te = 33 Pd ÷ S (lbf, Pd in hp), tight side tension TT = Te × R ÷ (R − 1) with the tension ratio factor read for the arc of contact, slack side tension TS = TT − Te, the allowable tight side tension per belt by the formulas Tr = K1 − K2 ÷ d − K3 S² − K4 log S for each cross section on each sheave, and the number of belts Nb = TT ÷ (Tr Kf) with the length-flex correction factor Kf.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Cross section | choice | Double V-belt cross section. |
| Effective diameter of the small sheave | mm | Effective diameter of the smaller sheave. |
| Effective diameter of the large sheave | mm | Effective diameter of the larger sheave. |
| Centre distance C | mm | Distance between the shaft centres. |
| Speed of the faster shaft | rpm | Speed of the faster (smaller sheave) shaft. |
| Factors from the handbook tables | ||
| Tension ratio factor R ÷ (R − 1) for the arc (Table 21) | Tension ratio factor R ÷ (R − 1) read from the handbook table for the arc of contact shown. | |
| Length-flex correction factor Kf (Table 20) | Length-flex correction factor read from the handbook table for the effective length ÷ number of sheaves. | |
| Duty | ||
| Power to transmit | kW | Power the drive must transmit. |
| Service factor | Service factor for the driver and driven machine. | |
| Belts you will fit | belts | Number of belts you will fit. |
What each input means
Open an input to see what it is, its units, the worked example and the common mistakes, with a small diagram.
What this means: Cross section
- What it is
- Cross section of the double V-belt to rate.
- Units and format
- Choose one of 4 options from the list: AA; BB; CC; DD.
- Example
- The form opens with “BB” selected as a worked example. Choose the option that matches your case.
- Effect on the result
- Sets the constants of the rating formula.
- Get it right
- Use the handbook selection chart for the design power and speed of the faster shaft.
What this means: Effective diameter of the small sheave
- What it is
- Effective diameter of the smaller sheave of the drive.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 5000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 160 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A larger sheave allows more tight side tension per belt.
- Get it right
- Effective diameter = nomenclature diameter + 2hd − 2ap from the handbook table.
What this means: Effective diameter of the large sheave
- What it is
- Effective diameter of the larger sheave of the drive.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 10000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 315 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Sets the arc of contact and the tension allowed on that sheave.
- Get it right
- Found the same way as the small sheave’s effective diameter.
What this means: Centre distance C
- What it is
- Distance between the centres of the two shafts.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 100000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 900 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A shorter centre distance reduces the arc of contact.
- Get it right
- Measure between shaft centres with the belt at working tension.
What this means: Speed of the faster shaft
- What it is
- Speed of the faster shaft, the one with the smaller sheave.
- Units and format
- Enter a number in rpm: revolutions per minute. The form accepts 0.000001 rpm to 100000 rpm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1450 rpm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The rating rises with speed until the belt speed limits it.
- Get it right
- Use the motor speed for a speed-reducing drive.
Factors from the handbook tables
What this means: Tension ratio factor R ÷ (R − 1) for the arc (T…
- What it is
- Tension ratio factor R ÷ (R − 1) for the arc of contact on the driver.
- Units and format
- Enter a plain number with no unit. The form accepts 1 to 5. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1.22 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Raises the tight side tension for small arcs.
- Get it right
- Read it from the handbook table for the arc of contact shown.
What this means: Length-flex correction factor Kf (Table 20)
- What it is
- Length-flex correction factor for the belt.
- Units and format
- Enter a plain number with no unit. The form accepts 0.000001 to 2. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.95 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Multiplies the allowable tight side tension per belt.
- Get it right
- Read it from the handbook table for the effective length ÷ number of sheaves.
Duty
What this means: Power to transmit
- What it is
- Power the drive must transmit to the driven machine.
- Units and format
- Enter a number in kW: kilowatts. The form accepts 0.000001 kW to 100000 kW. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 11 kW as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Times the service factor, sets the design power.
- Get it right
- Use the motor rating or the measured power of the driven machine.
What this means: Service factor
- What it is
- Factor for the type of driver, driven machine and hours of running.
- Units and format
- Enter a plain number with no unit. The form accepts 1 to 5. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1.3 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Raises the design power the belts must carry.
- Get it right
- Take it from the handbook service factor tables for the belt type.
What this means: Belts you will fit
- What it is
- Number of belts you intend to fit on the sheaves.
- Units and format
- Enter a number in belts: belts. The form accepts 1 belts to 100 belts. Use a whole number. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 6 belts as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Fails the drive when fewer belts are fitted than needed.
- Get it right
- Fit at least the number the tool shows as needed.
Method and formulas
- d in inches, r = rpm ÷ 1000; S = r d ÷ 3.820; Pd = power × service factor in hp; Te = 33 Pd ÷ S lbf.
- TT = Te × R ÷ (R − 1); TS = TT − Te.
- Tr = 118.5 − 318.2 ÷ d − 0.8380 S² − 25.76 log₁₀ S (AA); 186.3 − 665.1 ÷ d − 1.269 S² − 39.02 log S (BB); 363.9 − 2060 ÷ d − 2.400 S² − 73.77 log S (CC); 783.1 − 7790 ÷ d − 5.078 S² − 156.1 log S (DD).
- Nb = TT ÷ (Tr Kf) on each sheave; the larger, rounded up, governs.
- Example: the tight side tension is 1,436.3 N and one belt allows 261.06 N on the small sheave, so the drive needs 6 belts.
Limitations
- This tool covers a drive of two sheaves; serpentine drives with several loaded sheaves follow the handbook’s fourteen steps around the drive.
- The tension formulas are not corrected for tension ratio or length-flex; the tool applies Kf as the handbook directs.
- The effective belt length is best found from a scaled layout, as the handbook advises.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Find the number of double V-belts for a drive
- Check the tight side tension against the belt allowable on each sheave
- Work out effective pull and slack side tension
Who it is for
- Machine designers
- Maintenance engineers
- Drive and conveyor designers
What you get
- Belt speed and arc of contact
- Effective pull, tight and slack side tensions
- Allowable tight side tension per belt on each sheave
- Number of belts needed
Interpreting the result
- Slip usually occurs first at the driver, which the tension ratio factor allows for.
- The smaller sheave allows less tension, so it usually decides the number of belts.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 2505–2510. Topic reference; no source tables or recommended settings are reproduced.
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Open the Double V-Belt Drive by Allowable Tight Side Tension (AA, BB, CC, DD) calculator