KEVOS® MAKEOS · Power Transmission
Light Duty V-Belt Power Rating (3L, 4L, 5L, Fractional Horsepower)
For a single light duty V-belt (3L, 4L or 5L) on a fractional horsepower drive, what power can it carry on my sheave at my speed, and is that enough for the load once the combined correction factor is applied?
Power rating of light duty V-belts by the ANSI/RMA IP-23 formulas the handbook gives: HP = r [K1 d^0.91 ÷ r^0.09 − K2 − K3 r² d³] with d = d0 − 2a (the effective outside diameter of the small sheave less the 2a differential) in inches and r the faster shaft speed in thousands of rpm, for 3L, 4L and 5L sections; the rating divided by the combined correction factor for the driven machine and speed ratio, compared with the power the belt must carry.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Cross section | choice | Light duty V-belt cross section. |
| Effective outside diameter of the small sheave d0 | mm | Effective outside diameter of the smaller sheave. |
| Diameter differential 2a (Table 23) | mm | Differential 2a from the handbook table for the section; subtracted from the outside diameter to give the diameter for rating. |
| Speed of the faster shaft | rpm | Speed of the faster (smaller sheave) shaft. |
| Combined correction factor (Table 24) | Combined correction factor from the handbook table for the driven machine and speed ratio; it allows for drive geometry and service. | |
| Power the belt must carry | kW | Power the belt must transmit. |
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 light duty V-belt to rate.
- Units and format
- Choose one of 3 options from the list: 3L; 4L; 5L.
- Example
- The form opens with “4L” 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 outside diameter of the small sheave…
- What it is
- Effective outside diameter of the smaller sheave.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 1000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 76.2 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 rating diameter with the 2a differential.
- Get it right
- Measure across the outside of the sheave.
What this means: Diameter differential 2a (Table 23)
- What it is
- Differential between the outside and the rating diameter of the sheave.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0 mm to 20 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1.524 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Subtracted from the outside diameter before rating.
- Get it right
- Read 2a from the handbook sheave table for the section.
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 1750 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.
What this means: Combined correction factor (Table 24)
- What it is
- Combined correction factor for drive geometry and service.
- Units and format
- Enter a plain number with no unit. The form accepts 0.5 to 3. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1.2 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The rating is divided by it.
- Get it right
- Read it from the handbook table for the driven machine and the speed ratio.
What this means: Power the belt must carry
- What it is
- Power the single belt must carry to the driven machine.
- Units and format
- Enter a number in kW: kilowatts. The form accepts 0.000001 kW to 100 kW. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.37 kW as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Fails the belt when it is larger than the corrected rating.
- Get it right
- Use the motor nameplate power for fractional horsepower motors.
Method and formulas
- d = d0 − 2a in inches; r = rpm ÷ 1000.
- HP = r [K1 d^0.91 ÷ r^0.09 − K2 − K3 r² d³]: 3L 0.2164, 0.2324, 0.0001396; 4L 0.4666, 0.7231, 0.0002286; 5L 0.7748, 1.727, 0.0003641.
- Corrected rating = HP ÷ combined correction factor (1 hp = 0.7457 kW).
- Example: one 4L belt carries 0.48162 kW after correction, against 0.37 kW to carry.
Limitations
- Light duty belts are meant for a single belt on fractional horsepower drives; use industrial belts for heavier duty.
- The 2L section is not covered by the RMA standard.
- A zero or negative rating means the sheave is too small for the section at this speed.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Check a single light duty belt on a fractional horsepower drive
- Choose between 3L, 4L and 5L sections
- Find the smallest sheave that carries a small load
Who it is for
- Machine designers
- Maintenance engineers
- Drive and conveyor designers
What you get
- Rating diameter d = d0 − 2a and belt speed
- Horsepower rating of the belt
- Rating corrected by the combined factor
- Check against the power to carry
Interpreting the result
- The combined correction factor already includes the service factor, so do not apply a separate one.
- The rating diameter is smaller than the outside diameter by the 2a differential.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 2510–2513. Topic reference; no source tables or recommended settings are reproduced.
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Open the Light Duty V-Belt Power Rating (3L, 4L, 5L, Fractional Horsepower) calculator