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How to Determine Belt Needs
Click here for power ratings for PowerTwist Plus, NuTLink and SuperTLink belting
Service Factors (Table 1)
Arc of Contact Correction Factor (K) for V-Belt Drives (Table 2)
Belt Length Correction Factors (LC) (Table 3)
This page offers some information on how to determine the belt type for a particular drive. Before you can proceed, you need to know the following four things:
1. The type of application or driven machine. 2. The type of prime mover, its HP rating and RPM. 3. The speed of the driven machine or speed ratio. 4. The approximate center distance between shafts. |
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Step 1. Find the Design Horsepower
- From Table 1 we select 1.2 SF, i.e. NEMA A motor, Fan up to 10 HP
- DHP = 7.5 HP x 1.2 SF = 9.0 DHP
Step 2. Review the Drive
- Calculate the speed ratio. This is large diameter divided by small diameter.
6.8 ÷ 5.4 = 1.26:1
- Calculate Belt HP Rating
- Refer to the PowerTwist Plus power rating table for “B” cross section belt. Using the faster shaft RPM of 1750, read across to column headed 5.4" and find 5.43. This is the basic HP rating. Read across on the same line under the Add-on Horsepower rating section, in column headed 1.21 to 1.27, read .19. Adding .19 to 5.43 gives 5.62 rated HP per belt.
- Determine the Arc of Contact Correction Factor
- Calculate (D - d) ÷ C and find factor KØ from Table 2.
Where: D = 6.8, d = 5.4 and C = 22 (6.8 - 5.4) ÷ 22 = 0.06
Factor KØ is 1.00.
- Determine Belt Length and Length Correction Factor (LC) 1. Using the formula below calculate the belt length and from Table 3 find the Length Correction Factor (LC).
Where: D = 6.8, d = 5.4 and C = 22
Belt Length = 63.2 inches
From Table 3, under “B” cross section and between a 60 and 68 inch
belt factor LC is .93.
![Belt Length = 2C + 1.57 (D+d) + [(D-d)2/4C]](../assets/belt_calc.gif){kind=small}
- Calculate Corrected HP per Belt
1. Corrected HP per Belt = Rated HP per belt x Factor KØ x Factor LC
Corrected HP per Belt = 5.62 x 1.00 x .93 = 5.23
Step 3. Find the Number of Belts Required
- Divide the Design Horsepower by the Corrected Horsepower per belt to find the number of belts required. The answer will usually contain a fraction; therefore always round up to the next whole number of belts. DHP ÷ CHP = 9.0 ÷ 5.23 = 1.72.
Two PowerTwist Plus belts are okay for the application.
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