Required line pull
Required line pull
Required Line Pull = W × (GR + CF)
- W
- weight of the load (lbs)
- GR
- grade resistance (table below)
- CF
- coefficient of friction (table below)
Coefficients of friction
Approximate ranges.
| Surfaces | Coefficient of friction (CF) |
|---|---|
| Steel on steel | 0.40 – 0.60 |
| Wood on concrete | 0.40 – 0.60 |
| Steel on concrete | 0.30 – 0.70 |
| Load on wheels | 0.02 – 0.05 |
| Load on rollers | 0.05 – 0.10 |
Grade resistance
Percent grade
% Grade = AB
- A
- rise
- B
- run
| % Grade | Grade resistance (GR) |
|---|---|
| 5 | 0.050 |
| 10 | 0.100 |
| 20 | 0.196 |
| 30 | 0.288 |
| 40 | 0.372 |
| 50 | 0.448 |
| 60 | 0.513 |
| 70 | 0.573 |
| 80 | 0.624 |
| 90 | 0.669 |
| 100 | 0.701 |
| 200 | 0.896 |
| 400 | 0.970 |
| Vertical | 1.000 |
Using multiple parts of line
When the required line pull is more than the unit’s single line pull, reeve the rope through sheaves.
- Divide the total required line pull by the available single line pull. The result is the multiplier.
- In the column for your sheave type, find the first value greater than the multiplier. The number of parts of line is in that row.
| Parts of line | Nylatron sheaves | Bronze bushed sheaves | Roller bearing sheaves |
|---|---|---|---|
| 2 | 1.86 | 1.91 | 1.96 |
| 3 | 2.58 | 2.76 | 2.88 |
| 4 | 3.16 | 3.53 | 3.77 |
| 5 | 3.60 | 4.24 | 4.63 |
| 6 | 3.90 | 4.89 | 5.45 |
| 7 | — | 5.48 | 6.24 |
| 8 | — | 6.03 | 7.00 |
Worked example
Total required line pull is 7,400 lbs; available single line pull is 2,000 lbs.
7,400 lbs ÷ 2,000 lbs = 3.70 multiplier
- Nylatron sheaves: the first value above 3.70 is 3.90 → 6 parts of line
- Bronze bushed sheaves: the first value above 3.70 is 4.24 → 5 parts of line
- Roller bearing sheaves: the first value above 3.70 is 3.77 → 4 parts of line
Rig 6 parts with Nylatron sheaves, 5 with bronze bushed sheaves, or 4 with roller bearing sheaves.
More on reeving, including diagrams: Utilizing Multiple Parts of Line.