Belt Power from Tension and Speed

The power a belt actually transmits, from the two tensions and the belt speed.

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Example

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Checked against published worked examples from: McGraw-Hill (Budynas and Nisbett).

Details, formula, and sources

ScopeP = (T1 - T2) V / 33000 hp, with V = pi D N / 12 ft/min. The point people miss: only the DIFFERENCE of the tight- and slack-side tensions (the effective tension Te = T1 - T2) does work -- the average tension just clamps the belt for grip and transmits nothing. A 250-to-100 lb drive on a 6 in sheave at 1,750 rpm runs 2,749 ft/min and passes 12.5 HP; a tighter 400-to-250 lb drive keeps the same Te of 150 and the same 12.5 HP while carrying far more total tension into the bearings. Over-tensioning buys wear, not capacity. A design aid; the belt/sheave ratings and wrap angle govern.

Formula or tableV = pi D N / 12 (ft/min); Te = T1 - T2; P = Te V / 33000 (hp).

Source and editionThe belt power relation P = (T1 - T2) V / 33000, first-principles as in Machinery's Handbook / the Gates Industrial Drive Design Manual, by name.

Free accessThe power-from-effective-tension relation is a standard first-principles result; the tensions and speed come from the drive. Free at gates.com/literature.

What governsEstimate. AHJ and licensed mechanical contractor govern. ACCA Manual J / D / S supersede rules of thumb.

API field namestight_side_tension_lb, slack_side_tension_lb, sheave_diameter_in, sheave_rpm, power_hp, belt_speed_fpm, effective_tension_lb

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