Bucket Elevator Capacity, Speed, and Power

A bucket elevator does not fill its buckets: at the boot the buckets scoop or are fed, and how much they pick up depends on the material's flowability, the boot design, and the speed. Seventy-five percent is a working figure for free-flowing grain and considerably less for a sluggish material, and rating an elevator at 100% fill is how a system bought for 20 tons an hour delivers 15. The fill factor's leverage is worth seeing directly: the same machine at 60% fill rather than 75% delivers 16.2 tons per hour instead of 20.3, and no amount of extra motor recovers it -- the fix is at the boot, not at the drive. Power is dominated by LIFT, which is the opposite of a horizontal conveyor. Friction, scoop resistance, and drive losses are the smaller corrections, so elevator power scales almost linearly with height and with tonnage and is quite insensitive to everything else. Buckets of 0.05 cubic ft on 8 in centers at 250 fpm and 75% fill move 844 cubic ft an hour, which is 20.3 tons of 48 lb grain, and lifting it 60 ft takes 1.23 horsepower before losses and about 2 hp at the motor. Two horsepower to lift twenty tons an hour sixty feet is why bucket elevators are the cheapest vertical conveying there is. Capacity and power only. This does not select buckets, belt, or chain, does not size the head and boot pulleys or the shaft and bearings, does not check belt tension or the take-up, and does not address the discharge -- centrifugal, continuous, or positive -- which sets the speed a given bucket can actually run at. Legs handling grain and other combustible dusts are governed by NFPA 61 and NFPA 68 for explosion venting, and none of that is addressed here. The elevator manufacturer, the material's own test data, and NFPA govern.

buckets per foot = 12 / spacing_in; capacity = bucket volume x buckets per foot x speed x 60 x fill factor; mass rate = capacity x bulk density; lifting hp = (mass rate / 60) x lift / 33,000; motor hp = lifting hp / drive efficiency x scoop allowance.

Bucket elevator volumetric capacity and lifting horsepower by their standard relations, by name; the fill factor and the scoop-and-friction allowance are entered rather than assumed, and 1.2445 cubic ft per bushel is the US bushel. Capacity and power only, and NO position on combustible grain dust, which NFPA 61 and NFPA 68 govern. The elevator manufacturer and the material's own test data govern.

Volumetric arithmetic on the user's own bucket, spacing, speed, and material figures; no manufacturer capacity table is reproduced.

Estimate. AHJ and licensed professional govern.

Field names used by the API: bucket_volume_ft3, spacing_in, speed_fpm, fill_factor, bulk_density_pcf, lift_ft, drive_efficiency, friction_allowance, buckets_per_ft, capacity_ft3_hr, mass_lb_hr, tons_per_hr, bushels_per_hr, lifting_hp, motor_hp

• Buckets are never full fill factor is the honest term and it is a material and boot property, not a machine ratingbucket elevator practice
• Lift dominates power friction and scoop resistance are corrections; power scales with height and tonnagebucket elevator practice
• No dust-hazard position grain and other combustible dusts are governed by NFPA 61 and NFPA 68NFPA 61 / NFPA 68