Define 'pole height'

by Emily Wilson
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Dear editor,

First, I would like to say that the magazine is excellent. Second, in your article about bucket elevators (see World Grain, March 2000, page 70), could you please make clearer the definition of "pole height"? I would at least like to know the value (in meters) of that measure in the example explained in the article.

Raul Frugoli

Engineer, ACA

San Lorenzo, Santa Fe, Argentina

Editor's reply: Machutus M. (Mac) Pimblett of Bulk Material Engineering Ltd., the author of the technical profile on bucket elevators, writes:

The pole height is an analysis of the centrifugal and gravitational forces acting on the material in the bucket. When a bucket passes over the head pulley, centrifugal forces are generated and act on the material in the bucket.

If a force diagram is constructed in magnitude and direction, the resultant of these two forces can be plotted. If this resultant were then extended to cross the vertical center line of the head pulley, the point at which it crosses is the pole height. Any change to pulley diameter or belt speed will change the value of the centrifugal force and, hence, the pole height.

By analyzing the forces in this way it is possible to set the speed limitations for both high and slow speed elevators. The pole height ratio is the ratio of pulley radius plus bucket projection to pole height.