Correction Factors for Center Pivots with End Guns

Abstract

The end-gun discharge of center pivots is expressed as a ratio of the inflow at the pivot. Using this ratio, equations are developed for the friction correction factor and pressure distribution factor. If end-gun discharge is reduced to zero, then these equations reduce to the well-established equations for the friction correction factor and pressure distribution factor. For an end-gun ratio of unity, the friction correction factor also becomes unity, reflecting that the lateral is in fact a pipeline without outlets. The pressure distribution factor becomes linear, reflecting that head loss varies linearly with length. For a lateral of constant diameter and typical end-gun discharge there is a significant increase in head loss due to friction. However, there is insignificant difference in the estimate using either this technique or the effective radius technique. The pressure distribution factor is slightly higher, indicating that in laterals with end guns the pressure head toward the center of the lateral is higher. The equations presented can be used to design center-pivot laterals with end guns or the first segment of a tapered center-pivot lateral.