Abstract
The best velocity in the spiral casing the section of which is circular may be found by the equation Aλ+Bλ^<3/2>-1=0, where λ is the coefficient of casing velocity. This equation can be represented by a diagram which for all practical purposes may be used to determine the best casing velocity with an error of ±4 percent in the worst case, which can be corrected more accurately, if desired. The range of merit of making the throat conical can be determined by the equation Aλ^2+0.83Bλ^<5/2>-2λ+∧_<k=1>=0. This is also represented by a diagram, by which the limit of selection of the casing velocity for a certain area ratio of the conical throat can be known.
