The longitudinal inclination reflects the pitch and spiral diameter. The longitudinal inclination of the spiral groove is different at different radii of the groove surface, and increases with the decrease of the radius. This structural feature of helix is expressed by the ratio of pitch to large diameter of helix. According to the force analysis of particles on the longitudinal section, the moving speed of particles increases with the increase of the longitudinal inclination of the spiral groove. When the force of ore particles is balanced, it shows the longitudinal velocity of suspension movement.

At this time, it can be considered that the movement of particles occurs under hydraulic action, and the gravity factor becomes very small. Obviously, it can not be too large for the separation stability according to the density difference and enough residence time in the tank to facilitate stratification and zoning. After experimental research, the author believes that the longitudinal inclination of the outer edge of the spiral sorter is 7-10 °, and the ratio of pitch to diameter is 0.4-0.5.