2.25. Coefficient of Friction. Granular materials Will not flow through pipes or chutes unless the pitch is sufficient to overcome the coefficient of friction of the material upon the conduit. This characteristic determines the minimum pitch of conduit intended to move materials by gravity.
Grain or other granular material will flow in a conduit at a flatter angle if it is moving when introduced into the conduit. If a system is designed on this basis, trouble may arise from accidental stoppage since starting flow may be cliflicult if a minimum pitch is used. Coefficient of a few grains are listed in Table 2.5.