Approach-flow skewness and the resulting circulation have a controlling influence on free surface vortices in spite of adequate submergence. The recommended minimum submergence given here is for a reasonably uniform approach flow to the pump suction bell. Highly non-uniform approach flows will require the application of vortex suppression devices.
Experimental analysis and field experience have resulted in the following empirical relationship:
S = D + 0.574Q/D1.5 Where S is submergence in inches D is bell diameter in inches Q is rate of flow in gpm
S = D + 0.574Q/D1.5
Where S is submergence in inches
D is bell diameter in inches
Q is rate of flow in gpm
The required minimum submergence can also be determined from figure 9.8.26B taken from ANSI HI 9.8-1998 Pump Intake Design.