Vortexing problems can affect all kinds of centrifugal pumps -- including self-priming pumps and submersible pumps. Vortexing occurs when water being drawn into a suction line (or into the suction fitting in a submersible pump) results in a depression in the surface of the water, often forming a visible whirling vortex -- just like what one would ordinarily see in a draining sink or bathtub. However, a vortex leading into a pump can cause the pump to entrain air, since air is easier to pump than water, and thus cause the pump to operate inefficiently and at a reduced performance condition.
Vortexing is well-illustrated here:
Vortexing can be solved by increasing the minimum submergence between the suction point into the pump and the water surface elevation, or by changing the velocity of the water entering the pump, as through the application of a flared suction line or by changing the operating speed of the pump. Please feel free to contact us with your questions.