EYE OF THE IMPELLER E021
In determining the area of the suction eye, the area occupied by the impeller shaft hub is deducted. The hub is the central part of the impeller which is bored out to receive the impeller shaft.
The inlet flow angle at the eye of the impeller will affect the efficiency and the net positive suction head required of the pump. The angle is normally selected between 10 degrees and 25 degrees with 17 degrees being the most common.
For the best pump efficiency, the angle should be larger.
For a lower net positive suction head required (NPSHR) it should be smaller.