**4. Conclusions**

(1) Orthogonal test results show that various geometrical slot parameters affected pump performance. Under small flow conditions, the factors most intensely influencing the pump head were slot width *b*1 > slot deflection angle β > slot depth *h* > slot position *p*. The factors most intensely influencing the pump efficiency were slot depth *h* > slot width *b*1 > slot deflection angle β > slot position *p*. The main factors influencing the pump head and efficiency under rated flow conditions were slot width *b*1 and slot depth *h*, whereas the main factor influencing the pump head and efficiency under large flow conditions was slot position *p*.

(2) The orthogonal test results also indicate that under low flow conditions and rated flow conditions, the head and efficiency of the pump decreased as blade slot width increased. These effects were linear.

(3) Different combinations of slot geometric parameters in Case 1 were found to increase the pump head at the small flow condition point as well as the efficiency and head of the pump at the large flow condition point compared to the original model without slots. The internal flow field shows that slotting near the front edge of the blade improved the low-pressure region of the impeller inlet flow passage and brought the flow velocity distribution in the impeller field under the large flow conditions closer to the desired value as the flow velocity distribution grew more uniform.

(4) To improve the performance of the pump, optimal slot parameter combinations according to the actual machining precision might include a small slot width *b*1, slot depth *h* of 14 *b*, slot deflection angle β of 45–60◦, and slot position *p* close to the front edge of the blade at 20–40%.

**Author Contributions:** C.W. performed the writing—reviewing and editing; H.W. made the investing; B.L. performed the data curation; C.H. made the software; L.L. made the methodology. All authors have read and agreed to the published version of the manuscript.

**Funding:** This work was supported by the National Natural Science Foundation of China (Grant No. 51609105), Changzhou Sci&Tech Program (Grant No. CJ20190048), Jiangsu Province Graduate Practice Innovation Project (Grant No. SJCX18\_0743).

**Acknowledgments:** In this section you can acknowledge any support given that is not covered by the author contribution or funding sections. This may include administrative and technical support, or donations in kind (e.g., materials used for experiments).

**Conflicts of Interest:** The authors declare no conflict of interest.
