# Influence of Cutter Head on Cavitation of Non-Jammed Submerged Grinder Pump
## 4 Numerical Results and Analysis
### Determination of the Number of Cutter Heads
#### 4.2.1 The Effect of the Number of Cutter Heads on the Performance of the Submersible Grinding Pump  
Figure 14 shows the performance of the grinding pump when the number of moving cutter heads was 2, 3 and 4, respectively. It can be seen from the figure that under the same flow rate, the higher the number of moving cutter heads, the higher the pump head. This phenomenon occurred at each operating point, and the head of different cutter heads differed greatly under low flow conditions. This was mainly because with increases in the number of cutter heads, increasing the displacement at the pump inlet will increase the hydraulic loss; the cavitation of the cutter head at the grinding device is intensified and the loss at the grinding device is increased, resulting in a drop in the head of the submersible grinding pump.  
It can be seen from Figure 14 that the shaft power of the grinding pump increased with increases in the flow rate; The shaft power of the grinding pump rose with increases in the number of moving cutter heads. The three shaft power curves were approximately parallel. The shaft power of the three-cutter head grinding pump was about 520 W larger than that of the two-cutter head pump at each working point. The shaft power of the four-cutter head grinding pump was higher than that of the three-cutter head grinding pump at each working point. The shaft power of the grinding pump was about 510 W. This is because the moving cutter head needs to consume a certain amount of power when it rotates with the shaft, and increases in the number of cutter heads will increase the hydraulic loss. Therefore, the number of grinding pump cutter heads has a great influence on the power of the pump shaft, which will cause sharp increases in the pump shaft power.  
It can be observed from Figure 14 that the flow rate was around 21 m\({}^{3}\)/h when the efficiency of the grinding pump with different numbers of cutter heads reached the highest value. The highest efficiency of the grinding pump with two, three and four cutter heads  
Figure 14: Pump performance curve with different numbers of cutter heads.  
Figure 13: Moving cutter head with different numbers of cutter heads. (**a**) 2 cutter heads, (**b**) 3 cutter heads, (**c**) 4 cutter heads.  
was 27.91%, 23.05% and 20.34%, respectively. The efficiency decreased as a whole with increases in the number of cutter heads at each working point--especially the highest efficiency point. With regard to the pump head, it dropped to a certain extent with the increases in the number of cutter heads. The drop was larger under the condition of low flow. The shaft power of the grinding pump was about 520 W larger, and the shaft power of the four-cutter head grinding pump was about 510 W larger than that of the three-cutter head grinding pump; the efficiency of the pump decreased as a whole with increases in the number of cutter heads at each operating point. It can be seen that the number of cutter heads in the grinding pump moving cutterhead had a great effect on the performance of the grinding pump. With increases in the number of cutter heads, the power of the grinding pump will increase and the efficiency will decrease. Therefore, under the premise of ensuring the cutting and grinding effect, the number of cutter heads should be selected to be as low as possible.