1.Changes in hydraulic parameters: increased pressure, decreased flow, and vibration risk
Throttling effect: Reducing the water outlet of the pump is actually equivalent to closing the outlet valve of the pump. Reducing the outlet diameter is equivalent to increasing the local resistance coefficient. Following the Darcy-Weisbach formula, the system pressure will jump nonlinearly (experimental data show that a 10% reduction in diameter can lead to a 15-20% increase in pressure), while the flow rate shows a Q∝A·v attenuation law.
Although the shaft power decreases by about 8-12% with the decrease in flow, the vibration intensity caused by pressure pulsation may increase by 20-30%, especially near the critical speed, which is easy to induce structural resonance.

2. Relationship between head and pressure: Theoretical head remains unchanged, actual pressure changes dynamically
The oretical head remains unchanged: The theoretical head of the impeller is determined by geometric parameters and has no direct correlation with the water outlet diameter.
The throttling effect will increase the outlet pressure of the pump: When the system working point moves along the H-Q curve and the external environment changes (such as fluctuations in pipe network resistance), the pressure fluctuation amplitude increases by 30-50%, and dynamic prediction is required through the pressure-flow characteristic curve.