Optimizing Water Hammer Protection Strategies for Water Conveyance Systems at Floating Pump Stations Experiencing Large Water Level Fluctuations

Under large water level fluctuations, emergency pump shutdown in floating pump stations tends to induce severe water hammer oscillations, with consequences including excessive negative pressure, potential cavitation and water-column-separation risk, and uncontrolled pump reverse rotation; this seriously threatens the operational safety of water intake systems. We seek to develop an economical and effective water hammer protection strategy. Therefore, we study a long-distance water conveyance project with a floating pump station, establish a numerical model of hydraulic transient processes, and carry out a numerical simulation of a pump-trip water hammer, enacting a combined protection strategy that integrates rules on pump outlet valve closure and air vessels. Meanwhile, we analyze the regulation effects of key parameters, including air vessel volume, connecting pipe diameter, and water–air ratio (the ratio of initial water volume to initial air volume inside the air vessel), on the pipeline pressure and pump rotational speed. Overall, with the simultaneous shutdown of three pumps at the minimum operating water level, negative pressure seriously exceeds its limits in the absence of protective measures. In optimizing the valve closure rule alone, we can effectively suppress reverse pump rotation, but this fails to effectively address the issue of negative pipeline pressure. After introducing air vessels to form a combined protection system, the indicative negative-pressure severity in the pipeline significantly improves due to the synergistic effect of valve closure (suppressing reverse rotation) and air vessels (regulating the pressure). On this basis, we identify the best-performing option among the investigated cases, on the premise that a larger volume is economically unjustified, via multi-parameter comparative analysis. This consists of a two-stage valve closure rule (a 5 s fast closure duration + 80% fast closure angle + 35 s slow closure duration) alongside an air vessel with a 15 m3 volume, a 0.3 m connecting pipe diameter, and a 1:1 water–air ratio, and a terminal air valve with a 300 mm air intake diameter. This scheme balances hydraulic safety and engineering economy; the maximum pipeline pressure, minimum pipeline pressure, and maximum pump reverse speed all meet specification requirements, enabling risk control for the investigated pump-trip water-hammer conditions. These research findings provide a theoretical basis and technical support for the design of water hammer protection schemes in similar water conveyance projects at floating pump stations.