Research on Water Hammer Protection in Coastal Drainage Pumping Stations Based on the Combined Application of Flap Valve and Sluice Gate

The safe operation of drainage pumping stations, which are core flood-control facilities in eastern coastal areas of China, is paramount due to frequent typhoons and short-duration heavy rainfall. To enhance the operational safety against water hammer during pump trips caused by power failure, a water hammer protection method based on the combined application of flap valves and sluice gates is proposed. Only the scenario of all pumps tripping simultaneously was considered. A one-dimensional simulation model of the pumping station’s hydraulic transient process, which included pumps, pipelines, flap valves, and sluice gates, was established to analyze the system response under three scenarios: (i) only the flap valve closes normally, with the sluice gates remaining open, (ii) the flap valve fails, only the sluice gates operate, and (iii) the combined application of flap valve and sluice gates. In scenario (i), the maximum and minimum channel pressure heads were 13.53 m and −2.22 m, respectively, with no pump reversal occurred. However, continuous pressure fluctuations were observed downstream of the flap valve, posing a threat to the flow channel’s safety. In scenario (ii), the channel pressure heads all met the control requirements. Employing a 60 s single-stage linear closure rule for Gate #1 maintained the pump’s reverse speed within the safe range, peaking at −147.25% of the rated speed, with a reversal duration of 60 s. In scenario (iii), all channel pressure heads met basic control requirements, and no pump reversal occurred. The optimal strategy was found to be the adoption of a 60 s single-stage linear closure rule for both sluice gates. Compared to the scenario (i), the combined application reduced the amplitude of pressure fluctuations and damped these fluctuations rapidly, thus shortening the oscillation duration. The combined approach innovatively utilizes existing infrastructure for water hammer control, providing an economical and reliable solution for water hammer protection in urban drainage pumping stations.