Studies On The Mechanical Characteristics Of Flap Valve Cutoff Device In Pumping Stations

Along with the progressively advancement of China's South-to-North Water Diversion Project and construction and technical innovation of large pumping stations, the demands in operation safety and energy-saving are becoming higher and higher. In pumping station engineering, if the cutoff devices are improperly designed, the stopping of pump units especially accident stopping caused sudden power off will cause water back flow and reverse rotating of pump sets. If the situation is more serious, the pump sets may be damaged, causing accidents and influencing the normal operation of pumping systems. Therefore, the research on cutoff devices in pumping stations has become an important task. Flap valves are the main cutoff devices widely used in pumping stations, which are simple in structure, convenient in maintenance, less investment and easy to start. However, there are two disadvantages with flap valves. One is the greater hydraulic loss caused by their own weight of flap valves, and the other is the impact force under the action of water pressure and the flap valve itself in pump stopping, endangering the safety of hydraulic structures and flap valves. In order to guarantee the safety operation of pumping station with high efficiency, it is necessary to investigate systematically the mechanical characteristics of flap valves.Based on the actual working conditions of flap valve in pumping stations, and starting out from the basis theory of fluid dynamics, the opening process of flap valve and forces acting on it are analyzed, the opening angle calculation formula of flap valve are derived, and the movement rules of flap valve in various conditions are established. Considering the effect of collision and impact factors, mathematics models for various kinds of flap valves are established, and the calculations of impact force and the force on hinges under specific conditions are discussed. Combining with the dynamic characteristics of pumps stopping, nonlinear analyses of flap valve's falling movements are carried out when the pump rotates in normal direction and water flows from sump to discharge pool and the pump rotates in reverse direction and water runs from discharge pool to sump, and a formulate calculating the falling impact force of flap valve is proposed. The stress wave method is applied for the first time to investigate the fir impact of flap valve, and the time duration of first impact and the maximum impact force are calculated, and the rules of force acting on the flap valve in the first impact are analyzed as well. By means of model test with different specific weights of flap valve materials, the relations of opening angle with hydraulic loss and flow rate are analyzed and researched. The working conditions of prototype flap valve are predicted with the help of affinity theory, thus providing reliable theoretic basis for the technical innovation of flap valves. A new type of air-filled floating flap valve is developed, which can regulate automatically the float weight of flap valve under water. The hydraulic loss and impact force are effectively reduced, and the two problems mentioned-above are solved systematically, having important theoretic and application value.