Occasionally, annular seals of ball valves in hydro power plants may not perform their sealing function adequately but develop periodic vibration with periodic leakage rates causing high amplitude pressure fluctuations in the penstocks. The aim of the present study is to develop a simplified model that can explain the excitation mechanism and estimate the behavior of the hydro-mechanical system depending on the geometrical and physical parameters. The stability of the system has been studied in order to yield recommendations for best operating conditions. The governing equations are nonlinear and the perturbation technique has been adopted to solve the system variables. Following, a dimensionless analysis was developed to gain more knowledge on the parameters affecting this phenomenon. A MATLAB code was designed and implemented to study the system stability for different input reservoir energy levels and different system configurations. The results show that the system stability depends on the relation between the main line inertia and the leakage kinetic energy, the leakage reduced velocity, the seal surface area ratio, the pilot line geometry and the hydraulic losses. Also, solving the hydro-mechanical model nonlinearly brings about oscillation amplitudes that exceed the gap clearance as it is very small and the seal will hit the ball surface going backward and forward.

有时，水力发电厂中球阀的环形密封件可能无法充分发挥其密封功能，但会产生周期性振动，并具有周期性泄漏率，从而导致压力管道中的高振幅压力波动。本研究的目的是开发一个简化的模型，该模型可以解释励磁机理并根据几何和物理参数估算液压机械系统的行为。已对系统的稳定性进行了研究，以便为最佳操作条件提供建议。控制方程是非线性的，并且已经采用摄动技术来求解系统变量。随后，进行了无量纲分析，以获取有关影响此现象的参数的更多知识。设计并实施了MATLAB代码，以研究不同输入油层能量水平和不同系统配置的系统稳定性。结果表明，系统稳定性取决于干线惯性与泄漏动能，泄漏降低速度，密封表面积比，先导管线几何形状和水力损失之间的关系。同样，非线性地求解流体力学模型会导致振荡幅度超过间隙间隙，因为它非常小，并且密封件会前后撞击球表面。密封表面积比，先导管线几何形状和水力损失。同样，非线性地解决流体力学模型会导致振荡幅度超过间隙间隙，因为它非常小，并且密封件会前后撞击球表面。密封表面积比，先导管线几何形状和水力损失。同样，非线性地求解流体力学模型会导致振荡幅度超过间隙间隙，因为它非常小，并且密封件会前后撞击球表面。