Nay Zar Aung

Reducing the steady flow force acting on the spool by using a simple jet-guiding groove

Reducing the flow induced forces acting on the spool is necessarily important for the energy efficient operation and minimizing the stability problem in different types of spool valves. Aiming to reduce the steady flow force acting on the spool, a simple jet-guiding groove is proposed. It is V-groove created on the side face of the spool land. By means of Computational Fluid Dynamics (CFD) simulations, the effectiveness of proposed jet-guiding groove is analyzed at various spool strokes and depths of the groove. The port width to spool stroke ratio is varied in the range of 0.1-0.5. The ratio of land face depth to groove depth is varied as 0.125, 0.25, 0.5 and 1. The results show that compared to the traditional spool, the spool with jet-guiding groove can proportionally reduce the steady flow force at every spool stroke. The deeper the depth, the more effective the jet-guiding groove in reducing flow force. Providing the same flow control capability as the traditional spool and other multiple advantages, the spool with jet-guiding groove can reduce the power requirement in operation.

Structural optimization and characteristics analysis of innovative flapper shape in a flapper-nozzle pilot valve

Cavitation in the flow field and the resonance of armature-flapper assembly are two main possible mechanisms for the self-excited noise in flapper-nozzle pilot valves, which can greatly deteriorate the performance of the valves. In our previous attempt, it has been shown that compared to traditional flapper shape, rectangle-shaped flapper is more effective to reduce cavitation in the flapper-nozzle pilot valve. However, it is necessarily important to obtain the same structural properties as traditional flapper shape. To achieve this aim, structural optimization of the innovative flapper shape is performed. Then, the static and dynamic characteristics of the armature-flapper assembly using different flapper shapes are studied numerically using a validated numerical model. The simulated static and dynamic characteristics of the optimized innovative flapper shape agree well with that of the traditional one. Thus, an effective flapper shape which can reduce cavitation as well as maintain the original mechanical performances is proposed.