| An analysis is presented of the flow force acting on a two-way valve using the equilibrium condition of the piston and the equilibrium condition of fluid in the control volume. Three types of flow forces are identified: pressure-difference-induced flow force, viscous-shear-induced flow force, and momentum-induced flow force. Nondimensional analysis shows that among all steady flow force the pressure-difference-induced flow force is largest with viscous-shear-induced flow force the second and momentum-induced flow force the smallest. However, the fluid inertial-induced flow force, which is a momentum-induced flow force, is very important while the pressure transient effect caused by the slight compressibility of the fluid is negligible.;A pressure-wave generation system has been designed and built with a novel square pressure-wave generator. By turning the square pressure wave generator sustained by the variable-displacement axial piston pump, a square wave can be generated to actuate the two-way valve with fixed piston. Simulation results shows that by taking the difference between the total flow force and steady flow force, the pressure transient effect can be observed.;The first experiment is conducted on a two-way valve with extremely low leakage. The trial test on a hydraulic circuit without pressure wave generator shows that the sound wave phenomenon is very strong and there is a pressure gradient in the vertical direction. In order to reduce the influence of the two characteristics mentioned above, the 100-points average technique and pressure profile factor is introduced, and the pressure transient effect is proved to be true.;The second experiment is conducted on a two-way valve with longer valve length, stepped housing and larger clearance. Those geometry modifications are made to reduce the energy that could be reflected at the ends and reduce the pressure gradient in the vertical direction. The usefulness of those modifications is proved experimentally. Furthermore, the influence of different damping length and non-metering length is tested and it is shown experimentally that the non metering length will have a impact on the transient flow force. The reason for this influence can be partially explained by Computational Fluid Dynamics (CFD) computation. The fluid in the non-metering section will be involved in the transient flow. And the birth of vortices will make the assumption that the fluid is moving as one chunk of fluid not valid. |
