A numerical method and an experimental analysis were applied to obtain a better understanding on the characteristics of cavitation inside the non-circular opening spool valve with U-grooves. The relationship between structural parameters and cavitating flow inside the valve, as well as acoustic noise, are studied. A two-staged flow resistance model was brought forward for the qualitative prediction of the cavitation intensity and incipient cavitation number inside the valve. The throttling effect of the first throttling stage plays an important role in the incipience and development of cavitation inside the valve. The reduction of pressure loss caused by the first throttling stage benefits to the cavitation resistance. With the decrease of cavitation number, the acoustic noise level increases until the former reaches the critical value (σ = 0.04). Once cavitation number is below the critical value, the flowrate of the valve is choked, and the acoustic noise level decreases instead.
After second oil shock in 1978, fuel consumption cost has become an important evaluation factor for construction machinery, many improvements have been made to increase machine efficiency[1]. Recent year, as the Kyoto Protocol get effective, further effort on fuel consumption cut or CO2 cut is required for all machine makers. As the success of the hybrid system in automobile, construction machinery makers also put a lot of force on research to apply the hybrid concept in their own machines. This paper introduced the research and development of hybrid machinery in Hitachi Construction Machinery Co. Ltd , and also discussed the problems in this field.
Cavitating flow in non-circular opening spool valves with U-grooves has been investigated in this article. Multifarious cavitating properties, including acoustic cavitation, morphologic cavitation, and discharge performance with cavitation, are investigated, the correlations of which are discussed. The critical opening condition in each valve is obtained based on the analysis of a throttling model. It is found that the cavitating properties show remarkable differences in the two situations when the opening is larger and smaller than the critical opening. Additionally, cavitation impacts on the discharge performance are investigated with the assistance of acoustic and visual detection.
This paper presents predictions and measurements of the structures of cavitation flow inside the throttling valve. The three-dimensional Navier-Stokes equations in a moving reference frame are solved on tetrahedral meshes. A sliding mesh technique is utilized to characterize unsteady interactions. The accuracy of the predicted flow fields is evaluated by comparison to measurement results taken with a high-speed camera. Results show that the pressure distribution inside the throttling groove is sensitive to the valve port configuration and flow direction. Bubbles form near the side wall of the groove on the throttling edge where, in the case of flow into the throttling groove, the pressure is at a minimum. With the increase of the pressure gradient bubbles saturate the flow. Noise spectrum analysis indicates that the noise level induced by cavitation is determined by the number and size of the bubbles passing through the valve grooves.
Load sensing concept and general control scheme are not new and it has been widely applied for may industrial hydraulic systems. Fluid Power. Edited by T. Maeda.
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