| A significant part of the emulsion pump station system is unloading system. For some reason such as large instantaneous flow and long pressure holding time, the electromagnetic unloading valve has been widely accepted as the core component of unloading system for purpose of pressure control and overload protection. Even if National coal industry standards MT/T188.3-2000 Mine Emulsion Pump Station-technical Condition of Unloading Valve has put forward technical requirements, test methods as well as inspection rules about unloading valve clearly, it seems that some accidents are still inevitable because of various reasons, resulting in instability and unreliability of pump station work. Thus, this paper focuses on the problem of cavitation erosion and discusses its related aspects including pressure and gas phase distribution of main valve chamber to do research into flow channel optimization of unloading valve.That is to say, based on the background and significance, the study firstly shows the main failure modes of the electromagnetic unloading valve. According to the research status and existing problems about cavitation erosion all over the world, it can be concluded that the analyzing of unloading valve’s cavitation erosion plays a pivotal role in current study.It is argued that some problems like internal cavitation and the damage caused by cavitation will appear if unloading valve has been utilised more than 1500 hours in the case of mechanic unloading work. Besides, the steel inner wall between four outlet holes along the surface of the main valve sleeve will be almost eroded. Therefore, the article tends to establish the simulation model of mechanic unloading so as to illustrate inlet and outlet pressure characteristics, inlet flow characteristics as well as displacement of the main valve/pilot valve of the unloading valve by connecting the theory and the practical matters from enterprises. In the meanwhile, the impact of pilot valve seat diameter, main valve cone angle and main valve cone diameter these three structure parameters on the inlet and outlet pressure fluctuation range of the unloading valve will also be illustrated in the thesis by combining with individual functions of each part.The findings reveal that low-pressure in valve port back will appear when there is a opening small valve, leading to the producing of gas bubble by applying fluent flow field simulation software and cavitation model, the AMESim and the flow field pressure, flow velocity and gas phase distribution of main valve with different size of valve opening. Additionally, the following bubbles with emulsion can form the cavitation flow. Such flow could be blocked by inner walls between outlet holes. Bubbles then collapse gradually so that the cavitation erosion in the surface of surrounding parts would become evident through the separation of materials. Obviously, these two methods are found to produce the same result after the comparison of flow simulation and the destroyed objects due to cavitation erosion.In view of the reasons about cavitation appearance in the valve chamber, we prefer to start with the promotion of valve port’s back pressure and the extension of cavitation flow’s movement. Following the first part, the paper also suggest the relevant optimization plan for mechanical construction and control system. After that, by comparing before-and-after parameters of flow field pressure, gas phase and velocity, it can be found that optimization measures not only have a great effect on cavitation weakening, but also extend the useful life of unloading valve effectively, thereby reducing the frequency of replacing unloading valve and improving its productivity.Overall, the purpose of this report is to demonstrate reasons for cavitation in the main valve chamber and the improving measure of valve chamber’s design on the basis of AMESim and Fluent. In part, the evidence could provide guidance about cavitation mechanism for other authors and also become the reliable source of hydraulic valves to be referenced. |
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