Design And Performance Analysis On A Two-stage Self-priming Centrifugal Pump

Self-priming pump has been widely used in situations where pumps are frequently switched on or fluid is hard for irrigation. This is because the self-priming pump can fill water by self-priming, and it is small in size, easy to install and maintain. Currently, self-priming pumps are mostly in single stage, which cannot achieve high head within limited range of radical size; while multi-stage self-priming pump is right to make up this shortfall so that it can do self-priming, along with the high head. As far as we know, previous works still lack of discussion on multi-stage self-priming pumps. In this work, we develop the structure for a typical two-stage self-priming pump for sprinklers and hydraulic design the flow components of this pump; then we analyze the internal characteristics with CFD method; and finally we analyze the effects of combination cutting for impellers on the performance of pump. The following are the main results:1. This paper presented a survey for current works on self-priming pumps and multi-stage pumps and an outlook on the development tendency.2. Based on requirements for practical use,the structure of the pump was designed. The flow components of the two-stage self-priming pump including the first stage impeller, the radial guide vanes, the secondary impeller and the volute were designed with hydraulic design method.3. Internal flow of the two-stage self-priming pump was simulated with CFX and then the hydraulic performance and self-priming time tests were performed. The characteristics of the pump like energy performance, internal flow, pressure pulsation and radial force in different situations were analyzed. The simulation shows:(1) The results of the numerical simulation show that the two stage self-priming pump in design conditions can obtain a head of 107.58 meters with 60.18% efficiency, which meets the requirements of hydraulic design. Besides, the efficiency of the pump is high, when the flow range is between 0.9Qd~1.4Qd.(2) The internal flow field from the numerical simulation shows that the flow state at the outlet of return guide vane is poor, generating a large lose. Hence, we optimize the outlet of return guide vane with CFD method and the results show that the efficiency of the optimized pump increases 0.81 percent point under design condition.(3) The optimized two-stage self-priming pump was built. Then the hydraulic performance and self-priming time were obtained through experiments. The results shows: at design conditions, the test efficiency reaches 60.58%; besides, within flow range of 52m3/h~85 m3/h, the test efficiency is always above 58%. In addition, the self-priming time of the pump is 154 s, when the self-suction height is 4m.(4) Unsteady numerical simulation is introduced on the optimized pump and the internal pressure pulsation and radial force were analyzed. At large flows rates, when the vane passes through the tongue, it causes a huge instant pressure pulsation on the tongue near spiral flow path; otherwise, it’s contrast. The radical force on radical vane is notably smaller than that on spirals. Under the same conditions, the radical force on the spiral of the secondary pump is nearly the 20 times that for the radical vane of the primary pump.4. In order to adjust the application scope of the pump, the performance of outlet diameter for impeller for the two stage self-priming pumps was analyzed with a combination of CFD simulation and experimental verification. The results show the decline of outlet diameter can shift the best efficiency point to smaller flow conditions. When the diameter declines 6%, the smaller the self-priming time increases 1.7%. Hence, we can meet the use requirement by cutting the outlet diameter of impeller, when the head is between 94m~107m. when the outlet diameter of impeller is small, the radial force of the radial guide vane and the volute is small and the pressure pulsation in the radial guide vane and the volute is also small.