Performance analysis and test of valve-regulated proportional fertilization pumps

Abstract: The valve-regulated proportional fertilization pump (proportional pump for short) is a kind of fertilization equipment with excellent performance, but it can't be widely used due to complicated structure and high manufacturing requirements. At present, most of proportional pumps sold in domestic market are imported from developed countries, and due to the complex structure and difficult production, most of the proportional pumps produced in China are mainly imitated. Meanwhile, there are many researches on the proportional pump in China, but its structure is still complex and price is still expensive. Therefore, it is very meaningful to study the performance of a proportional pump with high precision and simple structure. Firstly, in this study, a simple structured valve-regulated proportional fertilization pump was introduced. This proportional pump does not require an external driving device, taking advantage of water pressure to cause a pressure difference between the two sides of driving piston, driving the piston moving periodically and making use of the reversing mechanism to realize travel conversion, so that the driving piston periodically reciprocates and drives the fertilizer injection piston fixed on it. It can switch between irrigation mode and irrigation and fertilization mode by adjusting the three-way valve. Secondly, the internal structure, main performance parameters and principle of valve-regulated proportional fertilization pump were analyzed comprehensively. Furthermore, in order to verify its hydraulic performance, tests were carried out. Energy conversion efficiency, fertilization ratio, and fertilization ratio stability were taken as the main performance indicators. The results showed that when the pressure difference between inlet and outlet was constant, the inlet flow rate decreased firstly and then increased with the three-way valve angle of the proportional pump increased, showing same trend under all pressure differences between inlet and outlet. The main reason for this trend was that the inlet flow cross section of the three-way valve decreased first and then increased, reaching the minimum when the three-way valve angle was 40°-45°. At the same time, since the three -way valve angle was between 15 ° and 75 °, the energy loss was caused by mechanical mechanism, so the curve of relationship between three-way valve angle and inlet flow under different pressure differences between inlet and outlet was basically symmetrical about 45 °. The fertilization ratio of the proportional pump was proportional to the horizontal split ratio of the three-way valve, and the fertilization ratio could achieve continuous changes in the range from 0.07% to 0.35%. The fertilization ratio gradually decreased as the pressure difference between inlet and outlet increased. The theoretical calculation value of the fertilization ratio was 0.36% when all incoming flows passed through the proportional pump, but the data obtained under different pressure conditions in the experiment were less than it. As the pressure difference between inlet and outlet increased, the fertilization ratio gradually decreased. Because as the pressure increased, the frequency of fertilizer injection piston movement increased, but the efficiency of fertilizer injection gradually decreased, that is to say, fertilizer injection insufficiency was more serious at this moment. The energy conversion efficiency increased with the increase of the pressure difference between inlet and outlet. The fertilization ratio stability of the proportional pump was 95.91%, which indicated that the fertilization ratio of proportional pump under different pressure differences between inlet and outlet was relatively stable. In the future, researches on the principle of the three-way valve adjusting the fertilization ratio need to be developed further. Firstly, its structure should be improved to reduce difficulty and improve accuracy of its control; secondly, carrying out research on structural optimization can improve energy conversion efficiency and reduce energy loss; thirdly, increasing the adjustment range of the fertilizer ratio can be realized by increasing the diameter of the fertilizer suction chamber to meet the needs of different crops; last but not the least, strengthening the sealing design will improve the withstand voltage range and volume efficiency of the pump body.