The self-cleaning screen filter is one of the most common types used in drip irrigation systems. Backwashing pressure difference and backwashing time for two screen filters with one geometry and two different screens (178 μm and 124 μm) using two water qualities (tap water and sand–water mixture) were studied in a total of 88 runs (42 runs for tap water, 22 and 24 filtration cycles for sand–water mixture and backwashing, respectively). The backwashing pressure difference and backwashing time were calculated using the experimental data, and the results were largely in the range of measured values. Three constraint conditions (flowrate, sand condition and filtration time) of backwashing pressure difference were analysed, and the optimal values of backwashing pressure difference were given as 60.0 and 70.0 kPa for 178 μm and 124 μm filters, respectively. The backwashing time of the screen filter should be an optimal value that ensures that the pressure difference between the internal and external surfaces of the screen decreased to the initial value, and the sand concentration of the backwashed outlet decreased to a small, stable value. Based on the results of the backwashing experiment and prototype observation, the optimal backwashing time was given as 30 to 45 s for both screen filters.

With the intensive and large scale application of IETM in equipment integrated support, information retrieval technology becomes one of the most key technologies. This article discusses the full-text search technology and Lucene full-text retrieval engine, and combines them to develop a highperformance scalable IETM full-text retrieval system, this system can effectively deal with IETM unstructured data and structured data, significantly improving search efficiency and it is convenient to extend and easy to maintain. First, it briefly introduces information retrieval theory, and discusses the information retrieval requirement in IETM. Then, it thoroughly surveys the Lucene full-text retrieval engine, including its framework, retrieval process and index mechanism. Next this paper designs Lucene based IETM information retrieval process. Finally, the realization of Lucene based IETM information retrieval function.

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The water volume used for blowdown of mesh filter is one of the important indicators to evaluate the economic benefit of a mesh filter. The amount of water used for drainage of the mesh filter can be controlled by setting the start-up time of the blowdown residue discharge of the mesh filter. Through the indoor prototype test, the sediment of the Manas Riverbed in Xinjiang, China was used as the filter medium to test the mesh filter and analyze the water usage volume at each stage. The test focused on the analysis of the trend of the pressure difference between the inlet and outlet of the mesh filter over the filtration time. The results showed that as the filtration time was prolonged, the inlet and outlet pressure difference of the mesh filter showed an S-shaped curve with time. The pressure difference between the inlet and outlet can be divided into 4 stages, i.e., the start of filtering to the first inflection point of the abrupt change in the pressure difference, the first inflection point of the abrupt pressure difference change to the median point of filtering, the median point of filtering to the second inflection point of the abrupt change in the pressure difference, and the second inflection point of the abrupt pressure difference change to the end of filtering. At the same time, the water usage volume for blowdown was calculated under various working conditions. This paper analyzed the start-up time of blowdown at three different time points, i.e., after the completion of the entire filtration cycle of the traditional mesh filter, at the first inflection point of pressure difference and at the second inflection point of pressure difference. The tests were performed under the condition that the filtration cycle of the mesh filter was 10 days. The results have shown that compared with the traditional screen filter that starts the blowdown at the end of the entire filtration cycle, starting the blowdown at the first inflection point of pressure difference can save 200–300 m3 of water resources for a single mesh filter, and starting the blowdown at the second inflection point of pressure difference can save 30–90 m3 of water resources for a single mesh filter. Meanwhile, the working conditions in the analyses in this paper were consistent with the actual engineering operating conditions. It is recommended that the mesh filter in the micro irrigation system can use the first inflection point of pressure difference to control the start-up time of the blowdown residue discharge, which can not only save water resources, but also ensure that the mesh filter runs at the optimal filtering conditions.

：The discharge performance of the screen filter determines the water consumption in the discharge process of the filter and the working efficiency in the next work cycle. Based on the analysis of the discharge performance of the screen filter, it is found that the sewage discharge flow and the sediment content of the inlet water are the important influencing factors. For exploring screen filter drainage effect, the focus of the experiment was on the relationship of sewage discharge cleanliness, sewage discharge time, sewage discharge flow and sediment content of a new type of rotatable plate screen filter .The results show that: the best default under differential pressure and sewage discharge flow is the core of the rotatable plate net filter factors, with the increase of sewage discharge flow, sewage discharge time reduces, sewage discharge cleanliness increases, blow down effect is remarkable. At the same time, according to the law of mass conservation, the mathematical models of sewage discharge time and sewage discharge flow, sewage discharge cleanliness and sewage discharge flow were established. According to the test results, the results show that the fitting correlation coefficient r between the calculated results and the test results can reach above 0.98 .In order to ensure that the filter can achieve high efficiency in the case of low discharge water consumption, it is recommended to set the sewage discharge flow as 180 m 3 /h and the sewage discharge time as 50 s in actual work to achieve 98% of the sewage discharge cleanliness. Key words：rotatable plate screen filter；sewage discharge time；sewage discharge cleanliness；sewage discharge flow；effect of sewage