Design of adjustable equivalent aperture disc filters and its hydraulic performance

A disc filter is one of the key components in micro-irrigation systems, and plays an important role in filtering impurities and reducing clogging of emitters. However, the disc filter cannot fully meet the filtration requirements of different impurity particle sizes, due to a single type of discs and a narrow range of sand grain sizes for filtration. In this research, a disc filter with an adjustable filter mesh size was proposed to reasonably change the tightness between discs. The disc filter also met the filtration requirements in the different ranges of impurity particle size, in order to reduce the manufacture and operation costs. A series of tests was carried out on the hydraulic performance of disc filters with different mesh. Five flow rates of 10, 15, 20, 25, and 30 m³/h were then set to test the head loss in the conditions of clear water with different mesh sizes of disc filters. In addition, the head loss and sand interception of disc filters were evaluated with different mesh numbers under different grades and contents. Three grades were selected as the small, medium, and large sandy water with less than 75, 75~150, and 150~300 μm sand particles and three sand contents of 0.8, 1.0, and 1.2 g/L. The results show that: (1) Different objectives of mesh filtration were achieved to adjust the disc tightness. Three types of discs were used to obtain 7 levels of tightness under three motor pressures, corresponding to filter mesh sizes of 50, 60, 75, 100, 120, 150, and 200. (2) There were some differences in the head loss dynamics and sand interception of the 7 mesh disc filters. In small graded sandy water, the 200-mesh disc piece shared the largest peak head loss, where all maximums were stabilized at about 16 m. The sand interceptions of the 200-mesh disc were 54, 73, and 84 g, which were significantly larger than that of others (P<0.05). In intermediate-graded sandy water, the head loss was greater than for 120, 150, and 200 mesh discs, with the maximum exceeding 6 m. The sand interceptions for 120 and 150 mesh discs were 72, 92, and 103 g, and 81, 92, and 95 g, respectively, which were significantly greater than that of the others (P<0.05). In large grades of sandy water, the 50, 60, 75, and 100 mesh discs all shared greater sand interceptions and increased head loss. (3) The optimization configuration of the filter mesh size was achieved using the TOPSIS. Therefore, a 200-mesh disc should be chosen in small graded sandy water. A 120-mesh disc should be chosen in intermediate-graded sandy water when the content was high, and a 150-mesh disc should be chosen when the content was low. A 50- or 60-mesh disc should be selected in large grades of sandy water when the content was high, and a 75- or 100-mesh disc should be chosen when the concentration was low. The best filtration was achieved to effectively avoid the hidden danger of head loss surge. The finding can provide a strong reference for the rational selection and use of disc filters under different sand contents in micro-irrigation systems, in order to reduce the head loss of the filter