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Mesh filters are frequently employed in water-saving irrigation fields. Studies addressing the method of cake formation and the characteristics of the cake during the mesh filter's growing phase are still missing. One-way and orthogonal experiments were carried out using mesh filters with 220 μm and 320 μm aperture sizes as the research objects, taking particle concentrations, inlet flow, and growth phases as experimental factors. According to the variation rule of seed pressure drop in the formation process of filter cake, the growth process of filter cake is divided into four stages, which are as follows: slow blockage first and second stages (M1, M2), fast blockage stage (M3), and filter cake filtration stage (M4). Moreover, the size distribution, porosity (ε), pore-to-particle ratio (KP), and median size (d50) of the filter cake were used to represent the structural characteristics. The results show that the growth of filter cake was a process that started with the filling of mesh pores by intercepted particles and progressed to the filling of large-particle skeleton pores by subsequently filtered particles. During this process, the proportion of intercepted particles gradually decreased, while the proportion of filtered particles increased incrementally, and the median size (d50) and porosity (ε) decreased. Meanwhile, the smaller the aperture size of the screen, the smaller the filter cake's median size (d50) was, but the larger the pore-to-particle ratio (KP) was. As the flow rate increased, the porosity (ε) was augmented in the M1 and M2 stages; however, it decreased in the M3 and M4 stages. The concentration had a minor influence on the filter cake's porosity. Lastly, the regression model for filter cake porosity under two aperture size conditions was established, based on factors such as flow rate, concentration, and growth stage. The coefficients of determination, R2, for the model were 90.33% and 80.73%, indicating a good fit. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]