Research on sprinkler irrigation is developing toward the low pressure spray. When the fixed rotary sprinkler works at the low pressure, there is too much water concentrating at the end of jet, causing seriously uneven water distribution. In order to solve this sprinkler irrigation problem, an aeration jet method is put forward in this paper. Based on the structures of impact sprinkler PY20, a gas suction component is adopted to form an aeration impact sprinkler. The axis of gas suction pipe coincides with the axis of sprinkler tube. The environmental gas is sucked into the impact sprinkler due to the negative pressure formed by jet flow. Performances of PY20 impact sprinkler with and without aeration were compared under the same conditions of working pressure, trajectory angle, flow rate of the sprinkler, and the effect of sub-nozzle has not been taken into account.. The comparison parameters include the ranges of jet, water distribution curves along the radial direction, coefficients of distribution uniformity for square combination with spacing factor equal 1, droplet size distribution and so on. The experiment finds that the outlet diameter of original impact sprinkler is 7 mm; when 2 mm inner diameter gas pipe is installed, the outlet diameter should be changed to 8.3 mm for the aeration impact sprinkler to keep the same flow rate with the original impact sprinkler. Two types of sprinklers nearly have the same jet range under the same working pressure. The negative pressure of gas pipe is measured by U-gauge, and the height difference of mercury column increases with the impact sprinkler working pressure, which means that the intake capacity becomes stronger as the working pressure increases. As the working pressure reduces to 100 kPa, the aeration sprinkler still has the ability of gas suction and it has 76 mm height of mercury column. The aeration method improves the water distribution curve at the middle jet range, and it makes water distribution line a litter higher at the middle jet range, while a little lower at the end of jet range. In order to compare the aeration impact sprinkler with original impact sprinkler when they are used in combination sprinkler irrigation, and to make sure whether the aeration method can improve the uniformity of water distribution or not, the square combination with spacing factor equal 1 is selected to do a test. For the combined 4 sprinklers, its radial direction water distribution curve is overlapped through linear interpolation. At the working pressure of 200 kPa which is lower than national standard, the coefficient of distribution uniformity (CDU) is enhanced from 62.8% to 68.8% by the aeration method. Experiments are also done by using laser raindrop spectrometer. The raindrop size distribution produced by aeration impact sprinkler and original impact sprinkler is compared at the location of jet end and at the middle of jet range. At the middle jet range, the aeration impact sprinkler has a much larger median diameter of water accumulation frequency than impact sprinkler, while it has the smaller diameter at the end of jet range. It can be proved that the gas sucked into the jets changes the spray droplet size distribution. The experimental results in this paper prove that the aeration impact sprinkler is feasible for applying to agricultural irrigation. There are many further investigations which need to do, such as how the aeration sprinkler performance changes with the gas flow rate, and the lowest working pressure and the optimized structure for aeration sprinkler need to be studied. © 2016, Editorial Department of the Transactions of the Chinese Society of Agricultural Engineering. All right reserved.
