Hydraulic performance experiment of variable wetting sprinkler based on single-chip microcomputer

Abstract: Low pressure spraying and precise irrigation are both the important directions for the development of sprinkler equipments. Variable range sprinkler can adjust the wetted radius according to the crop distribution or field shape, realize precise spraying and decrease the energy consumption of sprinklers simultaneously, and thus accord with the developing directions for sprinkler equipments. Traditional variable range sprinklers often use the flow regulation devices to change the working pressure of the sprinkler to realize variable range spraying, however, the flow regulation devices losses hydraulic energy, leading to excessive energy consumption for variable range spraying. An open loop sprinkler irrigation system was established using the controller based on the single chip microcomputer (SCM) to solve the problem. The SCM controller was used to control the frequency output of the converter to the pump unit, in this way, the rotating speed of the pump and the working pressure of the sprinkler could be changed accordingly. As the SCM controller changed the working pressure, the wetted radius of the sprinkler changed, realizing the variable range spraying. The hydraulic performances and energy consumption of the sprinkler was investigated when the sprinkler irrigation system sprayed a square wetted area using the lawn sprinkler TORO S800. The results showed that the measured working pressure for spraying square wetted area ranged from 107 to 225 kPa, responding accurately to the theoretical curves; the wetted radius ranged from 7.6 to 10.1 m, which means that the shortest wetted radius was 0.75 times of the maximum one, meeting the requirement of square wetted area spraying; The coefficient realizing square area spraying was 97.2% in this study, higher than that (89.7% and 86.9%) using the square wetted area sprinklers with flow regulation devices; the average water application of the low energy sprinkler irrigation system was 2.8 mm/h and the maximum combination distribution uniformity of sprinkler irrigation was 77.7%, reaching the requirement proposed by GB/T 50085-2007 "Technical code for sprinkler engineering" that the uniformity of fixed sprinkler irrigation system should be larger than 75%; the optimal sprinkler spacing ranged from 13 to 14 m; the combination distribution uniformity and sprinkler spacing was same as that when the lawn sprinkler sprayed a circular wetted area at the pressure of 185 kPa. The comparison of energy consumption was taken between square wetting sprinkler controlled by SCM and circular wetting sprinkler by the index of energy consumption per unit area and unit irrigation depth under the same combination distribution uniformity. The energy consumption formula of the sprinkler was derived theoretically, showing that the energy consumption of the sprinkler was linear to its working pressure. The average pressure of square wetting sprinkler in this low energy system was 129 kPa with the same uniformity as the circular wetting sprinkler at 185 kPa, making the variable spraying for square field a 30.3% energy saving compared to the traditional circular wetting sprinkler. By using the variable spraying system based on SCM, the energy consumption can be greatly reduced.