Substantiation of the Type of Air Switchgear of Pneumomechanical Seed Drills
Authors:   Central Ukrainian National Technical University, Osypov Ihor 
Published: April 2021

Fulfillment of requirements of agrotechnics on uniformity of distribution of seeds on the area of feeding completely depends on the correct choice of a design of sowing system. Promising development of designs of row seeders is the use of pneumatic sowing systems, which is a prerequisite for increasing productivity and reducing direct costs during sowing. But, in some cases, such a technical solution leads to an increase in metal consumption of drills, complicates their maintenance. The costs of production and operation of such drills become unjustified. Various types of air switchgears are used to select air from sowing machines in vacuum pneumatic sowing systems and to distribute it over sowing machines in pneumatic sowing systems of excess pressure. Recently, in the designs of most pneumatic seeding systems of domestic and foreign drills used receiver, which has the form of a pipe, the inner cavity of which is connected to the fan. Air ducts of the same length connected to the sowing machines are adjacent to the outer side surface of the receiver. The use of the receiver simplifies the design of the pneumatic seeding system, eliminates the difference in the lengths of the air ducts and reduces their length, which eliminates their inflections in the process of the drill. The conducted researches allowed to establish the dependences, the analysis of which showed that with increasing the number of seeders the unevenness of the differences in the sowing machines increases, which leads to the unevenness of sowing the seeds. For drills with a collector, this is explained by the fact that with increasing uniformity, the variation of air duct lengths and pressure losses in them increases. In this case, an increase in the coefficient of variation of the non-uniformity of propagation is observed when the coefficient of hydraulic resistance of the sowing machine decreases, since its value becomes comparable with the coefficient of hydraulic resistance and the non-uniformity of lengths. As the coefficient increases, the effect of the unevenness of the air duct lengths weakens due to the decrease in the fraction of air duct resistance in the total resistance of the pneumatic system. For drills with a receiver, the variation in the level of rarefaction in the receiver increases with increasing uniformity, which leads to uneven distribution in the sowing machines. At the same time, a decrease in the coefficient of variation is observed with an increase in the diameter of the receiver and an increase in the coefficient of hydraulic resistance of the sowing machine. The revealed dependence finds its physical explanation in the fact that the increase in the cross-sectional area of the receiver and the reduction of air flow in the seeder leads to a decrease in air flow rate in the receiver, providing a decrease in the amount of air connected to the. Therefore, the static pressure along the entire length of the receiver is equalized. The analysis of dependences also shows that seeders with a receiver with a diameter of more than 70-80 mm have advantages over seeders with a collector in terms of air selection from seed drills. As the previous diameter of the receiver increases, this advantage becomes even more noticeable.