Kroulík M., Hůla J., Rybka A., Honzík I. (2016): Pneumatic conveying characteristics of seeds in a vertical ascending airstream. Res. Agr. Eng., 62: 56-63.Pneumatic conveying characteristics were measured in vertical tubes for seeds of selected varieties of cereals, wide-row crops, oil crops, legumes and catch crops. The measured values were used for graphical representation of variation curves for the chosen groups of seeds. The values of the critical air velocity for seeds (velocity of seed lift) were computed. Statistical significance of differences in the mean values of critical velocities of tested seeds was determined. The critical velocity of cereal seeds ranged from 8.03 to 10.54 m/s. Among the crops grown in wide rows the highest critical velocity of seeds was found out in maize (13.29 m/s), the lowest in sunflower seeds (8.38 m/s). In oil crop seeds, the lowest critical velocity was recorded in poppy (4.67 m/s), which was the lowest value of all seed samples of the tested crops. The highest value of the critical velocity was measured in pea seeds (14.85 m/s).Keywords: sowing machines; aerodynamic properties of seeds; variation curves Aerodynamic properties of seeds represent the behaviour of seeds in airstream. They are mainly related to seed properties (weight, shape, surface), and also to the condition of the air environment -airflow evenness (Srivastava et al. 2006). The knowledge of aerodynamic properties of grains is applied to the design of grain cleaning and sorting systems as well as to the construction of the pneumatic sowing mechanism of seed drills.The seeds placed in a central hopper of the seed drill are sliding by gravity and by help of an opener to a vane turnstile that delivers them fluently to the airstream from the fan. The seeds are then conveyed by the airstream pressure usually in a vertical direction upwards to a distribution head and then horizontally or obliquely through delivery tubes to drill coulters.The vertical delivery of seeds upwards is a limiting feature for the appropriate function of the sowing mechanism; it is possible only when the volume flow rate of air (m 3 /s) and its velocity (m/s) are chosen in such a way that the airstream will convey the seeds evenly. This air velocity should be higher than so called critical velocity of seeds (velocity of seed lift) and should include a reserve for the potential increased mass flow of seeds associated with the required change in specific seeding rate. The upper limit of the air velocity is a requirement to avoid seed damage in the course of its conveyance.It follows from the experiments conducted in the past (Neubauer et al. 1986;Páltik et al. 2003) that the air velocity (v a ) in the vertical duct should be chosen in the range: 56

A mechanical pruner serves for pruning new hopvine shoots in spring. The later yield depends on the right timing and quality of pruning. That is why hop pruning is one of the most important agrotechnical procedures. A double-disc mechanical pruner used on high trellises cannot be used on low trellises due to its large size. Abroad, for pruning hops on low trellises a specially adapted sprinkler is used (chemical pruning). With regard to the effort to minimize the chemical environmental burden, we opted for the design of the mechanical pruner. Firstly, the low trellis, mechanical pruner, and also elements used in the design of hydraulic circuit are described. Next part of the paper is devoted to the input requirements for both the hydraulic circuit and the mechanical pruner designs. Then a description of an adapted inter-axle carrier used for the experimental model of the hop mechanical pruner and of the effected field measurement follows, along with interpretation of the measured data. These data are depicted in clearly arranged graphs showing the dependency of pressure and hydraulic oil flow on the cutting disc rotational frequency.

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The article summarizes the results of a two-year research focused on separating impurities in hop picking line by means of inclined belt conveyors. Researchers designed a new version of inclined belt conveyors which were installed in one segment of a parallel hop picking line. In the other segment the current inclined belt conveyors remained. Regarding the product quality, better results were obtained with new inclined belt conveyors where the average content of impurities at the output was 7.73%, contrary to the treatment with current conveyors where the content of impurities was 12.03%. The current inclined belt conveyors had 4.8 times higher losses of hops than the new ones. The economic assessment clearly proves the use of new inclined belt conveyors to be more effective, as the return of the costs for the exchange of six inclined belt conveyors in a picking line makes only 3.13 years at a comparable or even better quality of separation.

Rybka A., Heřmánek P., Honzík I., Krofta K. (2017): Parameters of the drying medium and dried hops in belt dryer. Res. Agr. Eng., 63 (Special Issue): S24-S32.An important factor in hop growing is the process of drying. For this purpose belt dryers with follow-up conditioning are the most widespread but they are not ideal. In this respect, an analysis of the drying process was carried out in the belt dryer of Agrospol Velká Bystřice Co., Ltd. for the 'Saaz' hop variety. Drying parameters were monitored by means of fixed sensors, continuously sensing data loggers and samples taken for laboratory analysis (hop moisture, alpha and beta bitter acids, Hop Storage Index (HIS). The process of drying showed that hops are practically dry (10 ± 2.0% of moisture) already at the end of the second belt or possibly at the beginning of the third belt. It was also proved that hops are over-dried (moisture of 4 to 8%) and then they are adjusted by conditioning to the final moisture content of 8-10%. Excessive drying leads to cone disintegration, which makes any manipulation with hops for purposes of further processing difficult and results in greater losses of lupulin. The current state in the field of technology of hop drying and conditioning is not ideal. This refers to both operating costs and qualitative features of the final product. In belt dryers prevailing so far, following stationary picking lines, their drying process is directly linked to the continuous process of harvest. In belt dryers hop cones are dried at a drying air temperature of 55-60 o C for 6-8 h coming from original 75-85% of moisture to final 8-10% prior to conditioning. Bracts themselves, however, have moisture content of only 5-6%, while strigs may have a moisture content of up to 30%. Percentage of strig weight to the total cone weight (6-12%) has a great effect on subsequent moisture permeability during the conditioning of hop cones (Kořen et al. 2008). Controlled conditioning requires roughly up to a 1/3 of the total energy requirements needed for hop growing (Doe, Menary 1979). Stability of alpha bitter acids, being the key hop substance from the point of view of brewing technology, is sufficient at drying temperatures reaching up to 60°C. However, for some heat-labile substances the drying temperatures between 50 and 60°C in the final stage of drying are too high. They lead to irreversible transformations and losses. Such substances are for instance hop essential oils that are contained in the amount of 0.5-3.5%, depending on hop variety (Hofmann et al. 2013;Kumhála et al. 2013). The pilot studies showed a decrease of 15 to 25% of the overall content of essential oils present in the hops prior to drying at the current drying conditions (Kieninger, Forster 1973;Kirchmeier at al. 2005). Besides this amount, the sensory profile changes too, due to a loss of the more volatile components. With special aroma hop varieties, so called "flavour hops", whose 25Vol. 63, 2017, Special Issue: S24-S32 Res. Agr. Eng.doi: 10.17221/35/2017-RAE content and ...