Investigation of the Actual Value of the Vacuum Time of a Measuring Vessel by Ejector

Introduction. In industry, the process of obtaining technological vacuum using ejectors that utilize the kinetic energy of a jet of compressed air is widely used. The selection of the required ejector model, as well as their number (when creating a field of ejectors), is performed proceeding from the compliance of the ejector characteristics with the key parameters of the designed process technology. One of the most important characteristics of an ejector, significantly affecting the overall performance of the vacuum system, is the evacuation time of the graduated (calibrated) container. However, in technical literature, this parameter is not specified for the maximum vacuum depth produced by the ejector, nor for the corresponding supply pressure, but for certain, less-defined parameters, referred to as optimal by ejector manufacturers. In such cases, it is impossible to accurately estimate the actual value of an important criterion. Therefore, the objective of this work is to experimentally determine the actual value of the vacuum time of a graduated (calibrated) vessel for various types of ejectors.

Materials and Methods. Experimental studies were performed on a stand specifically designed and manufactured by the authors, which made it possible to study various parameters of vacuum ejectors. In particular, the stand provided establishing the exact time of vacuuming a measuring vessel using ejectors with a nozzle diameter from 0.1 to 4.0 mm at a supply pressure value that induced the maximum vacuum depth for each model under study. The research was carried out using the most popular vacuum ejectors of the VEB, VEBL, VED and VEDL families manufactured by Camozzi at a pre-determined, precisely set input supply pressure for each ejector size. The actual values of the vacuum time at the highest vacuum depth for each ejector were experimentally determined.

Results. It has been established that the performance of VEB, VEBL, VEDL, and VED series ejectors differs from that stated in the manufacturer's catalog. The time required to reach maximum vacuum for each ejector exceeds the manufacturer's specifications by 25–40%, which impacts the performance of the vacuum system.

Discussion. The experimental data have shown that the actual values of the vacuum time of the measuring vessel differ from the values given in the catalogs of manufacturers of ejectors. This difference is explained by the fact that when conducting appropriate tests, manufacturers are guided not by the maximum vacuum depth created by the ejector, but by the vacuum depth created by a certain “optimal” (the wording of the ejector manufacturer) value of the supply pressure. In almost all the cases considered by us, this “optimal” supply pressure produced a vacuum, whose depth differed from the maximum. In this regard, it seems advisable to adjust the value of the inlet supply pressure to attain the maximum vacuum depth for each type of ejector.

Conclusions. The results of the obtained values of the vacuum creation time in one liter of volume at the maximum depth of the vacuum produced by the ejector provide a more accurate selection of vacuum ejectors depending on the required process tasks, ensure the greatest efficiency and cost-effectiveness of automated vacuum systems. The research results can be used by all ejector manufacturers to adjust their basic catalogs and appropriate recommendations for the use of these products. Further research will be conducted to study the accuracy of the geometric shapes of the surface of the ejector channel, the purity of processing, and their production technology, which affect the passage of air flow.

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