Investigation of the seizing mechanism of aviation hydraulic drive spool–and–sleeves

The paper is devoted to the study of the process of seizure of spool-and-sleeve pairs of aviation hydraulic drives under the influence of contamination particles contained in working fluids of aircraft hydraulic systems. The mechanism of the particles’ action on the hydraulic drive is discussed. The process of seizure development is analysed in detail. Two techniques based on the analysis of the results are proposed that make it possible to estimate the state of the spool-and-sleeve. The first one is based on direct measurement of the gap in the spool-and-sleeve of the hydraulic drive during repair. To implement the technique it is necessary to analytically determine the minimal allowed size of the gap that would provide stable functioning of the unit over the whole pressure range of the hydraulic system. The second technique is less labour-intensive (but also less precise) in comparison to the first one and is based on the measurement of the hydraulic drive macroparameter the variation of which depends on the change of the gap size in the spool-and-sleeve during maintenance. It is necessary to determine the dependence of the macroparameter chosen on the size of the spool-and-sleeve  gap. Implementation of the described techniques will improve economic efficiency of aircraft usage by reducing the costs and the idle time in repair.