The subject of study in the article is the amount of leaks of the working fluid in the gap between the plunger and the bushing of an aircraft axial-plunger pump, depending on the position of the plunger relative to the bushing. The level of fluid leaks in the gap between the plunger and the cylinder block bushing is a component of volumetric losses, affects the thermal state, wear, the state of the plunger-bushing pair, as well as the level of pressure pulsations of the working fluid and, ultimately, the change in the efficiency of the axial-plunger pump. Researches deal with the influence of piston defects in a bushing on losses through a gap between them that is not discovered in existent literature. The aim of this work is theoretical research of the influence of piston defect on the leakage of working liquid through a gap between the piston and cylindrical bushing in aviation axial-piston pump under workloads. The tasks are: it is necessary to define the losses quantity for the three cases: the axes of piston and bushing coincide; piston is displaced (axes are parallel) with a maximal eccentricity ε = 0.99; piston is twisted in a bushing so that the edges of piston touch a bushing. For the problem-solving methods as follows were used. The task of thin film laminar flow in a gap between piston and bushing was solved by a numeral method in finite-element software. Losses on a piston are considered as a sum of the losses, related to the motion of the piston at a speed W and losses due to the pressure gradient dp/dz. The results are: to obtain the laws of geometrical parameters influence on the losses amount investigation for one piston was undertaken in the first part of the study. It is marked that most losses take place for piston displaced in parallel, and the least - for twisted. Total losses for the real pump on different operational behaviors are considered and volume loss-of-flows are obtained in the second part of the article. Conclusions. Dependences of losses through a gap at the different gap sizes and relative length of bushing for twisted piston are first time obtained. The results allow estimating the losses quantity in a pump on the efficiency of his work at planning and exploitation.

In this article, the task is to consider the effect of the piston bending in an axial- piston pump under the action of hydraulic force on the kinematics of the pump. The change in kinematics due to the elastic deformation of the piston is estimated by the axial displacement of the piston face. The study takes into account the bias of the plunger in the gap, the elastic bending deformation of the plunger, the contact deformation of the plunger and the cylinder block. The task is considered on three models: a rigid piston in a rigid cylinder block; deformable piston in a rigid cylinder block; deformable piston, block, shoe, and disk. The values of the displacement of the piston, caused by elastic forces and misalignment in the gap depending on its position were obtained for the first time as a result of the analysis. The problem is solved both analytically and numerically using the finite element method. In the analytical solution of the problem, the piston is represented as a beam supported by pin and roller at the points of contact of the piston with the walls of the cylinder block. The three-dimensional model of the pump is applied to solve the problem by the finite element method, the contact deformation of the piston and the block is considered. According to the simulation results, the displacement of the piston is obtained depending on the position of the piston. The results of modeling an analytical model are presented in the form of a smooth function, and the results of numerical simulation using the finite-element method obtained for several points are interpolated by a smooth function. The conclusions suggest that the greatest deformations are achieved in the piston located at the bottom dead center, and the gap between the piston and the sleeve and the overall stiffness of the contact parts have the greatest effect. The results of the work can be used to correct the geometrical parameters of a heavily loaded aviation axial-plunger pump to reduce flow and pressure pulsations caused by the kinematics of the pump.