Energy Loss Coefficients ki in a Displacement Pump and Hydraulic Motor used in Hydrostatic Drives

The article aims at defining and analysing the energy loss coefficients in design solutions of rotating displacement machines, with a piston machine as an example. The energy losses observed in these machines include mechanical loss, volumetric loss, and pressure loss. The scale and relations between these losses in different machines depend on machine design and manufacturing quality, and on operating parameters. The operating parameters, in turn, which affect directly or indirectly the above losses depend on whether the machine works in pump or hydraulic motor regime. The article is also a contribution to the development of a library of k_i coefficients which define the losses in displacement machines, as the knowledge about these coefficients makes it possible to assess fast and easily the energy efficiency of a machine or drive system at each point of its working area.