Rotary hydraulic motors belong to hydrostatic converters
that work on volumetric principle. The geometric volume
VgM is one of their most important properties. The volume
is given by a liquid volume, which flows through an
unloaded hydraulic motor within one revolution of the
motor shaft. A suitable rotary hydraulic motor is chosen
on the basis of static characteristics. Flow, torque and
speed characteristics belong to most important
characteristics of hydraulic motors. The efficiency of
rotary hydraulic motors is a very important parameter
too. It is possible to diagnose e.g. technical conditions of
rotary motors on the basis of their efficiency. In the case
of hydraulic motors, it is necessary to determine flow,
mechanical-hydraulic and total efficiencies. The abovementioned
parameters of rotary motors are the basis for
their suitable applications [1, 2].