The changes of viscosity parameters for Elevator I are depicted in Figure 1. It is obvious that
working oil’s kinematic viscosity at 40 °C was outside the specification limits in all samples. It is
noted that for the sample taken in May 2013 there is an increase of the value, meaning that the elevator
is not operating well. This is one of the basic reasons to change the hydraulic oil in the elevator’s
hydraulic machine.