Viscosity is the single most important property of the hydraulic oil. The viscosity is a measure of
hydraulic oil’s resistance to gradual deformation by shear stress or tensile stress. According to ISO
Viscosity Classification scale, the proposed ISO VG32 oil must have kinematic viscosity at 40 °C
between 29.8 and 35.2 mm2
/s (cSt) [2]. In all three elevators, the kinematic viscosity of the working
hydraulic oil is above the upper limit. This means that working oils comply with the specification.