Cargo pumps represent a critical hydraulic application.
Info Centre >> Fuel and Lube Oil Technical Manual >> 7. Lube Oil - Test Results >> 7.6 Hydraulic Oil >> 7.6.1 Viscosity
Hydraulic Oil Viscosity
A sudden rise or fall in the measured viscosity of a hydraulic oil is usually the result of a wrong grade of oil being added to the system.
This type of problem may require urgent remedial action if the result is that the fluid ends up being thinner or thicker than limits allow. Oils that are too thin may not provide effective lubrication and oils that are too thick may give rise to excessive pressure, particularly at start up in cold weather.
The usual indication of oxidation processes in oil is a slow rise in TAN and viscosity. Viscosity rise is however only a reliable indicator of this condition for monograde oils. The high viscosity index of multigrade oils is normally achieved by use of polymeric additives and most of these additives show some tendency to shear down over time. This tendency will give rise to a reduction in the viscosity of the oil.
There are potentially three reasons for viscosity change in a hydraulic fluid: