Case study
An inspection of two axial piston motors
that had failed well short of their expected service life revealed that the
motors had failed through inadequate lubrication, as a result of low fluid
viscosity caused by excessive fluid temperature.
How does this happen?
As the temperature of petroleum-based
hydraulic fluid increases, its viscosity decreases. If fluid temperature
increases to the point where viscosity falls below the level required to maintain
a lubricating film between the internal parts of the component, damage will
result.
The temperature at which this occurs
depends on the viscosity grade of the fluid in the system. Hydraulic fluid
temperatures above 82°C damage seals and reduce the service life of the fluid.
But depending on the grade of fluid, viscosity can fall to critical levels well
below this temperature.
How can this type of failure be
prevented?
The above example highlights the
importance of not allowing fluid temperature to exceed the point at which
viscosity falls below the optimum level for the system's components.
Continuing to operate a hydraulic system
when the fluid is over-temperature is similar to operating an
internal-combustion engine with high coolant temperature. Damage is pretty much
guaranteed.
Therefore, whenever a hydraulic system
starts to overheat, shut down the system, find the cause of the problem and fix
it!
Warm up the cold hydraulic fluid to a
temperature with in operating range in cold climate before putting the
hydraulic machinery on load.
