46 02/02
UNDERSTANDING HYDRAULICS
TESTING HYDRAULIC FLUID
Test the fluid regularly. A number of formal test kits are available to evaluate the condition of hydraulic
fluid, or a fluid sample can be sent to a lab for evaluation. However, there are simple signs of fluid
degradation such as a color shift, bad aroma, or feel of grit in a sample.
Don't neglect maintenance. Set up and adhere to a rigid preventative maintenance schedule. One of the
most important elements in such a program is changing or adding to the fluid on schedule.
WHEN TO CHANGE FLUID
Blotter spot test. This is a very simple test in which a drop of fluid is placed on a piece of blotter
paper. If the blotter remains colorless or develops only a light yellow ring, oxidation is under control.
Even when color develops but is uniform throughout, the oil is serviceable. If the sample shows distinct
rings, the fluid should be changed. When a distinct dark spot remains in the middle but lighter-colored
oil migrates outward in the blotter paper, the oil has or is about to dump sludge or other products into
the system. This indicates that the time for fluid replacement has passed.
Listen for a sound change. If the operating system changes in sound level usually louder or other
than normal sounds, it is time to evaluate the fluid's condition.
Test for acid content. A shift in the acid content may indicate a break down in the fluid. Acid test
kits are available from fluid suppliers, and the tests are easy to carry out.
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