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UNDERSTANDING HYDRAULICS
TESTING HYDRAULIC FLUID
Test the uid regularly. A number of formal test kits are available to evaluate the condition
of hydraulic uid or a uid sample can be sent to a lab for evaluation. However, there are
simple signs of uid 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 sched-
ule. One of the most important elements in such a program is changing or adding to the
uid on schedule.
WHEN TO CHANGE FLUID
Blotter spot test. This is a very simple test in which a drop of uid 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 uid 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 uid 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 uid's condition.
Test for acid content. A shift in the acid content may indicate a break down in the uid.
Acid test kits are available from uid suppliers and the tests are easy to carry out.
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