In any hydraulic equipment, clean, dry oil can extend
equipment life more than the normal operating life. British hydraulics
research has shown that solids contaminated particles when removed from
oil can increase machine life to a great extent. There is great benefit
in having clean oil. It increases the machine's life and maintenance gap
up to ten times. Many hydraulic equipment manufacturers have agreed to
the fact that oil cleanliness has a major effect on wear within their
equipment. Some of them are now specifying how clean must be the oil
used in their hydraulic equipment if warranty claims are to be honored.
How do you grade oil cleanliness ? Solid particle counts in oil can be
done with optical equipment using an electron-scanning microscope or by
sifting through screens. Each procedure produces different particle
counts because of their varying sensitivity in detecting particles of
different sizes. The ESM detects many more of the smaller particles than
the optical methods. Counting standard ISO 4406 -1999 is used globally
to rate solids contamination of oils.
Three scale-numbers are used to describe solids contamination where
calibrated automatic counting devices are used to measure contamination.
These are the 14 micron and larger, 6 micron and larger, 4 micron and
larger. When the count is done by optical microscope two size ranges are
used the 15 micron and larger and 5 micron and larger.
How contaminated oil destroys hydraulic equipments? Dirty oil implies
rapid destruction for hydraulic machinery and lubricated equipment. Fine
tolerance hydraulic machines can have clearances between parts of 5 to
10 microns . Solid particles larger than the clearance gap will jam or
block the space. In equipment with larger tolerances the oil film
between parts can get as thin as 3 to 5 micron. Solids in oil are like
grinding paste. They block oil passages and makes the oil more viscous.
The longer the oil is left dirty the faster the rate of failure. The
only solution is to keep the oil clean by filtration.
Measuring Oil Contamination
Oil samples can be taken and analyzed in a laboratory which include
tests that quantify:
- The number and size of particles.
- The types of contaminants present.
- The quantity of contaminants.
- The condition of the additives in the oil.
- The amount of water present.
- The oil’s viscosity.
