Page 67 - Fluid Power Engineering

44 Cha pte r T w o

• Leakage from oil-water heat exchangers.
• Filling of moisture-contaminated hydraulic fluid from badly
stored containers.

Several harmful effects from moisture contamination may occur,
including:

• The formation of rust and subsequent mechanical problems.
• The destructive effect of surface wear. Rust particles can
promote the formation of oxidation sludge and deposits that
may cause serious malfunctions in system parts.
• Rust particles circulating with the hydraulic fluid may cause
abrasive wear.
• Formation or accumulation of rust against dynamic seals
results in accelerated wear of the seals and increasing leakage
of the hydraulic fluid.
• The free and dissolved water reduce the fatigue strength of
ball bearings and stressed alloy steel components.

The following are possible ways to minimize the moisture content:
• Regular draining of undissolved water and sludge from a
drain cock fitted at the lowest point of the fluid reservoir.
Therefore, a good design of the reservoir and its floor slopes
is important.
• The hydraulic fluid should have good demulsibility which is
the ability of a hydraulic fluid to separate from water. The
best demulsibility is achieved by the most highly refined
mineral-based oils and certain synthetic oils.
• Using filter elements capable of removing limited amounts
of free water from hydraulic fluids. This is not, however, an
economic solution for systems subject to continuous contam-
ination by signifi cant quantities of water.

Solvent Contamination
Solvent contamination is a special form of foreign fluid contamina-
tion in which the original contaminating substance is a chlorinated
solvent. When the chlorinated solvents are allowed to combine with
minute amounts of water, they change chemically into hydrochloric
acids. These acids attack the internal metallic surfaces in the system
and produce severe rust-like corrosion.
Foreign-Fluids Contamination
Hydraulic systems can be contaminated by foreign fluids other than
water and chlorinated solvents. This type of contamination is gener-
ally a result of lubricating oil, engine fuel, or incorrect hydraulic fluid