SkyTrak 3606 Service Manual - Manual (Page 202)

Section 9
9-8
9.4 HYDRAULIC FLUID
General information and specifications pertaining to
hydraulic fluid are found in Section 2 General Informa-
tion, Specifications and Maintenance Instructions.
Use only clean, filtered fluid in the hydraulic system.
After servicing or replacing a hydraulic system compo-
nent, cycle all vehicle functions several times to remove
(purge or “bleed”) air from the hydraulic system. DO NOT
build maximum pressure at the end of stroke by continu-
ing to hold the joystick function.
Inspect the hydraulic system and fluid frequently, and be
vigilant for problems or conditions including the following:
• Aeration
Aeration is the presence of air bubbles in hydraulic fluid.
Sudden, violent inward collapse of the air (known as
implosion) can occur when compressed air bubbles are
subjected to system pressure. Aeration can thus lead to
damage and overheating of components.
Pump aeration will produce a loud crackling sound, as
though rocks or marbles were being forced through the
pump. Excessive aeration will give the hydraulic fluid a
cloudy or milky appearance, and cause erratic operation
of hydraulic system components.
Aeration is caused by air being introduced into the sys-
tem, possibly through a leaky seal or joint in the pump or
elsewhere in the system. Check for leaky hydraulic cylin-
ders and threaded fittings; introduction of a special dye,
visible under fluorescent light, may be helpful in deter-
mining the source of the leak.
• Cavitation
Cavitation occurs when hydraulic fluid fails to entirely fill
an existing space. Cavitation, like aeration, can produce
a loud crackling sound, as though rocks or marbles were
being forced through the system. Cavitation can be due
to a low hydraulic oil level in the reservoir, a restricted
intake line, or improperly high fluid viscosity.
• Contamination
Contamination, or dirt, can be any material other than
hydraulic fluid that causes harm or decreases the perfor-
mance of the system. Contaminants include solids, liq-
uids, and gasses. Most contaminants are abrasive in
nature, causing rapid wear or damage to the system.
• Excessive heat
Excessive heat is a relative thermal condition that effects
fluid viscosity. Extreme operating conditions, such as
excessive operation, outside air temperature, and factors
including aeration, cavitation, contamination and over-
pressurization can cause fluid and component tempera-
tures to go beyond their specified limits. Excessive heat
causes oxidation in hydraulic fluid to occur more rapidly,
breaking down its viscosity. A chain reaction then results,
and can lead to component damage or failure. The true
cause of an excessive heat condition must be diagnosed
and cured, or the problem will recur.
• Implosion
An implosion is a sudden, violent inward collapse, and
can often cause a vacuum effect. Imploding air bubbles
within a hydraulic system can cause component damage.
• Over-pressurization
Over-pressurization is, simply, pressure greater than that
for which a component was engineered to withstand or
operate under. Over-pressurization can cause equipment
damage. DO NOT attempt to adjust or tamper with pres-
sure cartridges, settings, etc., unless otherwise specified.
• Viscosity
Viscosity is the property of a fluid or semi-fluid that
enables it to develop and maintain shearing stress
dependent upon flow rate (velocity), and to offer contin-
ued resistance to flow. In other words, viscosity is a mea-
surement of a fluid's resistance to flow (internal friction).
Model 3606 • Origin 10/99