Specifications; Hydraulic Fluid - JLG sky trak mmv Service Manual

9.3

SPECIFICATIONS

Refer to Section 2.5, Specifications for hydraulic system
specifications.
9.4

HYDRAULIC FLUID

General information and specifications pertaining to hy-
draulic fluid are found in Section 2.5.9, Hydraulic System .
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
look 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 im-
plosion) 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 by introducing a special dye,
visible under fluorescent light, which may be helpful in de-
termining 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 in-
take line, or improperly high fluid viscosity.
Model MMV Rev. 12/04
Contamination
Contamination, or dirt, can be any material other than hy-
draulic fluid that causes harm or decreases the perfor-
mance of the system. Contaminants include solids,
liquids and gases. Most contaminants are abrasive in na-
ture, 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 ex-
cessive operation, outside air temperature and other fac-
tors including aeration, cavitation, contamination and
over-pressurization can cause fluid and component tem-
peratures to go beyond their specified limits. Excessive
heat causes oxidation in hydraulic fluid to occur more rap-
idly, breaking down its viscosity. A chain reaction then re-
sults and can lead to component damage or failure. The
true cause of an excessive heat condition must be diag-
nosed 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 pressure greater than that for
which a component was engineered to withstand or oper-
ate 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 en-
ables it to develop and maintain shearing stress depen-
dent upon flow rate (velocity), and to offer continued
resistance to flow. In other words, viscosity is a measure-
ment of fluid resistance to flow (internal friction).
Hydraulic System
9.5