JLG TOUCAN DUO, Руководство по обслуживанию, Страница: 31 / 108

31
TOUCAN Duo
Updated 06-2015
Models
GENERAL III-21 III-21
A pump that is either cavitating or operating on aerated
fluid is usually noisy, and the system operates in a
jerky manner.
If erosion, on the suction side of the pump is evident
of the gear track, the cause was due either to air
bubbles in the oil or starved suction.
5. Lack of oil.
When a failure is due to lack of oil, deterioration is
usually rapid. This type of failure can occur from either
or two condition :
(a) Oil level is low in the tank or
(b) There is an air leak in the suction line.
6. Excessive heat.
Excessive heat will harden O-rings and seals.
Excessive heat usually results from a relief valve set
too low. If a relief valve is set too low, part of the oil will
be dumped across the relief valve at each cycle. In this
case the machine will be very slow.
7. Oil pressure too high.
There are two reasons for overpressure :
(a) The relief valve fails to function, producing an
extreme surge and immediate failure,
(b) The relief valve setting is too high, resulting in
repeated pressure peaks.
Damage to the pump looks very similar in both
cases.
8. Incorrect assembly.
This type of failure is self explanatory ; either
components are faulty or parts were not assembled
correctly.
Pinching of the O-ring will occur if not properly placed
in its groove. If the O-ring is installed incorrectly, the
housing surface will show a depressed area (especially
if the part is made of aluminium).
2. Abrasive wear caused by metal particles.
Metal contaminants usually results from components
wear in the hydraulic system which was insufficiently
flushed after a previous failure. Metal particle damage
may be gradual or fairly sudden, depending on the
quantity and size of the particles. Metal particle
damage is indicated by surface scratches on the
pressure plates.
A pressure plate will have several circular scratches
if particles of more than 125 microns are present. If
exposed to particles of this size long enough, the
entire surface will be rough and heavily grooved.
With abrasive wear from metal particles, the shaft
bearing area will have many small grooves. The
severity of damage will depend on the amount of
contamination in the system and on operating
pressure.
A worn housing will have grooves in the gear track
caused by large particles being caught between tips
of the gear teeth and body. This usually results from
the failure of another component.
3. Incorrect installation.
Incorrect installation can create external loads on the
pump which can result in various types of failures.
4. Aeration or cavitation.
Cavitation and aeration act very much alike in the
system. This type of failure is rare, and careful
investigation is required to pinpoint it.
Aeration occurs when air mixes with the oil. Air may
enter the system through a small suction leak or by
agitation of the surface of the oil in the tank. Surface
agitation occurs when return oil is dumped back above
the surface of the oil. This can occur when the oil
level is too low.
Cavitation is the formation and collapse of vapour
bubbles in the oil. This is usually the result of
restricted pump suction. Cavitation occurs more
readily when the oil is cold.
Aeration and cavitation erode and pit the pressure
plates and pump housing.