conditions that lead to additional trouble, since dirt may
enter an open system.
Leaks are a frequent cause of trouble in hydraulic
equipment. Generally, leaks are a result of excessively
worn parts, abnormal and continuous vibration,
excessively high operating pressures, or faulty or
careless assembly. External leaks usually have little
effect on the operation of equipment other than a steady
draining of the oil supply. Even a small leak wastes oil,
and the resulting unsightly appearance of a machine is
indicative of poor maintenance procedures.
External leaks may result from improperly
tightened threaded fittings; crossed threads in fittings;
improperly fitted or damaged gaskets; distorted or
scored sealing rings, oil seals, or packing rings; scored
surfaces of working parts; improperly flared tube ends;
or flanged joints not seating squarely.
Internal leaks usually result in unsatisfactory
operation of the equipment. Large internal leaks are
signified by a loss of pressure and the failure of
equipment. While large internal leaks can usually be
located by installing pressure gauges in various parts of
the equipment, the location of small leaks generally
requires disassembly and visual inspection of the parts.
Internal leaks may result from worn or scored valves,
pistons, valve plates or bushings, or improperly fitted or
The most common symptom of trouble in a
hydraulic system is an unusual noise. Some noises are
characteristics of normal operation and can be
disregarded, while others are evidence of serious
trouble. Even though the exact sound indicating a
specific trouble can be learned only through practical
experience, the following descriptive terms will give a
general idea of which noises are trouble warnings.
If popping and sputtering noises occur, air is
entering the pump intake line. Air entering the system at
this point may be the result of too small an intake pipe,
an air leak in the suction line, a low oil level in the supply
tank, cold or heavy oil, or possibly the use of improper
If air becomes trapped in a hydraulic system,
hammering will occur in the equipment or transmission
lines. When this occurs, check for improper venting.
Sometimes, a pounding or rattling noise occurs as the
result of a partial vacuum produced in the active fluid
during high-speed operation or when a heavy load is
applied. This noise may be unavoidable under the
conditions stated and can be ignored if it stops when
speed or load is reduced. If the noise persists at low
speeds or light loads, the system needs to be vented of
air. Air in a hydraulic system can also cause uneven
motion of the hydraulic motors.
When a grinding noise occurs, it can usually be
traced to dry bearings, foreign matter in the oil, worn or
scored parts, or overtightness of some adjustments.
The term hydraulic chatter is sometimes used to
identify noises caused by a vibrating spring-actuated
valve, by long pipes improperly secured, by air in lines,
or by binding of some part of the equipment.
Squeals or squeaks indicate that the packing is too
tight around some moving part or that a high-frequency
vibration is occurring in a relief valve.
Even though troubles occurring in electrical
equipment are the responsibility of the Electricians
Mate, the Engineman can help maintain the equipment
by making a few simple checks when electrical troubles
occur. Failure to have a switch in the ON position will
cause unnecessary delay in operating electrical
equipment. If the switch is closed and the equipment still
fails to operate, check for blown fuses or tripped circuit
breakers. Troubles of this type are usually the result of
an overload on the equipment. If a circuit breaker
continues to cut out, the trouble may be caused by
damaged equipment, excessive binding in the hydraulic
transmission lines, or faulty operation of the circuit
breaker. Check for visual indication of open or shorted
leads, faulty switches, or loose connections. Do not
make repairs to the electrical equipment or system. Do
not open enclosures of electrical equipment, but do
report evidence of possible electrical failure to the
When electrohydraulically driven auxiliary
inoperative because of a
mechanical failure, a check should be made. Look for
improper adjustment or misalignment of parts; shearing
of pins or keys; or breakage of gearing, shafting, or
linkage. Elimination of these causes should be done
according to the manufacturers instructions for the
specific piece of equipment.
The principal requirements necessary to keep a
hydraulic transmission in satisfactory operating
condition are regular operation, proper lubrication, and