containing the various operating mechanisms and their
units, such as brakes, steering, lift cylinders, extend
cylinders, and hydraulic motors.
Since an actuating mechanism is dependent on the
power system, some of the troubles exhibited by the
actuating system may be caused by difficulties in the
power system. By the same token, a trouble symptom
indicated by a unit of the power system may be caused
by leakage from one of the units of an actuating system.
When any part of the hydraulic system becomes
inoperative, refer to the schematic diagrams located in
the applicable technical manual (in conjunction with
tests performed on the equipment) to assist in tracing the
malfunction to its source. As previously stressed, NO
UNIT SHOULD BE REMOVED AND REPLACED
(OR ADJUSTED) UNLESS THERE IS SOUND
REASON TO BELIEVE IT IS FAULTY.
Most hydraulic troubles can be included in one or
more of the following categories: lack of fluid supply,
external leaks, internal leaks, physically defective units,
or related troubles caused by mechanical control
linkages and electrical control circuits.
Insufficient fluid in the system results in no pump
delivery or at best a sluggish or erratic operation. The
reservoir must always contain sufficient fluid to till the
system completely without letting the pump run dry. The
proper fluid must always be used to replenish a low
system. Do not mix hydraulic fluids or reuse old fluid.
Make sure all replenishment fluid is properly filtered
before it is dispensed into the reservoir. Remove and
repair or replace defective units when there is an
indication of external leakage of the unit.
If foreign particles are found when you remove and
disassemble a unit, identify and trace them to the source;
for example, a common source of foreign particles is
found in flexible hose. Generally, the cause is improper
installation or internal deterioration; either can release
slivers of the lining into the system, causing units to leak
or become inoperative.
To analyze malfunctions in hydraulic systems, like
all other systems, you need to have a complete under-
standing of the system and its operating components.
Also, you need to know the interrelationship of one
component to another; for instance, a complete under-
standing of a pressure regulator lends itself to trouble-
shooting the entire system as well as the regulator itself.
Pressure regulators, like all hydraulic components,
are normally reliable pieces of equipment; nevertheless,
the y can malfunction. Keep in mind, though, that instead
of being a source of trouble, the regulator can be a fairly
reliable watchdog on the other units in the system. The
particular behavior of the regulator may be the only
indication of leakage in places where no other indication
is available. It should be kept in mind that trouble-
shooting the regulator is done only after the obvious
steps have been taken, such as checking the system fluid
level to check for external fluid loss and opening shutoff
Troubleshooting the pressure regulator is done by
timing the cycle of operation-from the cut-in position
to the cutout and back to the cut-in position. A standard
regulator operating in a normal system completes this
cycle in a certain period of time. This time can be
obtained from the equipment manual or closely
estimated by maintenance personnel.
Since you normally use the pressure regulator only
with a constant volume pump, it should take a certain
definite time to buildup system pressure; for example,
suppose a pump has a volume output of 6 gallons per
minute, and the system requires 1 gallon of fluid to
become completely tilled (pressurized). As the system
takes only one sixth of the pump output to build up
pressure, it should require only one sixth of a minute
(10 seconds) to pressurize the system. This is true if the
system is in good operating condition. But what if the
system contains an internal leak? In the 10 seconds
usually required to build up pressure, the pump is still
delivering 1 gallon, but some of the fluid is being lost.
Thus, at the end of 10 seconds, the system cannot be
pressurized; therefore, the regulator cannot be cutout.
The cut-in and cutout pressure of the regulator can be
seen on the system pressure gauge. Once the regulator
is cut out, the system should hold fluid under pressure
for a reasonable length of time; however, if the system
leaks, pressure drops fast and the regulator cuts in faster
than normal. These indications may mean that the
regulator is faulty or the other components in the system
are faulty; however, by isolation techniques, such as
subsystem operation, and checking shutoff valves, the
problem can be located.
If the fault is the regulator, it is probably leaking at
the regulator check valve or at the regulator bypass
A leaking regulator check valve is one of the most
common and easily recognized troubles. Again the
regulator cycle is affected. With the regulator cut-in, the
check valve is open, and fluid is flowing into the system.