When a hydraulic system is worked on, cleanliness is
No. 1. Dirt and metal particles can score valves, seize
pumps, clog orifices, resulting in major repair work.
Oil and Filter Changes
Despite all the precautions you take when working
on the hydraulic system, some contaminates will get into
the system anyway. Good hydraulic oils will hold
contaminates in suspension and the filters will collect
them as oil passes through. A good hydraulic oil contains
additives that work to keep contaminants from damaging
or plugging the system. However, these additives lose
their effectiveness after an extended period of time;
therefore, oil changes at the recommended intervals can
ensure that contamination is held to a minimum. By
changing the oil at its recommended interval ensures that
the additives will do their job.
Regular filter changes ensure solid particles are
removed from the system. They should be changed
more often under adverse operating conditions. When
filters are changed, thoroughly clean the filter housing
before installing a new filter. Remember to add enough
fluid to compensate for any fluid lost in filter
Cleaning and Flushing the System
Cleaning and flushing the system should be
performed based on the manufacturers recommendation
or when the system is known to be contaminated. The
nature and amount of deposits in a particular system may
vary widely. Inspection of the system may show any
condition between a sticky, oily film and a hard, solid
deposit (gum or lacquer formation) which completely
chokes off the system. If the system is drained
periodically according to the manufacturers recom-
mendations, the formation of gum and lacquer will be
If there is no gum or lacquer formation suspected,
clean the system as follows:
1. Drain the system completely.
2. After draining, clean any sediment from the
reservoir, and replace the filter elements.
If flushing is required because the oil is badly
contaminated, clean and flush the system as follows:
1. Drain the system completely.
2. Refill the system with the recommended hydraulic
oil for the system involved.
3. Operate the equipment to cycle the flushing oil
through the system. Ensure that all valves are
operated so that the new oil goes through the lines.
The time necessary to clean the system
will vary, depending on the condition of the
equipment. Usually from 4 to 48 hours is
sufficient for most systems.
(Drain out the flushing oil, replace the filters, and
refill the system with clean hydraulic oil of the
If gums or lacquer has formed on working parts and
the parts are sticking, remove the affected parts and clean
them thoroughly. Consult the manufacturers manual
before removing and cleaning any parts for proper
Leaking hydraulic connections are frequent reasons
for maintenance. Some leaks are external, being evident
on the outside of components. Others are internal, which
does not result in actual loss of oil, but it does reduce the
efficiency of the system.
INTERNAL LEAKAGE.A small amount of
internal leakage is allowed to provide lubrication of
moving parts. This leakage is normal and does not result
in faulty operation. On the other hand, an excess of
internal leakage results in slow operation, loss of power,
and overheating of the hydraulic fluid. The cylinders may
creep or drift and, if the leak is bad enough, the control
valves may not function properly.
Internal leaks are caused by wear of the seals and
mating parts during normal operation. Leakage is
accelerated by using oil that has too low a viscosity
because the oil thins faster at higher temperatures. High
pressures also force more oil out of leaking points in the
system. This is why excessive pressures can actually
reduce the efficiency of the hydraulic system.
Internal leaks are hard to detect. Usually, all you can
do is observe the operation of the system for signs of
sluggishness, creeping, and drifting. When these signs
appear, it is time to test the system and pinpoint the
EXTERNAL LEAKAGE.External leaks not
only look bad but make it hazardous for the operators of
the equipment. A leak that allows floor plates to become
slippery may cause the operator to fall on or off the