ENGINEMAN 1 & C
pins or keys; or breakage of gearing, shafting, or
linkage. Elimination of troubles resulting from
any of these causes should be accomplished ac-
cording 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 lubrica-
tion, and the maintenance of all the units and the
fluid in the required state of cleanliness. Regular
operation of hydraulic equipment prevents the
accumulation of sludge and the freezing of adja-
cent parts, and aids in preventing corrosion. The
necessity of proper lubrication and cleanliness
cannot be too strongly emphasized.
Detailed instructions on the maintenance of
a specific unit should be obtained from the
appropriate manufacturers technical manual, but
the following general information will also be
The Fluid System
If an inspection of an oil sample drawn from
a hydraulic system reveals evidence of water,
sludge, or acidity, the system must be
DRAINED, then CLEANED with the prescribed
acid-free cleaning fluid (flushing oil), and
FILLED with clean hydraulic oil. A hydraulic
system may be drained and cleaned as follows:
1. Remove permanent filters and wash them
in flushing oil. Then use low pressure air for dry-
ing purposes. If filters have replaceable elements,
install new elements.
2. Drain the system of old hydraulic oil as
completely as possible.
3. Close all connections and fill the system
with acid-free cleaning fluid.
4. Start and operate the unit under idling con-
ditions in order to fill the system thoroughly with
the cleaning fluid.
5. Secure the unit and allow it to stand idle
for the prescribed period (usually about an hour).
This period of idleness permits the cleaning fluid
to dissolve any sludge.
6. Start and operate the unit with a light load
for a short interval of time (3 to 5 minutes, unless
otherwise specified). Allow the equipment to stand
idle for about 15 minutes, then repeat the whole
cleaning process. Do this two or three times.
Never operate a hydraulic unit with a full load
when it is filled with cleaning fluid. Keep the
operating pressure as low as possible.
After each short operating period, turn the
cleaning handles of edge type filters (if installed)
and drain from the filter an amount of cleaning
fluid equal to its volume.
7. If time permits, allow the system to stand
idle for an additional hour following the series
of short operating periods.
8. Drain the system of cleaning fluid. Reclean
permanent filters, if necessary; install new
replaceable filters. Close the system, and fill it
with the proper hydraulic oil.
As the system is filled, the hydraulic oil should
be strained through a fine wire screen of 180 or
200 mesh. If oil is not clean, it should be run
through a centrifuge. Adequate protection should
be provided against dust and moisture. Moisture
should be expelled from the oil before it is poured
into a system; oil with noticeable water content
should be rejected or centrifuged.
When a hydraulic system is being filled, suf-
ficient hydraulic fluid should be used to com-
pletely fill the active parts of the mechanism,
leaving no air pockets. Air valves should be
opened during the filling process, so that air can
escape to the oil expansion box. Be sure the valves
are closed tightly after the system has been filled.
Pumps and Motors
Whether the pumps and motors of hydraulic
transmissions are of the axial or radial piston type,
the maintenance procedures, as well as the
operating principles, are relatively the same. In
general, maintenance information on other types
of pumps also applies to hydraulic pumps and
Neoprene is utilized as a seal around the shafts
of most modern hydraulic pumps and motors, but
other types of shaft packing are also used.