Service Manual

HGM-H 9
SERVICE AND MAINTENANCE
PURGING PROCEDURE
The HGM-H motor can not be purged of air
as a stand alone component. The hydraulic
system as a whole will need to be purged after
any addition of oil to the system or a complete
oil change. This will most likely involve the use
of the hydraulic pumps bypass feature. If this
is not available, see the manufacturers recom-
mendation for air purging.
Due to the effects air has on efciency in hy-
drostatic drive applications, it is critical that air
is removed or purged from the system.
These purge procedures must be preformed
anytime a hydrostatic system has been opened
for maintenance or repair, or if any additional
oil has been added to the system.
Air creates inefciency because it has compres-
sion and expansion rates that are higher than
that of oil.
Air trapped in the oil may cause the following
symptoms:
1. Noisy operation.
2. Lack of power or drive after short-term
operation.
3. High operation temperature and excessive
expansion of oil.
Before starting, make sure the reservoir is at
the proper oil level. If it is not, ll to the vehicle
manufacturer’s specications.
The following procedures should be performed
with the vehicle drive wheels off the ground,
then repeated under normal operating condi-
tions.
WARNING
POTENTIAL FOR SERIOUS INJURY
Certain procedures require the vehicle
engine to be operated and the vehicle to
be raised off of the ground. To prevent
possible injury to the servicing techni-
cian and/or bystanders, insure the ve-
hicle is properly secured.
1. With the vehicles pump assembly bypass
valve open and the engine running, slowly
move the directional control in both forward
and reverse directions (10 to 20 times). As
air is purged from the unit, the oil level in
the reservoir may drop.
2. With the bypass valve closed and the engine
running, slowly move the directional control
in both forward and reverse directions (10
to 20 times). Check the oil level, and add
oil as required after stopping engine.
3. It may be necessary to repeat steps 1 and 2
until all the air is completely purged from the
system. When the hydraulic system moves
forward and reverse at normal speed and
the reservoir oil remains at a constant level,
purging is complete.