Toro TimeCutter SW 4200, Service Manual

Page: 70 / 142

HYDROSTATIC DRIVE SYSTEM
5-5 Toro Timecutter SW/SWX Service Manual
5
\
Purging Procedure
Due to the effects air has on efficiency in hydrostatic
drive applications, it is critical that it be purged from the
system.
This purge procedure should be implemented any time
a hydrostatic system has been opened to facilitate
maintenance, any additional oil has been added to the
system, or a replacement transaxle has been installed.
Air creates inefficiency because its compression and
expansion rate is higher than that of the oil in hydrostatic
drive systems.
The resulting symptoms in hydrostatic systems may be:
• Noisy operation
• Lack of power or drive after short term operation.
• High operation temperature and excessive
expansion of “oil”; in the latter case, oil may
overflow.
The following procedure should be performed with the
vehicle wheels off the ground and then repeated under
operating conditions.
1. With the bypass valve open (push position) and the
engine running, slowly move the directional controls
(forward/reverse levers) in both forward and reverse
directions 5 to 6 times; as air is purged from the
transaxles, the oil level will drop.
2. With the bypass valves in the closed position (run
position) and the engine running, slowly move the
directional control levers in both forward and reverse
directions 5 to 6 times.
3. It may be necessary to repeat steps 1 and 2 until
all air is completely purged from the transaxles.
When the transaxles move forward at normal speed,
purging is complete.