Terrain King KB21 - Hydraulic System Operation

KB21 Service Manual Pub 09-14
113
Reference
90-D. HYDRAULIC SYSTEM OPERATION
The operation of the hydraulic motor is essentially the same as the operation of the pump with the ex-
ception that the outlet oil from the pump provides oil under pressure to counter rotate the gears of the
tank and is pressurized only to the extent of the restriction in the return line.
Common Complaints
For the most part, gear pumps and motors fail as a result of, CONTAMINATION, CAVITATION (OR
LACK OF LUBE), OR OVER PRESSURIZATION.
Contamination damage results from the introduction of foreign material into the hydraulic system. The
undetectable to the human eye.
Damage due to contaminants usually takes the form of machined grooves in the thrust plates or damage
to the gears.
All Terrain King hydraulic machines are protected from some forms of contamination by a suction screen
Protect the system from potential contamination during repairs by plugging all ports which are opened
during disassembly. Rebuild the components in a dust free environment.
CAVITATION is the development and explosion of air bubbles in the hydraulic system at the pump or
of performance. This type of damage is usually the result of the loss of oil in the tank, or air leaks in the
suction line to the pump.
It is also possible to cavitate the motor during shut down by completely stopping the tractor motor and
front pump while the motor is still turning due to the momentum of the blade bar. The tractor should re-
main at the rated RPM until the blades come to a stop.
Over pressurization is the result of excessive restriction in the return line, or excessive load on the sys-
tem. All Terrain King hydraulic systems are protected from damage due to over pressurization with the
use of pressure relief valves.
Over-pressurization usually results in excessive back pressure wear to the pump housing and causes
extreme loss of performance. Extreme cases can cause torsional shear of the pump or motor shaft or
cracking of the pump or motor housing.
In addition to these modes of failure, loss of mower performance may be attributed to the failure of the
-
pler splines. This type of damage is almost always attributed to momentary or permanent misalignment
of the front pump drive assembly.