Hydraulic System Modification; Hydraulic Pump: Kx121-3S , 161-3S , U45-3; Control Valve: Kx121-3S , 161-3S , U45-3; Travel Motor: Kx121-3S , 161-3S , U45-3 - Kubota KX91-3a Workshop Manual

WSM Minor Change
C. Hydraulic system modification
a. Outline
In order to improve further "Load Sensing Performance", pump and control valve have been changed
in several parts. Main parts of minor change are as follows.

1. Hydraulic pump: KX121-3S , 161-3S , U45-3

(1) Valve plate opening performance improved
End milling finish to V-shape notch
(2) Piston shoe type change
Multi-pad type to single-pad type
(3) Cylinder block center spring foree upgraded
(4) Swash plate shape change
(5) Swash plate pin shape change
(6) PC regulate spool pin dia. 3.5
Horse power spring change
(7) LS valve compact size
PC orifice 0.6 added

2. Control valve: KX121-3S , 161-3S , U45-3

(1) Damper chamber added in the unload valve (orifice 1.2)
(2) In order to achieve the stable response of PLS signal line;
1.0 orifice added in valve's PLS port plug.
Hose volume (1/4"
(3) Shuttle plate change;
Outer dia is approx. 20 m larger in minor change
(4) Compensation spools of arm, bucket and swivel;
orifice machining deleted.

3. Travel motor: KX121-3S , 161-3S , U45-3

(1) Moter swash plate:
(2) Hi-Low piston:
(3) Thrust plate:
(4) Sun gear:
(5) Ring nut:
(6) Reduction gear case drain port size: G 1/4, hex. 6
4. Role of hose volume (1/4" 350mm)
The hose volume control that is attached on the control valve serves as a sort of damper. At a start
of operation in particular (to start traveling, for example), it is effective in avoiding a sudden surge
pressure and preventing the machine from starting with a jerk. In other words, violent fluctuations
of load pressure can be eased, which improves the operator's control feeling. Below discussed is a
theoretical explanation of the hose volume control behavior.
At very low temperatures, the throttling effect of the orifice in the system is greatly affected, usually
causing delays in response. Let's suppose shifting the travel lever forward under low tempera-
tures, for example. Possibly the machine may fail to respond quickly or it may take too much time
to get started. In such cases, preferably remove the hose volume control for better damping effect,
and install the plug attached on previous models. Keep in mind, however, that the higher the oil
temperature rises, the quicker the reaction becomes.
3.2
350mm length) added.
Light weight type
Shape change
Shape change
Snap ring removed
Casting iron to steel iron
II - 57
II Service Engineering Section
G 3/8, hex. 8