Takeuchi TB 250, Workshop Manual

Page: 93 / 352

3-12
3
FUNCTION
PILOT VALVE
PILOT VALVE
The pilot valve casing contains the vertical shaft holes that
incorporate the reducing valves. When the lever is tilted,
the push rod and spring seat are pushed down, changing
the spring force of the secondary pressure.
The casing contains the oil inlet port P (the primary pres-
sure) and the tank port T. The secondary pressure corre-
sponding to the changes in operating angle performed by
the lever (1) can be provided through the output ports A
and B located below the vertical shaft holes. The second-
ary pressure functions as the pilot pressure to actuate the
spool of the control valve (2).
When the lever (1) is at the neutral position:
The force of the spring (3) that determines the output pres-
sure (secondary pressure) of the pilot valve is not conveyed
to the spool (4). Therefore, the spool (4) is pushed up by
the return spring (5), and the output ports A and B are con-
nected with the tank port T, making the pressures in the
ports A and B equal to the pressure in the tank port T.
When the lever (1) is tilted:
When the lever (1) is tilted and the push rod (6) is pushed,
the spool (4) moves downward and the input port P is con-
nected with the output port A. Then, the oil from the pilot
pump flows into the output port A, generating a pressure.
When the lever (1) is kept at a certain position:
When the lever (1) is tilted and thereby the pressure in the
output port A increases to the level equivalent to the force
of the set spring (3) force, the hydraulic pressure becomes
balanced with the spring force. When the pressure in the
output port A becomes higher than the set force, the out-
put port A and the input port P are closed, while the output
A and the tank port T are opened. When the pressure in the
output port A becomes lower than the set force, the output
port A and the input port P are opened, while the output
port A and the tank port T are closed. Thus, the secondary
pressure is kept constant.
3KAC01Z
1
2
A
B
T P
3KAC02Z
1
5
3
4
A B
T
P
3KAC03Z
P
4
6
1
A B
3KAC04Z A B
P
T
3
1