Function And Structure - Kubota KX080-4 Workshop Manual

KX080-4, WSM

(2) Function and Structure

[A] Function
The pilot valve is the valve that controls the direction and volume of the stroke of the control valve, and lowers the
primary pressure from the unload valve to a secondary pressure only as much as is necessary to move the control
valve spool.
[B] Operation
1. When the control lever or pedal is in neutral
The force of the secondary pressure spring (1) does
not press on the spool (2). As a result, the spool is held
in a neutral position by the return spring (3). At such time,
the output ports (ports to the control valve port) port 1 (a)
and port 2 (b)) and port T (T) are connected.
2. When a control lever or pedal has been actuated
The cam (4) is turned counterclockwise, the port 1
side pushrod (5) presses down on the spool (2) via the
spring seat (6) and the secondary pressure spring (1).
When doing so, port P (P) and port 1 (a) are connected,
so the oil from the pilot pump flows through port 1 to the
control valve.
The pressure at port 1 rises until it is equivalent to the
force of the secondary pressure spring, thus balancing
the hydraulic pressure on the spool with the tension of
the secondary pressure spring and maintaining a fixed
port 1 pressure.
(1) Secondary pressure spring
(2) Spool
(3) Return spring
(4) Cam
(5) Pushrod
(6) Spring seat
3-M48
HYDRAULIC SYSTEM
RY9212001HYM0001US0
(a) Port 1
(b) Port 2
(P) Port P
(T) Port T
RY9212148HYM0011US0
KiSC issued 08, 2015 A