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 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) or (4). At
such time, the output port (control valve port) (a) and port
T (T) are connected.
(1) Secondary Pressure Spring
(2) Spool
(3) Return Spring
(4) Return Spring
2. When the control lever has been actuated
When the control lever is actuated, the pushrod (1)
presses down on the spool (4) via the spring seat (2) and
the secondary pressure spring (3). In doing so, port P (P)
and the output port (a) are connected, so the oil from the
pilot pump flows through the output port to the control
valve.
The pressure at the output port 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 output port pressure.
(1) Pushrod
(2) Spring Seat
(3) Secondary Pressure Spring
(4) Spool
3-M43
HYDRAULIC SYSTEM
RY9212001HYM0001US0
(a) Output Port
(T) Port T
RY9212148HYM0005US0
(a) Output Port
(P) Port P
RY9212148HYM0006US0
KiSC issued 08, 2015 A