Fiat Kobelco EX355 Tier2, Technical Manual

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T3-4-8 EX355
PILOT VALVE
• Travel Pilot Valve
In neutral
(Corresponding to A to B in the output diagram):
Lever - In Neutral (Pusher Stroke: A to B)
In neutral, spool ( 6 ) closes port P (the input port) and
tank port T is connected to delivery port through
clearance (A). Thus, the pressure at delivery port is the
same as that at tank port T.
When the control lever is moved slightly from A to B,
pusher (
2 ) and spring guide ( 3 ) together move down
against return spring ( 5 ) and balance spring ( 4 ). At this
time, as both oil pressures above and below spool ( 6 )
are the same as the tank pressure, spool ( 6 ) moves
down together with spring guide ( 3 ) until clearance (A)
becomes zero.
Operation corresponding to the control lever stroke
(Corresponding to C to D in the output diagram):
Lever - Operated
(Pusher Stroke: C to D — Metering)
When the control lever is moved further to push pusher
(
2 ) down, port P is connected to delivery port through
notch (B) and passage in spool ( 6 ), routing pilot pump
pressure. However, when the pressure applied into
spool (
6 ) overcomes the balance spring force, spool
( 6 ) moves up, closing port P. When pusher ( 2 ) is
moved further down, compressing return spring ( 5 ) and
balance spring ( 4 ), the larger the balance spring force;
thus, the output pressure increases in proportion to the
increase in the balance spring force.
Full stroke operation:
Lever - Full Stroke (Pusher Stroke)
When the control lever is moved full stroke, pusher ( 2 )
is moved down until spring guide ( 3 ) comes into
contact with the shoulder of the valve casing (Lever
Stroke End), opening notch (B) further to port P.
The output pressure (pilot pressure to the control
valve) remains at the pilot system pressure (the port
P pressure).
Dimension (C) in the figure right shows the control
lever full stroke.
Delivery port
pressure
(Pilot pressure)
OUTPUT DIAGRAM
D
C
A B
Pusher stroke
SM0072