Fiat Kobelco EX355 Tier2, Technical Manual

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EX355 T3-4-3
PILOT VALVE
OPERATION
• Front and Swing Pilot Valve
The lower face of spool ( 8 ) head is suspended by the
upper face of spacer ( 4 ); they are kept in contact by
setting force of balance spring ( 6 ). Spacer ( 4 ) is
installed between pusher ( 3 ) and spring guide ( 5 ) and
supported by return spring ( 7 ). Piston ( 9 ) is located
inside spool ( 8 ). The lower end of piston ( 9 ) makes
contact with the plate, preventing the piston from
moving further downward.
Above piston (
9 ), a chamber is provided and it is led to
the outside of spool ( 8 ) through holes provided in spool
( 8 ).
1 - Control Lever
2 - Cam
3 - Pusher
4 - Spacer
5 - Spring Guide
Delivery port
pressure
(pilot pressure)
A B
Pusher stroke
Port T
Delivery port
Port P
Section ( a )
4
5
6
7
8
9
(A)=0
(A)
1
2
3
SM0067
In neutral
(Corresponding to A to B in the output diagram):
When control lever ( 1 ) is in the neutral position (no
pusher stroke), spool ( 8 ) completely blocks pressure
oil from entering port P. Since the delivery port is open
to port T, pressure at the delivery port equals that in the
hydraulic oil tank.
When control lever (
1 ) is slightly moved, cam ( 2 )
moves together, pressing down on pusher ( 3 ).
Then, pusher ( 3 ), spacer ( 4 ), and spring guide ( 5 ) move
downward as a unit, compressing return spring ( 7 ).
The lower face of spool ( 8 ) is kept in contact with the
upper face of spacer ( 4 ) by setting force of balance
spring ( 6 ) and moves downward together with spacer
( 4 ). However, even if control lever ( 1 ) is moved further,
until clearance (A) at section (a) reaches zero, the
delivery port remains open to port T, keeping pressure
at the delivery port equal to that in the hydraulic oil
tank.
OUTPUT DIAGRAM
6 - Balance Spring
7 - Return Spring
8 - Spool
9 - Piston