Fiat Kobelco EX355 Tier2, Technical Manual

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T3-3-14 EX355
CONTROL VALVE
MAIN RELIEF VALVE
The main relief valve prevents the main circuit pres-
sure from increasing more than the designed pres-
sure. When traveling and/or the power boost switch is
ON, the relief valve set pressure is increased. (Refer
to the Control System group in the SYSTEM section.)
Normal Relief Operation
The main circuit pressure in port HP acts on pilot
poppet (
4 ) via orifice ( 1 ) in main poppet ( 2 ). When
pressure in port HP increases more than the set force
of spring B (
5 ), pilot poppet ( 4 ) is unseated, allowing
pressure oil to flow to hydraulic oil tank port LP via
passage (
9 ). Then, pressure in oil chamber ( 3 ) is
reduced, developing a pressure difference between
port HP and oil chamber (
3 ) by orifice ( 1 ). When the
pressure difference increases more than the set force
of spring A (
10 ), main poppet ( 2 ) is unseated, allowing
the pressure oil to flow from port HP to port LP.
Relief Operation When Set-Pressure is Increased
When traveling and/or power boost switch is ON, the
pilot pressure is routed in port SG. The pilot pressure
pushes piston (
7 ) to the left via passage ( 6 ) in sleeve
( 8 ), increasing the set force of spring B ( 5 ). Then, the
higher pressure is required to open pilot poppet ( 4 ),
resulting in the relief set pressure to increase higher
than normal.
SG
SM6056
LP
HP
LP
HP
SM6057
SM6056
LP
HP
SM6055
LP
SG
HP
1 - Orifice
2 - Main Poppet
3 - Oil Chamber
4 - Pilot Poppet
5 - Spring B
6 - Passage
7 - Piston
8 - Sleeve
9 - Passage
10 - Spring A