Daewoo D20-2, Specifications Systems Operation Testing & Adjusting Disassembly & Assembly

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Relief Valve
(1) Spring. (2) Spool. (3) Poppet.
(4) By-pass Flow Control Orifice.
(5) Flow Control And Relief Valve.
(6) Spring.
(7) Sensing Orifice.
(8) Control Valve Sensing Orifice.
Operation of the relief valve feature is shown in
above figure. When an operating spool is shifted,
fluid is ported into the system and the by-pass is
blocked.
Above figure A shows operation at less than the relief
valve setting. There is no flow over the by-pass
orifice, so full system pressure is sensed at the spring
end of the control valve, as well as the opposite end.
The valve is thus hydraulically balanced and the large
spring holds the relief spool closed.
Maximum pressure is determined by the setting of
the small spring inside the control valve assembly.
When system pressure is sufficient to overcome this
heavy spring, the poppet is forced off its seat (see
above figure B).
Fluid immediately flows past the poppet to the tank
passage. This flow creates a pressure drop across
the sensing orifice and the control valve is no longer
hydraulically balanced.
When pressure drop across the sensing orifice is
great enough to overcome the force of the large
spring, the valve spool shifts, permitting flow to the
tank passage.
Relief valve sub-assemblies in the inlet section are
pre-set and tested by Vickers for given pressure
settings. Selection of the relief valves setting is based
on the work requirements of the system.
If a different relief valve setting is required, the valve
sub-assembly should be replaced,
Check Valve
(1) Spring. (2) Spool. (3) Poppet.
(4) By-pass Flow Control Orifice.
(5) Flow Control And Relief Valve.
(6) Spring.
(7) Sensing Orifice.
(8) Control Valve Sensing Orifice.
Timing of the spools is such that one cylinder port
opens to pressure and the other port opens to
reservoir before the by- pass passage is
completelyblocked.
To prevent return flow from passing into the pressure
passage and escaping through the partially closed
by-pass, check valves are provided in each operating
section except sections with
“
B
”
spool.
The check valves prevent the load from dropping.
21 of 29 New Hydraulic Systems Systems Operation
IDCS014B
Model
D20-2, D20S-2,
G20S-2, GC20S-2
D25-2, D25S-2
G25S-2, GC25S-2
D30S-2, G30S-2
GC30S-2
Part
Number
D144363
D144364
D144365
Setting
Pressure
2625 psi
(18,100 kPa)
2825 psi
(19,478kPa
3125 psi
(21,546 kPa)
IDCS014B