12
Pressure and “B” Closed - “A” Open to Tank
Closed Crossover, Pressure to “T” with
“A” & “B” Blocked
Pressure Closed - “A” & “B” Open to Tank
A
P T
B
Type
3
A
P T
B
Type
4
A
P T
B
Type
8
Tandem, Open Crossover, Pressure to “T”
with “A” & “B” Blocked
Type
6
A
P T
B
Open Center, Partial - All Ports
“A” Closed - Pressure Open to Tank thru “B”
Pressure and “A” Closed - “B” Open to Tank
A
P T
B
Type
9
A
P T
B
Type
11
A
P T
B
Type
33
Closed Center - Bleed “A” & “B”
Type
31
A
P T
B
A
P
T
B
A
P
T
B
A
P
T
B
A
P
T
B
A
P
T
B
A
P
T
B
A
P
T
B
A
P
T
B
C. Methods of Spool Control, Main
Stage
1.
Manual Lever (all sizes except the DF*S4-16*
size)
: A manual lever arrangement is available for shifting
certain valves. The lever arrangement is connected to a
special valve end cover. A spool with an extension protrudes
through the cover and is acted upon by the lever. This allows
manual positioning of the spool within the body. Large valves
require considerable force to move the spool when it is
under pressure. For this reason, the two inch valve size is
not available with a manual lever control. Examples of valves
with the manual lever control are: DG17S4-06*A-50,
DG17S4-10*A-50, DG17S4-06*C-50, DG17V-3-*-40.
2.
Remote Pilot Source
: Main stage valves are avail-
able for use with a remote source. This means that the valve
is shifted from a remote pressure source by other valves in
the logic circuit. Examples of valves that use a remote
pressure source are: DG3S4-06*C-50, DG3S4-10*C-50 and
DG3S4-06*-50.
3.
Integral Pilot Valve
: The integral pilot type two stage
valve is a very common valve used in the field today. Two
stage valves allow large volumes of fluid to be switched to
and from an actuator with minimum power required for
control. Reference Figures 4 through 8, shown in the follow-
ing section.
D. Main Stage Spool Position
Main stage spools are positioned within the valve by special
arrangements. The four basic main stage spool positioning
arrangements are: no spring-floating, spring centered, spring
offset and pressure centered.
