14
3.
Spring Offset
: Single stage spring offset models use
one spring to return the spool to an offset position. In two-
stage models, the spring and washer is removed from the
main stage and offset action is obtained from the pilot valve.
Offset pilots have a solenoid removed from the spring end of
the valve. Spring offset pilots control the main stage when the
solenoid is de-energized, through spring action, so long as
pilot pressure is available. Spring offset valves have the letter
“A” stamped into the nameplate (i.e. DG5S4-062A-**-51).
Figure 6 illustrates an offset two-stage valve.
4.
Pressure Centered
: Pressure centered valves
provide a more positive centering arrangement than normal
spring centered valves. This is a accomplished in the follow-
ing manner:
Assume both pilot valve solenoids are de-energized and the
main stage spool is positioned to the left (see Figure 7). Pilot
pressure is applied to both ends of the main stage from the
number seven (7) pilot spool. The sleeve moves to the right
under the influence of the spring and pilot pressure until the
piston shoulder is contacted. Since the sleeve and piston
areas are greater than the total spool area at the right hand
end of the valve, the sleeve continues to move to the right
carrying the piston with it until it contacts the valve body
(center position).
Assume the main stage spool was positioned to the right
with both pilot valve solenoids de-energized, pilot pressure is
applied to the sleeve and piston areas on the left side but the
sleeve is bottomed against the valve body at this time. Only
the piston area applies force to the left end of the spool.
Since the spool land area at the right side is greater than the
piston area, the spool will be forced to the left until the piston
shoulder butts against the sleeve (center position).
If pilot pressure falls below 150 psig, the centering springs
will cause the spool to center within the valve body.
Pressure centered valves are not available with integral
check valves. (Refer to Section V, Internal Valve Functions,
for integral check valve information.) Pressure centered
models have the letter “D” stamped into the unit nameplate
(i.e. DG5S4-062D-**-51). Figure 7 illustrates spool/spring
arrangement on pressure centered models.
NOTE
A fifth condition of the main stage spool can be
obtained through use of a detent pilot stage. Refer
to the following paragraph.
5.
Detent Valve Operation
: Detent valve operation can
be achieved by installing a detent into the pilot valve. A
detent is assembled on one or both ends of the pilot spool
depending on the type of pilot valve used. When a pilot valve
solenoid is de-energized, the detent holds the pilot spoolin
its last position attained and the main stage spool remains in
its last position.
CAUTION
If pilot pressure fails or falls below the minimum
requirement of 75 PSIG, the main stage spool will
shift to center position even though the pilot valve
remains in the last detent position. For this reason,
flow conditions in center or neutral position must be
selected with care.
Detent models are indicated by the letter “N” stamped into
the unit nameplate (i.e. DG5S4-062N-**-51). Figure 8
illustrates the spool/spring arrangement on detent models.
Solenoid is
de-energized
Figure 6. Spring Offset “A” Model
P
B
Main Stage
T
A
P
B
T
A
B
The spring returns pilot
spool to “A” offset position
and shifts main stage
spool. Main stage oil flow
is P-A and B-T.
