Eaton Vickers DG3V-8 Series Overhaul Manual page 11

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 spool in the last position
attained and the main stage spool remains in its last position.
WARNING
If pilot pressure fails or falls below the minimum
requirement of 5 bar (75 psi), 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. Figure 7 illustrates the spool/spring
arrangement on detent models.
Detent
A
Pilot
Solenoid
T A
Main Stage
Solenoid ''A'' is energized and shifts pilot spool to the right.
1.
Which causes main stage spool to shift left. Oil flow
2.
from P³A and B³T is obtained.
Main stage spool remains in position attained due to pilot
3.
valve detent until solenoid ''B'' is energized. (Note: If pilot
pressure fails, the main stage will shift to center position.
Figure 7. Detented ''N'' Model
E. Optional Features (Main Stage)
Control of the mainstage spool travel can be modified with
certain optional features. The most common features are
discussed in the following paragraphs.
1. Stroke Limiter Adjustment (Fig. 8): Main stage spool
travel can be limited by using stroke adjust covers. Stroke
adjust covers may be used on one or both ends of the main
stage section. When the stroke is limited, maximum flow
through the valve is reduced (assuming same inlet pressure).
This slows the actuator movement.To limit the spool travel,
loosen the jam nut and turn adjusting screw clockwise.
F
B
P
B A
P B T
4
Main
Stage
Spool
3
2
Part No. Part Name
1 Cover
2 Spring
3 O-Ring
4 Back-up Ring
Figure 8. Stroke Adjuster Feature
2. Pilot Choke Option (Fig. 9): A pilot choke increases the
amount of time it takes to shift the main stage spool from
one position to another. Increasing shift time lowers the
possibility of developing large flow transients in the circuit. A
pilot choke is designed to allow free flow to one end of the
main stage spool but restricts flow out of the opposite end.
The rate of spool travel, in either direction, can be slowed by
loosening a locknut and turning an adjusting screw
clockwise. To increase the rate of spool travel, turn the
adjusting screws counterclockwise. When a pilot choke is
used, pilot pressure should be taken from a constant
pressure source. The pilot choke is mounted between the
pilot valve and the main stage sections.
9
10
11
12
13
14
Part No. Part Name
1 Retaining Ring
2 Nut
3 Adjusting Screw
4 ''O'' Ring
5 Back-up Ring
6 Needle Housing
7 ''O'' Ring
Figure 9. Pilot Choke
5
6
7
1
Part No. Part Name
5 Piston
6 Jamnut
7 Adjuster Screw
1
2
3
4
5
6
7
8
Part No. Part Name
8 Back-up Ring
9 Needle
10 Spring
11 Sleeve
12 Body
13 Dowel Pin
14 ''O'' Ring
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