19
1.
Spring Centered
: A spring and washer are installed
at each end of the pilot valve spool. The spring moves the
spool until the washer contacts the end of the valve body. In
the de-energized condition of the pilot valve, the spool is
held in center position within the body by the springs and
washers.
2.
Spring Offset
: Spring offset models use one spring
and washer to return the pilot valve spool to an offset posi-
tion. In this model, a solenoid is completely removed from
the spring end of the pilot valve. Solenoid operating power is
reduced by the sacrifice of the center spool position.
3.
Detents
: A detent mechanism is installed on one or
both ends of the pilot valve spool. Detent valve solenoids
can be momentarily energized to the correct position and
then power may be removed from the solenoid. This reduces
the input control power below that of an offset model. The
detent(s) hold the pilot spool in the last position attained until
the opposite solenoid is energized. As in the offset valve,
solenoid power is reduced by the sacrifice of the center
spool position.
C. Methods of Control - Pilot Valve
The following pilot control methods are available for pilot and
spool position.
Manual Lever/Roller
Remote Pilot
Air Type Solenoid
DG17/20V-3
DG3V-3
DG18V-3, DG18S4-01
DG4S4-01, DG4S4-01-W, W,
DG4V-3
Control
Model Codes
Electrical Solenoid
1.
Manual Lever/Roller
: A manual lever 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 pilot valve spool within
the body. In some valves a roller is used instead of a lever to
actuate the pilot spool.
2.
Remote Pilot
: Pilot valves, such as a DG3V-3-*40,
are available for use with a remote pilot source. This means
that a valve can be shifted from a remote pressure source by
other valves in the logic circuit. Refer to service parts draw-
ing I-3871-S.
3.
Air Type Solenoids
: Air operated pilot valves are
actuated with air pressure through a connection plate.
A DG18V-3-C-40 or DG18S-01-L-52 air type valve can be
used to control the main stage of a DG19S4-062C-**-51 two
stage unit (see Figure 11a). When air pressure (50 psi mini-
mum) enters the pilot valve air chamber, the piston moves
the pilot spool. This allows control flow to enter the main
stage section (see Figure 11b).
Pilot Stage Valve DG18S4
Directional Valve
Air
Connection
#1
Pilot Choke
(When
Req’d)
DG19S4-06**-*-52
DG19S4-H06**-*-52
DG19S4-10**-*-52
Air
Connection
Plate
DG3S4 Main Stage Valve
Air
Connection
#2
11a. DG19S4-**-52 Two Stage Valve
The DG18S4-06 and DG18S-8 air operated valves do not
use a pilot stage but are shifted directly by large air pistons
located at each end of the spool. The air pistons operate
similarly to those of the DG18S4-01* pilot shown in Figure
11b. A connection plate is required to feed air to the pistons.
4.
Electrical Solenoid Pilot Operation
: Electrical
solenoids are attached to the pilot valve body. Internal push
pins connect the solenoid to the pilot spool. When the
magnetic field of solenoid “B” is energized, the solenoid
armature moves the push pin and shifts the pilot spool
towards solenoid “A” (see Figure 12a). When solenoid “A” is
energized, the pilot spool shifts toward solenoid “B” (see
Figure 12b). When both solenoids are de-energized, the pilot
spool shifts to center position (see Figure 12c).
