Section Iv. Pilot Valve Section - Eaton Vickers DG3V-8 Series Overhaul Manual

Section IV - Pilot Valve Section
Figure 11. DG5V8 with DG4V-3(S) Pilot
A. Spool Type - Pilot Valve Section
To maintain proper control, closed center pilot spools are
normally used in two stage valves. In most cases, a number
''6'' type pilot spool is used.
When a type ''4'' or ''8'' main stage spool is used, the letter
''V'' is inserted into the pilot valve model code.
B. Spool Positioning - Pilot Valve Section
Pilot spools are positioned within the valve by special spool
arrangements. The three basic pilot valve spool arrangements
are spring centered, spring offset and detents. The following
paragraphs (1 through 3) describe pilot spool arrangements.
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 deenergized 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 position. In
this model, a solenoid is completely removed from the spring
end of the pilot valve.
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. The detent(s) hold the
pilot spool in the last position attained until the opposite
solenoid is energized.
C. Methods of Control - Pilot Valve
The following pilot control methods are available for pilot
spool position.
Control Model Codes
Electrical Solenoid DG4V-3, DG4V-3S
1. Remote Pilot: Pilot valves, such as a DG4V-3, 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
drawing 5007.04/EN/0496/S.
2. 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).
Figure 12a. Flow Conditions
Pressure to ''B'' - ''A'' to Tank
Figure 12b. Flow Conditions
Pressure to ''A'' - ''B'' to Tank
Figure 12c. Flow Conditions
Flow Blocked (Center Condition #2 Spool)
CAUTION
DO NOT energize both (AC) solenoids
simultaneously. Sustained operation with both
solenoids energized will cause excessive
current in the coil and accelerates burnout.
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