23
Section V – Internal Valve Functions
A. General
To insure the proper application of a two stage valve, pilot
pressure, pilot drain and integral check valve options must
be considered. The following paragraphs (B through D)
discuss these options.
B. Pilot Pressure
1.
Internal Pilot Pressure (Standard)
: Internal pilot
pressure can be obtained in two ways and must be
tailored for the application. Models with closed center type
spools automatically provide internal pilot pressure.
Models that use open center type spools require a check
valve in the pressure (P) port to maintain minimum pilot
pressure. In most cases, maximum internal pilot pressure
is rated to 210 bar maximum (3000 psi). Minimum pilot
pressure ratings are noted in the installation drawings
(see Table 1).
2.
External Pilot Pressure
: When pilot pressure from a
separate source is used, it must be connected to the “X” port
(external pilot pressure connection). Models that use exter-
nal pilot pressure do not require a check valve at the pres-
sure port. External pilot pressure models are identified with
the letter “E” stamped into the unit nameplate (i.e.
DG5S4-062***E-51). Maximum external pilot pressure is
also rated at 210 bar (3000 psi).
3.
Pilot Pressure Conversions
: If it is necessary to
convert your unit from external pilot pressure to internal pilot
pressure or vice versa, internal plug(s) must be removed or
added to the main stage body. See the figures noted in Table
8 for internal plug locations.
4.
Pressure Centered “D” Models (H06 & -10
Series only)
: A pre-set pilot pressure can be obtained in
these models. Refer to the model code in Table 2 for
pressure settings. Pilot pressure can be increased or
decreased by simply changing internal plugs in the main
stage body. Refer to plug table in parts drawing for part
numbers and see the figure noted in Table 8 for internal
plug locations.
C. Pilot Valve Drains
1.
Internal Drain
: Internal drain models are used when
pressure surges in the tank line are small and CAN NOT
overcome pilot pressure.
To shift a pilot spool, pilot pressure must always exceed tank
pressure by a minimum amount. Figure 14 is an example
showing pilot pressure vs. tank pressure. Refer to the unit
installation drawing for minimum pressure ratings. Internal
pilot drain models have the letter “T” stamped on the unit
nameplate (i.e. DG5S4-062-**t-51).
NOTE
A 150 psig
∆
P must always be maintained to
shift closed center pilot spools. A 75 psig
∆
P
must always be maintained to shift open center
pilot spools.
PIlot Pressure (1000 psig)
This tank line pressure subtracts
form the applied pilot pressure.
Figure 14. Pilot Valve - Internal Drain
1000
900
800
700
600
500
400
300
200
100
0
NOTE
Tank Line Pressure Surge (850 psig)
Tank Line Pressure (750 psig)
150
psig
∆
P
2.
External Drain (Standard)
: External drain models are
recommended if pressure surges in the tank line CAN over-
come pilot pressure. Drain connection “Y” is used for external-
ly drained models. Pressure centered “D” models use two
drain connections “Y” and “W”. All external drain connections
MUST be piped directly to tank through surge free lines. Refer
to the installation drawing (Table 1) for further information.
3.
Drain Conversions
: If it is necessary to convert your
unit from external drain to internal drain or vice versa, an
internal “T” plug must be added or removed to the main body
section. Figures 23c, 24c, 25c, 26c, and 27c show internal
“T” plug locations on various models.
D. Integral Check Valves
Check valves are located within the pressure port of the
main stage section. The purpose of the check valve is to
develop back pressure, at the pressure port, when open
center or tandem main stage spools are used. Back
pressure is necessary to maintain internal pilot pressure
when the main stage spool shifts to open center position.
Table 4 indicates when an integral check valve is required.
Pilot Pressure
Source
Yes
0, 1, 4, 8, 9, 11
No
2, 3, 6, 31, 33
External
No
All Spools
Table 4. Integral Check Valve Circuit Requirements
Integral Check
Valve Req’d
Main Stage
Spool Type
Internal
Integral check valves are applicable at various cracking pres-
sure ranges. Refer to the model code in Table 2 for check
valve pressure ranges. The unit nameplate identifies which
check valve is used (i.e. DG5S4-062-***K*-51). Refer to instal-
lation drawing (Table 1) for additional check valve information.
NOTE
As an alternate to the integral check valve, a 50/75
psi check valve can be installed in the tank line of
the valve to obtain pilot pressure.
