Eaton Vickers DG3V-8 Series Overhaul Manual page 8

2. Closed Center Spools (2, 3, 6, 31, 33, 52 and 521 types):
Closed center spools are used where two or more operations
are performed by a single pump or an accumulator. Closed
center valves prevent the loss of fluid from the pump or
accumulator when the spool crosses center.
A. Type '2' spool blocks ports (P), (A), (B) and (T) from
one another in the center position. The ports are
momentarily blocked during spool crossover.
T A
A B
P T
B. Type '3' spool is designed with ports (A) and (T)
interconnected and ports (P) and (B) blocked in the
center position.
T A
A B
P T
C. Type '6' spool is interconnected at ports (A), (B) and
(T). Port (P) is blocked in the center position.
T A
A B
P T
P B
Closed Center
- All Ports Closed
P B
Pressure and ''B'' Closed -
''A'' Open to Tank
P B
Pressure Closed -
''A'' & ''B'' Open to Tank
D. Type '31' spool is a type '3' spool reversed in the
bore. A type '31' spool is interconnected at ports (B) and
(T), but blocked at ports (P) and (A) in the center position.
T A P
A B
P T
E. Type '33' spool provides controlled leakage from port
(A) and (B) to port (T). Port (P) is blocked in the center
position.
T A P
A
B
)( )(
P T
F. Type '52' spool
T A P
A B
P T
G. Type '521' spool
T A P
A B
P T
B
Pressure and ''A'' Closed
- ''B'' Open to Tank
B
Closed Center
- Bleed ''A'' & ''B''
B
Closed Center,
Regen. by Solenoid 'A'
B
Closed Center,
Regen. by Solenoid 'B'
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