Eaton Vickers DG3V-8 Series - Page 8

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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.
Closed Center
- All Ports Closed
TAPB
AB
PT
B. Type ‘3’ spool is designed with ports (A) and (T)
interconnected and ports (P) and (B) blocked in the
center position.
Pressure and ‘‘B’’ Closed -
‘‘A’’ Open to Tank
TAPB
AB
PT
C. Type ‘6’ spool is interconnected at ports (A), (B) and
(T). Port (P) is blocked in the center position.
Pressure Closed -
‘‘A’’ & ‘‘B’’ Open to Tank
TAPB
AB
PT
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.
Pressure and ‘‘A’’ Closed
- ‘‘B’’ Open to Tank
TAPB
AB
PT
E. Type ‘33’ spool provides controlled leakage from port
(A) and (B) to port (T). Port (P) is blocked in the center
position.
Closed Center
- Bleed ‘‘A’’ & ‘‘B’’
TAPB
A
B
PT
)( )(
F. Type ‘52’ spool
Closed Center,
Regen. by Solenoid ‘A’
TAPB
AB
PT
G. Type ‘521’ spool
Closed Center,
Regen. by Solenoid ‘B’
TAPB
AB
PT