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Design and principle of operation
3 Design and principle of oper-
ation
The single-seated Type 3321CT Globe Valve
is preferably combined with a SAMSON
Type 3379 Pneumatic Actuator.
The seat (2) and plug with plug stem (3) are
installed in the body (1). The plug stem has a
thread to screw it onto the actuator stem and
is sealed by the spring-loaded packing (8).
The process medium flows through the valve
in the direction indicated by the arrow in the
flow-to-open direction. The plug position de-
termines the cross-sectional area between
the seat and plug.
12
The position of the plug is changed by the
control signal acting on the actuator.
3.1 Fail-safe positions
Depending on how the compression springs
are arranged in the pneumatic actuator, the
valve has two fail-safe positions that become
effective when the supply air fails:
− Fail-close: the valve is closed upon air
supply failure.
− Fail-open: the valve is opened upon air
supply failure.
8
1
7
2
10
3
14
4
4
13
7
8
1
3
10
2
13
14
Fig. 2: Type 3321CT Valve,
Body
Seat
Plug
Guide bushing
Valve bonnet
V-ring packing
Hexagon screw
Body gasket
Flange
DN 15 to 25
EB 8115 EN
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