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Design and principle of operation
2 Design and principle of oper-
ation
The Type 3252 Valve with a globe-style or
angle-style body can be combined with
either a Type 3271 Pneumatic Actuator or a
Type 3277 Pneumatic Actuator with integral
positioner attachment.
The standard valve bodies have threaded
ends with either G or NPT thread.
Special valve versions are designed with
either weld-on flanges or welding ends for
welding into the pipeline.
The modular design allows the actuators to
be exchanged and an insulating section or
metal bellows to be fitted to the standard
valve version
The medium flows through the valve in the
direction indicated by the arrow. The plug is
moved by changing the signal pressure act-
ing on the diaphragm of the actuator. The
plug stem (6) is connected to the actuator
stem (8.1) by the stem connector (7).
The plug stem is sealed by a spring-loaded
V-ring packing (4.2).
6
2.1 Fail-safe position
Depending on how the springs are arranged
in the actuator, the control valve assumes
one of two different fail-safe positions:
Actuator stem extends (fail-close): When the
pressure is relieved from the diaphragm or
the supply air fails, the actuator springs close
the valve.
Actuator stem retracts (fail-open): When the
pressure is relieved from the diaphragm or
the supply air fails, the actuator springs
open the valve.
2.2 Replacing the actuator
A pneumatic actuator can be replaced by
another pneumatic actuator in a different
size.
If the travel range of the actuator is larger
than the travel of the valve, the springs in the
actuator are preloaded by SAMSON so that
the travel ranges match.
EB 8053 EN
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