Samson 3372 - Signal Pressure Routing; Fail-Safe Action; Version with Direction of Action Stem Extends

3-4 EB 8313-3 EN
Design and principle of operation
3.2 Signal pressure routing
The signal pressure of the mounted
Type3725 Positioner is routed through the
corresponding port in the support element.
Actuator stem extends (FA)
In the "actuator stem extends" version, the
signal pressure is routed directly through the
support element to the bottom diaphragm
chamber and moves the actuator stem up-
ward opposing the spring force (see
Fig.3-3).
Actuator stem retracts (FE)
The support element of the version with fail-
safe action "actuator stem retracts" has a
borehole at the side. The signal pressure is
routed to the top diaphragm chamber over
external piping and moves the actuator stem
downward opposing the spring force (see
Fig.3-4).
3.3 Fail-safe action
When the signal pressure is reduced or the
control signal fails, the fail-safe position of
the control valve (see section3.1) depends
on whether the springs are installed in the
top or bottom diaphragm chamber.
3.3.1 Version with direction of
action "stem extends"
When the signal pressure is reduced or the
control signal fails, the springs move the ac-
tuator stem downward and close the globe
valve. The valve opens when the signal pres-
sure is increased enough to overcome the
spring force.
Fig.3-3: Signal pressure routing for
"actuator stem extends" (FA)
Fig.3-4: Signal pressure routing for "actuator stem
retracts" (FE)