Samson 3276-D, Mounting And Operating Instructions

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EB 8318 EN 3-1
Design and principle of operation
3 Design and principle of oper-
ation
See Fig. 3-1 to Fig. 3-5
The SAMSON Type 3276 Actuators are
mounted to Series 590 Valves (globe valves).
The actuator mainly consists of a housing
with yoke (40), top (850) and bottom (900)
diaphragm cases, diaphragm (911) with di-
aphragm plate (901), spring (595) with
spring plate (904) as well as actuator stem
(61).
The signal pressure p
st
creates the force F =
p
st
· A at the diaphragm surface A, which is
opposed by the spring in the actuator. The
bench range is determined by the spring
and its compression, taking into account the
rated travel. The travel is proportional to the
signal pressure p
st
. The direction of action of
the actuator stem (fail-safe action) depends
on the actuator version.
The stem connector (907) connects the actu-
ator stem with the plug stem of the globe
valve.
3.1 Direction of action
There are two versions of the Type 3276
Actuator which have different direction of
action. The direction of action is determined
by the actuator design.
− Version D (direct-acting, actuator stem
retracts)
With direction of action "actuator stem
retracts", the compressed air is applied
to the signal pressure connection on the
top diaphragm case (850) of the actua-
tor.
− Version R (reverse-acting, actuator stem
extends)
With direction of action "actuator stem
extends", the compressed air is applied
to the signal pressure connection on the
bottom diaphragm case (900) of the ac-
tuator.
Signal pressure routing
In the version D ("actuator stem retracts"),
the signal pressure is routed through the sig -
nal pressure connection (S) on the top dia -
phragm case (850) into the actuator and
moves the actuator stem (61) downward op-
posing the spring force.
In the version R ("actuator stem extends"),
the signal pressure is routed through the sig -
nal pressure connection (S) on the bottom di-
aphragm case (900) into the actuator and
moves the actuator stem (61) upward oppos-
ing the spring force.