Samson 3271-5, Mounting And Operating Instructions

Page: 14 / 52

14 EB 8310-1 EN
Design and principle of operation
3.1 Direction of action and
signal pressure routing
The direction of action for both Type 3271
and Type 3277 can be reversed (see sec
-
tion 6.3).
Type 3271‑5 (see Fig. 2)
In the "actuator stem extends" version, the
signal pressure is routed through the bottom
signal pressure connection (S) to the bottom
diaphragm chamber and moves the actuator
stem (A7) upward opposing the spring force.
In the "actuator stem retracts" version, the
signal pressure is routed through the top sig-
nal pressure connection (S) to the top dia-
phragm chamber and moves the actuator
stem (A7) downward opposing the spring
force.
Type 3277‑5 (see Fig. 3 and Fig. 4)
In the Type 3277-5 Actuator, the signal pres
-
sure is transmitted to the diaphragm cham-
ber through the holes on the left or right side
of the yoke and over a switchover plate
(A2.1, accessories, see Fig. 4). The fail-safe
action of the actuator ("actuator stem ex-
tends" or "actuator stem retracts") deter-
mines how the switchover plate must be
aligned with the marking (A2.5).
If the actuator is operated without a position-
er, a connecting plate (A2.1, accessories,
see Fig. 4) is required instead of the switcho
-
ver plate. In this case, the signal pressure is
routed directly over the signal pressure con-
nection (A2.9) of the connecting plate to the
diaphragm chamber.
Actuators with device index .01 are
equipped with new connecting plates. Old
and new connecting plates are not inter
-
changeable.
Accessories
Switchover plates and connecting plates are
listed as accessories.
With in-
dex
Order no.
Switchover
plate
New .01 1400-6822
Old .00 1400-6819
Connect-
ing plate
New .01 1400-6823
G thread .00 1400-6820
NPT thread .00 1400-6821
3.2 Fail-safe action
When the signal pressure is reduced or the
control signal fails, the fail-safe position of
the control valve depends on whether the
springs are installed in the top or bottom di-
aphragm chamber.
Version with fail-safe action "actuator stem
extends" (FA)
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.
Tip
Note