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3 Design and principle of oper-
ation
The Type 3371 Pneumatic Actuators have an
actuator area of either 120 or 350 cm².
They are mainly used for attachment to
SAMSON Series V2001 Valves:
− Type 3321 Globe Valve
− Type 3323 Three-way Valve
− Type 3531 Globe Valve for Heat Transfer
Oil
− Type 3535 Three-way Valve for Heat
Transfer Oil
Table 3-1 provides an overview of the possi-
ble combinations and how the actuator is
mounted on the valve.
The pneumatic actuators mainly consist of
two diaphragm cases, a diaphragm and in-
ternal springs. The actuator is connected to
the valve bonnet using a rod-type yoke. The
stem connector clamps connect the actuator
stem with the plug stem of the valve.
The signal pressure p
p
· A at the diaphragm surface A, which is
st
opposed by the springs in the actuator. The
bench range is determined by the number of
springs used and their compression, taking
into account the rated travel. The travel is
proportional to the signal pressure p
3.1 Direction of action
The direction of action is determined by how
the springs and diaphragm plate are ar-
ranged in the actuator. With direction of ac-
tion "actuator stem retracts", the compressed
air is applied to the signal pressure connec-
EB 8317 EN
creates the force F =
st
.
st
Design and principle of operation
tion on the top diaphragm case. With direc-
tion of action "actuator stem extends", the
compressed air is applied to the signal pres-
sure connection on the bottom diaphragm
case.
The direction of action can be reversed (see
the 'Service and conversion work' section).
3.2 Signal pressure routing
3.2.1
120 cm² actuator area
See Fig. 3-1
In the "actuator stem extends" version, the
signal pressure is routed through the bottom
signal pressure connection (A35) to the bot-
tom diaphragm chamber and moves the ac-
tuator stem (A3) upward opposing the
spring force.
In the "actuator stem retracts" version, the
signal pressure is routed through the top sig-
nal pressure connection to the top dia-
phragm chamber and moves the actuator
stem (A3) downward opposing the spring
force.
3.2.2
350 cm² actuator area
See Fig. 3-2
In the "actuator stem extends" version, a sig-
nal pressure connection (S) is located on the
side of the yoke which is connected to the
bottom diaphragm chamber over an internal
hole. The signal pressure moves the actuator
stem upward opposing the spring force. A
positioner can be connected using a connec-
tion block at this point. No additional piping
3-1
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