Samson 3277 Mounting And Operating Instructions page 3

Fail-safe action
When the signal pressure fails, the fail-safe
action of the actuator depends on whether
the springs are installed in the top or bottom
diaphragm chamber.
Actuator stem extends
When the signal pressure is reduced or the
air supply fails, the springs move the actua-
tor stem downwards and close the valve.
The valve opens when the signal pressure is
increased enough to overcome the force ex-
erted by the springs.
4
7
1 Nut
1.1 Nut
2 Actuator stem
3 Vent plug
4 Loading pressure 9
connection
2
5 Top diaphragm
case
6 Springs
7 Diaphragm plate
8 Diaphragm
9 Nuts and bolts
10 Yoke with bottom
diaphragm case
11 Loading pressure
connection
12 Stem seal
12.1Dry bearing
13 Wiper
15 Ring nut
16 Stem connector
Fig. 3 · Sectional diagram of Type 3277 with 240, 350 and 700 cm² effective diaphragm area
5
1.1
Dimension a
350 cm² = 209 mm
700 cm² = 246 mm
Design and principle of operation
Actuator stem retracts
When the signal pressure is reduced or the
air supply fails, the springs move the actua-
tor stem upwards and open the valve. The
valve closes when the signal pressure is in-
creased enough to overcome the force ex-
erted by the springs.
1 6 6.1
3
8
12
12.1
11
10
12.1
15
13
16
3
EB 8311 EN