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Design and principle of operation
The connection between the actuator stem
and the valve's plug stem differs depending
on the valve used. Refer to the mounting and
operating instructions of the corresponding
valve for more details.
3.1 Direction of action
The direction of action is determined by how
the springs are arranged in the actuator and
its internal design.
− Actuator stem retracts (FE)
− Actuator stem extends (FA)
Note
It is not possible to reverse the operating di-
rection.
3.2 Fail-safe action
Depending on the operating direction of the
actuator, the actuator has different fail-safe
actions that become effective when the sup-
ply air fails.
Actuator stem extends
When the air supply fails, the spring force
moves the stem downwards to the end posi-
tion causing the globe valve on which the
actuator is mounted to close. The valve
opens when the signal pressure is increased
enough to overcome the spring force.
Actuator stem retracts
When the air supply fails, the spring force
moves the stem upwards causing the globe
valve on which the actuator is mounted to
open. The valve closes when the signal pres-
3-2
sure is increased enough to overcome the
spring force.
3.3 Versions
− Type 3379-00: Type 3379 Actuator
combined with Type 3724 Electropneu-
matic Positioner (u EB 8395)
− Type 3379-01: Type 3379 Actuator for
on/off service
− Type 3379-02: Type 3379 Actuator
combined with Type 4740 Electric Limit
Switch (u EB 8357)
3.4 Accessories
Vent plugs
Vent plugs are screwed into the exhaust air
ports of pneumatic and electropneumatic de-
vices. They ensure that any exhaust air that
forms can be vented to the atmosphere (to
avoid excess pressure in the device). Further-
more, the vent plugs allow air intake to pre-
vent a vacuum from forming in the device.
u AB 07
3.5 Technical data
The housing inscription provides information
on the actuator version (see the 'Markings
on the device' section).
Note
More information is available in the follow-
ing valve data sheets:
− Type 3347: u T 8097
− Type 3349: u T 8048-2 and u T 8048-22
− Type 3321CT: u T 8115
EB 8315 EN
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