Fail-Safe Action; Versions; Accessories - Samson 3276-D Mounting And Operating Instructions

Design and principle of operation

3.2 Fail-safe action

Note
The listed fail-safe actions apply to
SAMSON Series 590 Valves (globe valves).
When the signal pressure is reduced or the
supply air fails, the actuator version deter-
mines the direction of action and, as a result,
the fail-safe position of the valve.
Version with handwheel: in the active man-
ual mode (the handwheel is not in the neu-
tral position), the valve is not moved to the
fail-safe position even upon failure of the
supply air.
Actuator stem ex-
tends (version R, reverse-acting)
When the signal pressure is reduced or the
control signal fails, the spring moves the ac-
tuator stem downward and closes the globe
valve. The valve opens when the signal pres-
sure is increased enough to overcome the
spring force.
Actuator stem re-
tracts (version D, direct-acting)
When the signal pressure is reduced or the
control signal fails, the spring moves the ac-
tuator stem upward and opens the globe
valve. The valve closes when the signal pres-
sure is increased enough to overcome the
spring force.
3-8

3.3 Versions

The versions D and R of the Type 3276 Pneu-
matic Actuator are available with 258, 387,
645 and 1032 cm² actuator areas
Version with handwheel
All versions can be fitted with an additional
top-mounted handwheel (see Fig. 3-2 and
Fig. 3-5) or an additional side-mounted
handwheel (see Fig. 3-3). The actuator stem
position can be adjusted using the hand-
wheel.

3.4 Accessories

Note
Refer to the mounting and operating instruc-
tions of the valve accessories to be mounted
for more details on their attachment.
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).
Version R actuators are delivered with vent
plugs.
EB 8318 EN