Design And Principle Of Operation; Fail-Safe Positions - Samson 3249 Mounting And Operating Instructions

Design and principle of operation

3 Design and principle of oper-
ation
The Type 3249 Angle Valve is preferably
combined with either a Type 3271 Pneumat-
ic Actuator or a Type 3277 Pneumatic Actu-
ator with integral positioner attachment.
The standard valve has a ball body design
with clamp connection of the bonnet without
packing. The stem is sealed by an EPDM di-
aphragm with PTFE facing. The standard
valve has a bar stock body in valve size
DN 15 to 100 with welding ends according
to DIN EN 10357 Series A or NPS ½ to 4
with welding ends according to BS 4825.
Special versions of the bar stock version are
available in DN 15 to 80 or NPS ½ to 3, up
to K 60, with bolted-on valve bonnet and
VS
additional PTFE V-ring packing.
The valve is suitable for aseptic applications.
It has a valve body designed without cavi-
ties, allowing it to be cleaned or sterilized
prior to the production process according to
the CIP (clean-in-place) or SIP (steriliza-
tion-in-place) method.
The pressure of the special valve version with
packing (4.2) can be monitored at the test
connection (4.4).
The medium flows through the valve in the
direction indicated by the arrow. The plug
(3) is moved by changing the signal pressure
acting on the diaphragm of the actuator
(8.4).
The plug stem (6) is connected to the actua-
tor stem (8.1) by the stem connector (7). The
plug stem is sealed by the diaphragm (6.3)
14
and in the special version additionally by the
backup packing (4.1, 4.2, 4.3).

3.1 Fail-safe positions

The fail-safe position of the control valve up-
on air supply or control signal failure de-
pends on the actuator used (see associated
actuator documentation).
Depending on how the compression springs
are arranged in the SAMSON Type 3271
and Type 3277 Pneumatic Actuator, the
valve has one of two different fail-safe posi-
tions:
Actuator stem extends (FA)
When the signal pressure is reduced or the
air supply fails, the springs move the actua-
tor stem downward and close the valve. The
valve opens when the signal pressure is in-
creased enough to overcome the force exert-
ed by the springs.
Actuator stem retracts (FE)
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 exert-
ed by the springs.
Tip
The direction of action of the Type 3271 and
Type 3277 Pneumatic Actuator can be re-
versed, if required. Refer to the mounting
and operating instructions of the pneumatic
actuator:
u EB 8310-X for Type 3271 and Type 3277
EB 8048 EN