Design And Principle Of Operation; Fail-Safe Position - Samson 3256 Mounting And Operating Instructions

3 Design and principle of oper-
ation
The Type 3256 Angle Valve is preferably
combined with a SAMSON Type 3271 or
Type 3277 Pneumatic Actuator (see
Fig. 3-1). It can also be combined with other
actuators.
The seat (4) and plug with plug stem (5) are
installed in the body (1). The plug stem is
connected to the actuator stem (A7) by the
stem connector clamps (A26) and is sealed
by a spring-loaded V-ring packing (15).
Alternatively, an adjustable high-
temperature packing can be used.
The springs in the pneumatic actuator are
located either above or below the
diaphragm (A4) depending on the selected
fail-safe action. A change in the signal
pressure acting on the diaphragm causes the
plug to move. The actuator size is
determined by the diaphragm area.
The medium flows through the valve in the
direction indicated by the arrow. A rise in
signal pressure causes the force acting on
the diaphragm in the actuator to increase.
The springs are compressed. Depending on
the selected direction of action, the actuator
stem retracts or extends. As a result, the plug
position in the seat changes and determines
the flow rate through the valve.
The direction of flow is different for the ver-
sion with a ceramic anti-wear sleeve: the
medium flows through the valve in the flow-
to-close direction.
EB 8065 EN

Design and principle of operation

3.1 Fail-safe position

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 actuator's direction of action 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
3-1