Design And Principle Of Operation - Samson EB 8015 EN Mounting And Operating Instructions

3 Design and principle of oper-
ation
See Fig. 3-1 and Fig. 3-2 on page 3-2.
The Type 3241 Valve is a single-seated
globe valve. This valve is preferably com-
bined with a SAMSON Type 3271 or
Type 3277 Pneumatic Actuator. It can also
be combined with other actuators.
The seat (4) and plug with plug stem (5) are
installed in the body (1). In some versions,
the seat is already integrated into the body.
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 (16). The springs in the pneu-
matic actuator (A) are located either above
or below the diaphragm depending on the
selected fail-safe action. A change in the sig-
nal pressure acting on the diaphragm causes
the plug to move. The actuator size is deter-
mined 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.
Tip
We recommend the use of positioners with
integrated diagnostic firmware (see Chap-
ter 3.3) for valves used for on/off service.
The partial stroke test included in this soft-
EB 8015 EN

Design and principle of operation

ware helps prevent a shut-off valve normally
in its end position from seizing up or getting
jammed.
Fail-safe action
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
actuator stem downward and close the
valve. The valve opens when the signal
pressure is increased enough to over-
come the force exerted by the springs.
− Actuator stem retracts (FE)
When the signal pressure is reduced or
the air supply fails, the springs move the
actuator stem upwards and open the
valve. The valve closes when the signal
pressure is increased enough to over-
come the force exerted 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