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3 Design and principle of oper-
ation
The single-seated Type 3281 Globe Valve
acts as a steam conditioner and is fitted with
a flow divider ST 3. The Type 3281
Steam-conditioning Valve is preferably com-
bined 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), flow divider (62) 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
(A26/27) and is sealed by a spring-loaded
V-ring packing (15). Alternatively, an adjust-
able high-temperature packing can be used.
The springs in the pneumatic actuator are lo-
cated either above or below the diaphragm
(A4) depending on the selected fail-safe ac-
tion (see section 3.1). A change in the signal
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 and the pres-
sure p
as well.
2
The cooling water is fed to the flow divider
(62) through the connecting pipe on the bon-
EB 8251 EN
Design and principle of operation
net (2) and holes in the clamping element
(63). After flowing through the cross-section-
al area between seat and plug, the steam
flow reaches its maximum velocity and
comes into contact with the cooling water at
the inner wall of the flow divider. The steam
flow and the entrained water are mixed in
the narrow wire mesh of the flow divider. At
the same time, the steam velocity is reduced,
releasing some of its heat to the water across
the large surface of the wire mesh coil,
which causes it to evaporate quickly. The
steam/water mixture leaves the flow divider
as a fine mist with a high steam content.
Evaporation is completed a short distance
downstream of the steam conditioning valve.
The water atomization described is ensured
over the whole load range since the steam
velocity at the throttling point is independent
of the flow rate.
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-
3-1
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