6
EB 8026 EN
Design and principle of operation
2
Design and principle of oper
-
ation
The Type 3244-1 and Type 3244-7 Pneu
-
matic Control Valves consist of the
Type 3244 Three-way Valve and either a
Type 3271 or Type 3277 Pneumatic Actua
-
tor. The modular design allows the actuators
to be exchanged and an insulating section
or metal bellows to be fitted to the standard
valve version.
Depending on the plug version, the three-
way valve can be used either as a mixing or
diverting valve (in DN 15 to 25, the plugs
are identical).
In mixing valves, the process media to be
mixed enter at valve ports
A
and
B
. The
combined flow exits the valve at port
AB
.
In diverting valves, the process medium en-
ters at the valve port
AB
and the partial
flows exit at ports
A
and
B
.
The flow rate from ports
A
or
B
to
AB
and
vice versa depends on the cross-sectional ar-
ea of flow between the seat (2.1, 2.2) and
plug (3) and, as a result, on the position of
the plug stem (6).
The plug (3) is moved by a change in signal
pressure acting on the diaphragm of the ac-
tuator.
The plug stem (6) and actuator stem (8.1)
are connected by the stem connector (7) and
sealed by a spring-loaded PTFE ring packing
(4.2).
Fail-safe position
Depending on how the compression springs
are arranged in the actuator, the valve has
two different fail-safe positions:
Actuator stem extends
When the pressure is relieved or the supply
air fails, the springs cause port
B
(mixing
valves) or port
A
(diverting valves) to close.
The valve ports
B
or
A
are opened against
the force of the springs when the signal pres-
sure increases.
Actuator stem retracts
When the pressure is relieved or the supply
air fails, the springs cause port
B
(mixing
valves) or port
A
(diverting valves) to open.
The valve ports
B
or
A
are closed against the
force of the springs when the signal pressure
increases.