Design And Principle Of Operation - Samson 3241-7 Mounting And Operating Instructions

Design and principle of operation

1 Design and principle of opera-
tion
The Type 3241-1 and Type 3241-7 Pneu-
matic Control Valves consist of a Type 3241
single-seated Globe Valve and either a
Type 3271 or Type 3277 Pneumatic Actua-
tor.
Thanks to the modular design, the actuators
can be exchanged, and the standard version
of the valve can be supplemented to form a
version with extension bonnet or metal bel-
lows seal.
In the micro-flow valve version, a micro-trim
element is installed in the valve body instead
of the usual seat-plug assembly.
The process medium flows through the valve
in the direction indicated by the arrow. The
position of the plug (3) determines the flow
through the valve seat (2). The position of
the plug (3) is changed by the signal pres-
sure acting on the diaphragm of the actua-
tor (bench range). Plug (3) and actuator
stem (8.1) are connected by the stem con-
nector (7) and sealed by the spring-loaded
ring packing (4.2).
Fail-safe position
The control valve provides two different
fail-safe positions depending on the ar-
rangement of the springs in the actuator:
Actuator stem extends
When the signal pressure is reduced or the
power supply or signal fails, the springs
move the actuator stem downwards and
close the valve.
When the signal pressure increases again,
the valve opens acting against the force of
the springs.
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EB 8015 EN
Actuator stem retracts
When the signal pressure is reduced or the
power supply or signal fails, the springs
move the actuator stem upwards and open
the valve.
When the signal pressure increases again,
the valve closes acting against the force of
the springs.
2 Assembling valve and actuator
The basic pneumatic actuator can be re-
placed by an electric actuator or a pneu-
matic actuator with additional handwheel.
A pneumatic actuator (with or without
handwheel) can be exchanged for another
pneumatic actuator in a different size.
If, in the valve-actuator assembly, the travel
range of the actuator is larger than the
travel range of the control valve, the actua-
tor springs are preloaded by the manufac-
turer so that the travels match.
2.1 2.1 Assembly and adjustment
If the valve and actuator have not been
pre-assembled by the manufacturer, or if the
actuator of a valve is to be replaced by an
actuator of another type or another size,
proceed as described below.
1. Unscrew the lock nut (6.2) and stem con-
nector nut (6.1).
Firmly press the plug together with the
plug stem into the seat ring. Make sure
the large V-shaped port of the V-port
plug faces towards the valve outlet.
Thread the stem connector nut and lock
nut downwards.