Samson Type 3766 Mounting And Operating Instructions - "actuator Stem Retracts"
If the upper range value is incorrect, turn the
span
adjuster (travel). Four turns correspond
to a travel change of 10 % in standard oper-
ation. In split-range operation, this value is
reduced by half.
Turn the adjuster clockwise to reduce the
travel and counterclockwise to increase it.
2. After correction has been completed,
shut off the input signal and slowly in-
crease it again. Check the starting point
and the upper range value. Repeat the
correction procedure until both values
are correct.
4.1.3 Settings for actuator:
"Actuator stem retracts"
NOTICE
When using an actuator with fail-safe ac-
tion"Actuator stem retracts", the diaphragm
chamber must be pressurized with a signal
pressure that suffices to tightly close the
valve even when an upstream pressure is
applied in the plant. This applies to an up-
per range value of the reference variable
(1 bar) and operating direction >> as well
as a lower range value of the reference vari-
able (0.2 bar) and operating direction <>.
The required signal pressure is either indi-
cated on the positioner label or can be
roughly calculated as described in section
3.1.2.
Starting point (e.g. 1 bar)
1. Use the pressure adjuster to set the input
signal to 1 bar.
2. Turn the zero adjuster (6.2) until the
valve just starts to move from its initial
position.
3. Increase the input signal and slowly re-
duce it to 1 bar again. Check whether
the valve start to move at exactly 1 bar.
4. Correct any deviation on the zero
adjuster (6.2). Turning the adjuster
counterclockwise causes the valve to
move from its end position earlier; turn-
ing clockwise causes the valve to move
from its end position later.
Upper range value (e.g. 0.2 bar)
1. Once the starting point has been set, ad-
just the control signal to 0.2 bar using
the pressure adjuster. At exactly 0.2 bar,
the plug stem must stand still, having
passed through 100 % travel (watch the
travel indicator at the valve).
2. If the upper range value is incorrect, turn
the span adjuster (travel). Four turns cor-
respond to a travel change of 10 % in
standard operation. In split-range oper-
ation, this value is reduced by half.
Turn the adjuster clockwise to reduce the
travel and counterclockwise to increase
it.
3. After correction has been completed, re-
set the control signal to 1 bar.
4. Turn the zero adjuster (6.2) again until
the pressure gauge indicates the re-
quired signal pressure (see sec-
tion 3.1.2).
34
EB 8355-1 EN
Operation