Samson 4765 - Setting for Actuator with Fail-Safe Action Stem Extends; Setting for Actuator Version Stem Retracts

22 EB 8359-1 EN
Operating the positioner
6.3.2 Setting for actuator with
fail-safe action “stem
extends”
To ensure that the total closing force of the
actuator acts on the valve, proceed as fol-
lows:
Î With direct operating direction <<:
adjust starting point to 0.23bar (slightly
raised).
Î With reverse operating direction <>:
adjust starting point to 0.97bar (slightly
lowered).
Starting point (zero) e.g. 0.23bar
1. Turn the zero adjustment screw (4) until
the plug stem just starts to move out of its
resting position (observe travel indica-
tor).
2. Reduce the input signal to 0bar and
slowly increase it again. Check whether
the plug stem starts to move at exactly
0.23bar and correct, if necessary.
Upper range value (span) e.g. 1bar
3. Once the starting point has been set, in-
crease the input signal. At exactly 1bar,
the plug stem must stand still, having
moved through 100% travel (watch the
travel indicator at the valve).
If the upper range value is incorrect,
move the pin (2) as follows to correct it:
4. Move towards
Lever end à To increase the travel
Fulcrum à To reduce the travel
After correcting the input signal, re-ad-
just zero. Then check the upper range
value again.
Repeat the correction procedure until both
values are correct.
If a pressure gauge is available, check
whether the actuator is completely vented at
an input signal of exactly 0.2bar (operating
direction <<) or exactly 1.0bar (operating
direction <>).
6.3.3 Setting for actuator ver-
sion “stem retracts”
When using an actuator with fail-safe action
"actuator stem retracts", the diaphragm
chamber must be pressurized with a signal
pressure that is high enough to tightly close
the valve against the upstream pressure in
the plant.
Î Operating direction <<: Upper range
value of reference variable 1bar
Î Operating direction <>: Lower range val-
ue of reference variable 0.2bar
The required signal pressure is either
indicated on the positioner label or it can be
roughly calculated as described in
section5.4.2.
Starting point (zero) e.g. 1bar
1. Adjust the input signal to 1bar at the
pressure adjuster.
Turn the zero adjustment screw (4) until
the valve just starts to move from its ini-
tial position.
2. Increase the input signal and slowly re-
duce it again to 1bar. Check whether