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8.5 Adjustment
The only adjustment that can be made on the posi-
tioner is a zero adjustment. The zero adjusting screw
is located under the positioner’s top cover. To make
this adjustment, set the instrument air pressure to
the midpoint of its span, and turn the zero adjust-
ment until the valve is at the mid-point of its stroke.
Refer to Table #2 for stroke information. Recheck the
setting accuracy by changing instrument air pressure
to the maximum/minimum point to obtain full
open/closed valve position.
In some cases, valve shut-off or opening may be
required at a specific instrument pressure. To zero
the positioner at this point, set the instrument signal
at the specific pressure and turn the zero adjustment
screw until the valve reaches the required position. A
slight change of the instrument pressure should start
to move the valve. The valve stroke for a given span
may also be suppressed or shifted to the desired
range by means of the zero adjusting screw.
8.6 Maintenance
A clean, oil and moisture free air supply will reduce
maintenance problems. The supply air filter should
be blown down on a routine basis. The filter element
should be examined periodically and replaced if nec-
essary. No lubrication is required on the valve posi-
tioner. The system should be shut down or the valve
isolated from the system before service or removal of
the positioner is accomplished.
For additional maintenance activities, refer to the
Manufacturer’s service manual.