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Observing end position
Positioner-valve linkage
Working range
Friction
Actuator springs
Inner (seat) leakage
External leakage
PST/FST
EB 8389S EN
Possible reasons
− Course of end position
monotonically increasing/
decreasing.
− Course of end position al-
ternates.
− No optimal travel trans-
mission.
− The mechanical link is
loose.
− The working range is limit-
ed.
− The working range is
mainly close to the
CLOSED/max. OPEN po-
sition.
− The working range is
mainly in the CLOSED/
max. OPEN position.
− The friction is much high-
er/lower over the entire
working range.
− The friction is much high-
er/lower over a section.
− The spring stiffness is re-
duced (spring failure).
− The spring pre-loading is
reduced.
− The actuator springs are
working at full capacity.
Seat leakage exists.
External leakage may possi-
bly exist or is to be expected
soon.
External leakage is perhaps
soon expected.
The partial stroke test or the
full stroke test has not been
completed successfully.
Recommended action
Check seat and plug.
Check attachment.
Rethink the working range.
Check the valve's packing.
Check actuator springs.
Check seat and plug.
Check the valve's packing.
Check test cancelation con-
ditions. See section 4.4
and section 4.5.
Appendix
Status clas-
sification
Single reset
•
•
[
]
Sec. 3.8.2
u
•
•
[
]
Sec. 3.4.2
u
•
•
[
]
Sec. 3.3.2
u
•
•
[
]
Sec. 3.7.2
u
Sec. 4.2.2
u
•
•
[
]
Sec. 3.6.2
u
Sec. 4.1.2
u
•
•
[
]
Sec. 3.4.2
u
•
•
[
]
Sec. 3.5.2
u
•
Sec. 3.7.2
u
•
•
[
]
Sec. 4.4.4
u
Sec. 3.5.2
u
95
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