EB 8015 EN 8-1
Malfunctions
8 Malfunctions
Read hazard statements, warnings and caution notes in the 'Safety instructions and mea-
sures' chapter.
8.1 Troubleshooting
Malfunction Possible reasons Recommended action
Actuator and plug stem
does not move on
demand.
Actuator is blocked. Put the control valve out of operation (see the
'Decommissioning' chapter) and remove the
blockage.
WARNING! A blocked actuator or plug stem (e.g.
due to seizing up after remaining in the same
position for a long time) can suddenly start to
move uncontrollably. Injury to hands or ngers is
possible if they are inserted into the actuator or
valve.
Before trying to unblock the actuator or plug stem,
disconnect and lock the pneumatic air supply as
well as the control signal. Before unblocking the
actuator, release any stored energy in the actuator
(e.g. spring compression). See associated actuator
documentation.
Diaphragm in the
actuator defective
See associated actuator documentation.
Signal pressure too low Check the signal pressure.
Check the signal pressure line for leakage.
Jolting movement of the
actuator and plug stem
Version with adjustable
packing
1)
: packing
tightened too far
Tighten the packing correctly (see section
'Adjusting the packing' in the 'Installation' chapter
> 'Testing the installed valve').
Actuator and plug stem
does not stroke through
the full range.
Signal pressure too low Check the signal pressure.
Check the signal pressure line for leakage.
Travel stop active See associated actuator documentation.
Incorrect setting of valve
accessories
Check the settings of the valve accessories.
Increased ow through
closed valve (seat
leakage)
Dirt or other foreign
particles deposited
between the seat and
plug.
Shut off the section of the pipeline and ush the
valve.
Valve trim, particularly
with soft seat, is worn.
Replace seat and plug (see the 'Servicing' chapter)
or contact our after-sales service.
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