3-3. Troubleshooting
Problems that might occur during operation are described in Table 3-2.
Take necessary measures such as replacing parts, depending on the circumstances
Table 3-2. Control valve problem causes and countermeasures
Phenomenon Cause Countermeasure
Unreliable valve operation
The valve hunts near the
fully closed position.
The valve capacity is too large.
•
Reduce the differential pressure between the
inlet and outlet of the valve.
•
Replace the valve trim with trim that has a
smaller Cv.
Reverse flow direction
•
Check that the flow direction indicated on
the valve is the same as the fluid direction. If
not, change the direction.
Fluctuation in supply air
pressure
Insufficient instrumentation air capacity
of the equipment
•
Increase the capacity of the compressor.
•
Install an additional dedicated compressor.
Failure of the air pressure regulator
•
Check the air pressure regulator.
Hunting of signal pressure The resistance or air volume of the con-
trol loop is not suitable.
•
Insert an air volume tank or restrictor into
the signal pressure line.
Failure of the controller
•
Check the controller.
The valve hunts even
though signals and supply
air pressure are stable.
Hunting of the positioner circuit
•
Check for wear of the positioner
•
Check the positioner and pilot valve
•
Reduce the sensitivity of the positioner
Fluctuation in axial thrust due to
changes in fluid pressure in pipes
•
Reduce the differential pressure between the
inlet and outlet of the valve.
•
Replace the actuator with one that has more
rigidity.
•
Add a positioner.
Valve vibration
The valve vibrates at any
travel.
Insufficient support for the piping
•
Support the inlet and outlet of the valve.
There is a source of vibration around
the valve.
•
Remove the source of vibration.
The guide is worn out.
•
Replace the guide bushing and/or the valve
plug.
Slow valve stroke
Valve stroke is slow in
both opening and closing
directions.
The valve plug guide, the fluid retaining
part of the bonnet, etc., is clogged with
slurry.
•
Disassemble and clean.
•
Install a steam jacket on the valve body.
The gland packing is hardened.
•
Replace the gland packing or the grease.
3-2
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