Azbil HLS Series - Chapter 12. Troubleshooting

12-1
Chapter 12. Troubleshooting
This chapter covers the symptoms, causes and remedies of most probable types of troubles.
Parts may be required to be replaced depending on the type of trouble. For further troubles,
please ask an Azbil Corp. agent for repair.
Table 1-1. Troubleshooting
Symptom Cause and Remedy
Unstable valve operation
• Valve position hunting
occurs when almost
fully closed.
• Cv value is too large. Reduce Cv value.
• For a single scat Valve, the valve is Installed in the reverse
flow direction.
• Air supply pressure is
unstable.
• Large air consuming equipment is hooked up to the same air
supplyline. Check that the air supply capacity piping capacity
and restriction capacity are appropriate.
• Supply air pressure regulator is inadequate or not operating
properly.
• Signal pressure is
unstable.
• Controller is not properly tuned. Property tune the controller
(properly set the proportional band and other parameters).
• Check that the controller output does not change abnormally.
• Valve position
hunting occurs even
when signal pressure
isstable.
• Hunting of output of positioner itself. Check and repair or
replace thepositioner.
• Being affected by pressure change of process fluid as power of
Vibration of valve
• Valve vibrates
(generate noise) at any
position of valve plug.
• Piping is vibrating. Securely fix the piping.
• Check for other sources of vibration. Worn valve plug or
guides. Check the parts and replace them as required.
• Valve vibrates
(generate noise)only
when valve plug is set
at acertain position.
• Check for change in process fluid flow conditions (change in
restriction orifice, Cv value, etc.)
• Check for change in plug configuration (change in flow
control characteristics.)
Sluggish valve operation
or inoperative Valve
• Air leak from piping
• Air leak from actuator
• Foreign matter entrapped in guide section of valve plug.
• Aged and hardened gland packing, causing increased
hysteresis
• Malfunctioning positioner (Check the positioner by
operating it directlyon an air supply known to be operating
normally.)
Fluid leak from gland
section
• Check for loose packing flange.
• Check for insufficient grease.
• Check for damaged valve shaft.
Liquid leak from gasket
section
• Check for Ioose nuts of bonnet.
• Check for defective gasket (deformed or damaged).