VDC, VAC, VST, VAA - Diaphragm Control Valve 3-1
Chapter 3 : Inspection and Maintenance of
Control Valves
For the inspection and maintenance of a control valve, also refer Chapter 4.
“Adjustment.”
3-1 : Inspection Before Starting Operation.
Before starting operating of the control valve, check & conrm the following to
ensure all conditions are correct and secure.
• Conrm that the ow direction marked on the control valve conforms with the
process uid ow direction.
• Conrm that the bolts and nuts of the diaphragm are securely tightened.
• Conrm that bonnet clamp bolts are securely tightened.
• Conrm that the yoke clamp bolt is securely tightened.
• Conrm that the clamp bolts of any accessory devices (positioner, regulator
valve, etc.) are securely tightened.
• Conrm that the air connection to the actuator is securely tightened and there is
no air leak.
• Conrm that the bolts of the stem connector that connect the actuator stem to the
valve stem are securely tightened.
• Conrm that the actuator stem and valve stem are not warped or show any other
sign of defect.
• Conrm that the control valve smoothly operates within its full lift scale range.
• Conrm that the actuator spring is correctly compressed.
• Conrm that gland packing bolts are suciently tightened.
• If the control valve employs asbestos packing, it is recommended to lubricate it
with the lubricator.
• If the control valve has a manual handwheel, check that the pointer of the
operation nut is at AUTO position and the handwheel is locked.
3-2 : Periodical Inspection and Maintenance
Periodically inspect and perform maintenance service to the control valve for the
following:
• Check that there is no air leak from between the diaphragm case and diaphragm.
• Check that there is no process uid leak from the bonnet and anges.
• Check that the yoke clamp bolt is not loose.
• Check that there is no air leak from the air piping of the actuator.
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