Inspection of Control Valve

Inspection and Maintenance of Control Valves

Inspection Before Starting Operation

Before starting operating of the control valve,  check & confirm the following to ensure all conditions are correct and secure.

• Confirm that the flow direction marked on the control valve conforms with the process fluid flow direction.
• Confirm that the bolts and nuts of the diaphragm are securely tightened.
• Confirm that bonnet clamp bolts are securely tightened.
• Confirm that the yoke clamp bolt is securely tightened.
• Confirm that the clamp bolts of any accessory devices (positioner, regu- lator valve, etc.) are securely tightened.
• Confirm that the air connection to the actuator is securely tightened and there is no air leak.
• Confirm that the bolts of the stem connector that connect the actuator stem to the valve stem are securely tightened.
• Confirm that the actuator stem and valve stem are not warped or show any other sign of defect.
• Confirm that the control valve smoothly operates within its full lift scale range.
• Confirm that the actuator spring is correctly compressed.
• Confirm that gland packing bolts are sufficiently 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.

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 fluid leak from the bonnet and flanges.
• Check that the yoke clamp bolt is not loose.
• Check that there is no air leak from the air piping of the actuator.
• Check that there are no loose bolts on the stem connector which connects the actuator stem to the valve stem.
• Check that the actuator stem and valve stem are not warped and show no sign of damage.
• Check that valve operation is smooth and valve lift is correct
• Check that the control valve does not generate any abnormal sound or vibration.
• Check that there is no leak from the gland packing section. If the control valve has a lubricator, periodically lubricate and tighten the gland packing section.
• If the Control valve has a manual handwheel, check that the pointer of the operation nut conforms with the AUTO position and that the hand- wheel is locked