The control valve is the weakest part of the air inlet system of the steam turbine

and its vibration problem seriously affects the economy and safety of the unit operation. In a power plant

the vibration of control valve stem system has caused the loose of valve stem connectors

the damage of screw thread and shut down of control valve for several times. In order to maintain the unit operation

the valve stem and the connector have been welded. However

the vibration problem of the high-pressure control valve still cannot be solved. In order to study the root cause of the vibration of valve stem system

the vibration of valve stem in the lateral and axial direction are tested by a laser vibrometer. A modal analysis of valve stem system is performed. The results show that

the vibration of the valve stem system of the high-pressure control valve is caused by the resonance of valve stem system

which is caused by valve disc knocking on the valve stem due to the insufficient load of valve disc. The vibration of the valve stem system is suppressed effectively by increasing the load of valve disc.