Analysis and research on the vibration characteristics of the pressure maintaining valve of the deaerator based on structural dynamics

Abstract The deaerator pressure-maintaining valve is a critical control component in a power plant thermal system, and its operational stability directly affects unit safety and economic performance. To investigate abnormal vibration induced by steam flow and unsteady pressure loading, a three-dimensional finite-element model of the valve was established. After geometric simplification, material-property assignment, and mesh-independence verification, a one-way sequential fluid-structure interaction approach was used to map the unsteady pressure distribution obtained from transient flow simulations onto the wetted structural surfaces. Prestressed modal analyses were performed at valve openings of 14 and 28 %, while harmonic response and transient structural dynamic analyses were conducted at the representative opening of 14 %. The results show that the first 10 natural frequencies under both opening conditions fall within 4.79–21.31 Hz, with the first six not exceeding 10.21 Hz, indicating pronounced low-frequency clustering. The spring assembly and guiding structure exhibit relatively large deformation in most normalized mode shapes, demonstrating high local flexibility and dynamic sensitivity. Harmonic response results indicate that the response amplitudes in the 87.5–100 Hz range are relatively high within the investigated frequency band, with larger deformation concentrated mainly in the spring assembly and guiding structure. Transient analysis further shows that the directional displacement at the valve-stem monitoring point exhibits sustained oscillation under time-varying fluid loading, ranging approximately from −0.2 to 0.2 mm. This suggests that the valve stem and spring load-transfer assembly may experience repeated cyclic loading during long-term operation and therefore face a potential fatigue risk. Accordingly, vibration-mitigation measures, including local flow-passage improvement, stiffness enhancement of critical connections, and appropriate damping configuration, are proposed to improve the valve’s dynamic stability and operational reliability. The findings provide a reference for the vibration-resistant design and abnormal-vibration diagnosis of similar steam control valves.