Experimental study of steam turbine control valves

Abstract

Because of the converging-diverging con guration of the valve passage, venturi valves have been widely used in large turbines to regulate inlet ow as turbine governing valves for about half a century. From the 1960s, a number of valve failure incidents have been reported. Improvement to current designs was strongly demanded but, owing to the complicated nature of the uid-structure interaction mechanisms, the basic mechanism causing valve failure is still far from being fully understood. Experimental investigations on a half-scale valve were performed here. The study con rmed that asymmetric unstable ow is the root cause of valve problems, such as noise, vibration and failure.

Analysis of flow-induced instability in a redesigned steam control valve

“…Compared to the results of the previous valve design studied [3], and [4], the flow rates through this valve are similar. The greatest variance occurs at high pressure ratio and low opening ratio where the old valve flows up to 20% more mass.…”

“…The proposed new designs were found to be better in terms of reduced excitations of valve vibration, especially in large pressure ratio conditions. The work presented here is a continuation of the work of Zhang and Engeda [3] and Zhang et al [4]. The new valve, shown in Fig.…”

“…The previous valve, studied in Refs. [3] and [4], showed greater tendency towards asymmetry in the seat and inner ring, especially at low PR. However, the outer ring was showed less symmetry in the new design compared to the old design.…”

“…It has been reported that the flow pattern around the valve is a transonic and separated jet, and as a result, mass flow fluctuations with large pressure fluctuation occurs as described by Widel [1], Araki et al [2] and Zhang and Engeda [3], Zhang et al [4], Morita et al [5], Morita et al [6], Yonezawa et al [7] and Yonezawa et al [8]. As a result steam turbine control valves are known to be a source of noise and vibration.…”

“…Recently a series of investigations carried out by Zhang and Engeda [3] and Zhang et al [4], including experimental, analytical and numerical studies on turbine governor valve to clarify the fluid/ plug interaction mechanism. They confirmed that asymmetric unstable flow was the root cause of valve issues due to the resulting large amplitude unsteady forces, moments and torque.…”