Effect of Seat Shape on Control Valve for Large Steam Turbines

Among various valves that control the steam flow to the turbine, the control valve is certainly the most significant. The steam flow rate is determined by the area formed by the stem disk and the seat of the control valve. While the ideal control valve linearly controls the steam mass flow rate with its stem lift, the real control valve has various flow characteristic curves pursuant to the stem lift. Thus, flow characteristic curves are needed to precisely design the control valves manufactured for the operating conditions of power plants. VELO (Valve Engineered Layout Operation) experimentally determines the characteristic curves for the flow control in the steam power plants. The Widows' Creek type control valve is the reference model and air is selected as the working fluid. Previous experimental flow coefficients for the high opening of the control valve and the region of high pressure ratios were found to be lower than those of the reference but essentially identical in the low opening and the region of low pressure ratios. VELO is newly performed to particularly check on any change in the flow coefficient depending on the length of a pipe section attached to the valve exit. According to the VELO test results, however, the flow coefficient in the region mentioned does not change and a difference is recently found in terms of modelling the valve and the seat. It is thus revealed that the seat of the scaled down valve in VELO is different from reference. In order to make sure whether the seat shape will increase the flow coefficients or not, the seat of the valve in VELO is remodeled and analyzed by utilizing the commercial computational fluid dynamics