Study of steam chest control valves in steam turbines.

摘要

Steam turbine control valves are the typical mechanism for regulation of flow into the main turbine itself. However, there has been a long history concerning the failure of the control valves. The failure that the valves experience all seems to be at the same area, which is failure between the valve stem and the top of the valve plug. It also has been theorized that the valve failure is due to fluid-flow induced vibration. This study investigates the valve failure and attempts to recreate the flow through a valve to obtain data points at various positions along the valve plug head as well as the valve seating. The main system studied is a quad-valve system, with the main complication occurring with the middle two valves during their lift action. Current fundamentals of flow theory around valves was considered and integrated with previous research concerning valve failure due to fluid-induced vibration. The actual problem concerning the current valves was then studied and the general causes investigated. Theoretical calculations based on basic theory of fluid-flow induced vibrations were done to obtain an initial theoretical view of the induced vibrations to design an actual experimental setup. Preliminary valve flow calculations were conducted to assist in the design of the experimental testing setup and to predict the possible data that is expected from the actual testing. The primary design concepts for the experimental setup include a single-valve, half-scaled design, with the use of a vacuum pump to induce the flow.