Two Shift Drain Valves
Drain valves are amongst the most complicated valves used in a power station. The valves have to be designed for the primary pressure and temperature conditions, in this case 179.3 barg and 568 dgr C.
However in practice the working conditions of these valves can be totally different from the design conditions. When the station is starting up or shutting down, the collected condensate needs to be discharged during start up through the drain control valve into the drain vessel. Both pressures and temperatures can fluctuate across a wide range during this process.
The correct performance of the drain system is imperative on a station where the system is expected to perform multiple stop-start cycles as commonly seen when stations start to dual shift, as opposed to the drain valves on a base load station which are designed to operate only once or twice a year.