Two shift Feed water control valves
Two shift operation power plants
Feed water control valves are important components of a steam installation, as they control the supply of feed water to the boiler. The physical demands on this valve are high so that, with a carefully selected feed water pump with minimal pressure drop at full load, no energy is wasted.
However, when the boiler is starting from cold the requirements from the valve are totally different. As the valve is required to control a small mass flow with a high delta P, the required rangeability can no longer be realised by one valve alone. Potential cavitation will easily damage the valve.
Generally the solution is found in the installation of a second control valve, the startup or the so called 30% valve. Installed parallel with the main feed water control valve, this valve can handle
Small mass flows at high pressure drops, and therefore the
change from the start up valve to the main valve is not an easy
but can only be achieved with good craftsmanship.