Your main propulsion boilers are equipped with a two element feed water regulating control system. While on watch, you are required to respond to a 'slow' bell from full sea speed. Under these conditions the automatic feed water regulator will have __________.
• two-element feedwater control: what two variables does it sense and compare? • behavior of steam drum level during rapid load changes (swell vs. shrink) • how a sudden reduction in steam demand affects steam flow, drum pressure, and apparent water level
• When you go from full sea speed to a slow bell, does steam flow demand increase or decrease? How does that affect drum pressure and bubble content in the water? • In a shrink condition, does the indicated drum level move up or down? In a swell condition, does it move up or down? • Ask yourself whether the controller is seeing a higher or lower level and a higher or lower steam flow signal, and how a two-element system reacts to those combined signals.
• Clarify the difference between swell (apparent level rise) and shrink (apparent level drop) in a steam drum. • Confirm what the two elements are in a two-element feedwater regulator (typically drum level and steam flow). • Check which option correctly links the direction of level change (swell or shrink) with the expected controller action on the feedwater valve (open more vs. close down).
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