3 Water Level Control
04.09.2016 Mk8 MM Expansion Features Installation and Set-Up Guide Page 67
3.9.4 Sudden Pressure Drop
Swell management uses the firing rate and boiler pressure to prevent intermitted shutdowns due to 1
st
low level alarm being activated during transitory conditions.
Please see section 3.4.1 for more information swell management.
The table below shows the expansion options for sudden pressure drop.
Expansion Option Description
24 Sudden pressure drop trigger rate
25 Sudden pressure drop control point increase
26 Sudden pressure drop reset offset
When there is a critical load demand, steam is drawn from the header rapidly. The boiler steam
pressure will then decrease, so the MM will increase its firing rate to meet the load demand.
A sudden pressure drop condition will be true, when the pressure drops by the value set in expansion
option 24 over a time of 3 seconds, to a pressure below the reset offset from the require pressure set in
expansion option 26. When a sudden pressure drop is detected, the control point is increase by the
percentage set in expansion option 25.
Without the sudden pressure drop function, the system would be see a 1
st
low water level alarm as the
feed water pump/servomotor would not react quick enough to maintain the water in the boiler.
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