10 Water Level Control
Mk8 MM Manual Page | 200
10.10.4 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 3.5.1 for more information on swell management.
The table below shows the expansion options for sudden pressure drop.
Sudden pressure drop trigger rate
Sudden pressure drop control point increase
Sudden pressure drop reset offset
When there is a sudden steam demand, steam is drawn from the header rapidly. The boiler steam pressure
will decrease quickly, 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 will trigger a 1
st
low water level alarm as the feed
water pump/servomotor would not react quick enough to maintain the water level in the boiler.