10 Water Level Control
Mk8 MM Manual Page | 198
10.10 Water Level Control Functions
This section describes the additional functions used to accurately control the water level.
10.10.1 Pre-Alarms
In addition to the water level alarms for high water, 1
st
low and 2
nd
low, pre-alarms can also be set which
include pre-high and pre-1
st
low.
The table below shows the expansion options for pre-alarms.
Pre-high alarm percentage
Pre-first-low alarm percentage
The pre-high level is set as a percentage between the control point and high water level, with the control
point representing 0% and the high water level representing 100%. If the water exceeds this pre-high level, a
warning will be triggered and the burner will continue to fire.
The pre-1
st
low level is set as a percentage between the control point and 1
st
low level, with the control point
representing 0% and the 1
st
low level representing 100%. If the water falls below this pre-1
st
low level, a
warning will be triggered and the burner will continue to fire.
10.10.2 Pump Bypass
The pump bypass operation prevents the pump pushing water against a closed feed water valve. The MM
terminal used is TB - pump bypass contactor.
The table below shows the expansion options for pump bypass.
The pump can be bypassed at a percentage set in expansion option 18, above or below the switch point.
The switch point is set as percentage of the feed water valve open position set in expansion option 16.
For pump bypass on above switch point, the pump bypass will turn on at a percentage above the valve open
range set as a switch point, and it will turn off at a percentage below the switch point set as the hysteresis
from the switch point.
For pump bypass on below switch point, the pump bypass will turn on at a percentage below the valve open
range set as a switch point, and it will turn off at percentage above the switch point, set as the hysteresis
from the switch point.
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