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Three possible failure scenarios will be presented. The first scenario will introduce the occurrences leading to the first possible problem, and the following two scenarios will explain subsequent possible problems and actions that prevent damage to the unit.
Two pumps exist for moving water from the surge tank (right) to the DA tank (left), but under normal circumstances only one is running. If that running pump fails, the unit's first alarm system will try to turn on the other pump.
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Transfer pump #1 pumps water from the surge tank into the DA tank. Transfer pump #2 is currently off. In a situation where transfer pump #1 could not keep up with demand for feed water, both transfer pumps will run.
The boiler feed pump attached to the deaerator unit is constantly pumping water from the DA tank.
If for some reason transfer pump #1 failed in its operation, water in the DA tank would begin to fall.
When the water level in the DA tank drops enough, the float controlling the standby transfer pump is energized.
The standby transfer pump float signals transfer pump #2 to turn on and begin pumping water from the surge tank. The flow to the DA tank is now resumed and the water level returns to normal.
On extremely rare occasion that both transfer pumps suffer failure, the unit's second to last alarm system will trigger an audible alarm. The audible alarm notifies nearby personnel to care for it.
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If for some reason both transfer pump #1 and transfer pump #2 failed in their operation, water in the DA tank would begin to fall.
As shown earlier, the standby transfer pump float activates, however the water level inside the DA tank continues to fall because neither transfer pump is working. When the water level drops enough, it will trip the low water alarm.
When the low water alarm is triggered, it signals the electrical panel to turn on its alarm light and simultaneously activate the alarm bell.
At this point, the best case scenario would have personnel hearing the alarm bell and manually turning off the unit for technical service.
In the event that no personnel come to care for the unit and in order to prevent damage to itself, the unit's final system will trigger to shut off all pumping operation.
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Having triggered the alarm bell and failed to alert any personnel of dangerously low water level, the water level in the DA tank continues to fall until it triggers the final float switch.
When the water drops to lowest possible level it triggers the low water cut-off.
In order to prevent possible damage to unit, the low water cut-off signals to turn off the boiler feed pump preventing any further pumping operation.
The unit will permanently remain off until it can be serviced and restarted.