The function of high and low level alarms. Low-level alarms will draw attention to low boiler water level and, if required, shut down the boiler. High-level alarms protect plant and processes.
Where boilers are operated without constant supervision (which includes the majority of industrial boilers) low water level alarms are required to shut down the boiler in the event of a lack of water in the boiler. Low level may be caused by:
The regulations covering boilers have built up over the years in response to boiler explosions, damage and loss of life. Whilst boiler explosions are now very rare, damage to boilers which is attributable to low water level still occurs.
The effect of low water level in a boiler is that the heated tubes or the furnace tube(s) become uncovered and are no longer cooled by the boiler water. The metal temperature rapidly increases, its strength is reduced and collapse or rupture follows.
Low water alarm
The action of the low water level alarms under UK regulations is as follows:
The rules and regulations covering boiler operation, and the controls required, will vary from country to country, although demands for higher levels of safety, plus a desire to run steam boilers without the permanent presence of a boiler attendant, are tending to drive the regulations in the same direction.
The action of low water alarms outlined above, relates to the regulations governing unattended steam boiler plant in the UK. However, they are similar to the rules which are applied in many European countries and further afield.
High water alarm
With the exception of one or two operating standards, the risks from a water level too high are treated very lightly, if not ignored altogether.
The dangers of an excessively high water level in a steam boiler include:
As can be seen, the dangers of an excessively high water level are too serious to ignore, and deserve equal consideration to that given to low water level conditions.
A high water condition could:
The action to be taken largely depends on the individual plant requirements.