Three-Element Control in Boiler Drum Level

A typical scheme uses 3 float switches (or other liquid level sensors). Normally the middle one starts the feed water pump (or opens valve), and the upper one stops the pump (or closes the valve). If anything fails in the water supply and the level drops to the lower float switch, the boiler ignition shuts off. This is a critical safety item.

To simulate this you need some idea of how fast the boiler boils the water, and how fast the pump (or valve) replenishes it, and the dimensions of the upper drum. Then you can calculate how the water level goes up and down in it. This will give you the proportions of pump on/off time, and can be used to create graphic displays.

In addition to the above, remember that the boiler will blow down its contents every so often so as to eject some settled solids and reduce its dissolved solids, and the quantities and times will need to be considered in any mathematical modelling of this unit that needs to take place.