How Does a Low-Water Cutoff on a Steam Boiler Work?

Definition

• If the water level in a steam boiler drops too low, the water will turn into steam too quickly and the boiler will be left with a large amount of thermal energy and nothing to absorb it except the tank and surrounding components. The result is severe damage to the boiler, burner and nearby systems, with the possibility of a fire hazard. The low-water cutoff system detects when water is reaching low levels that may cause this problem and shuts the system off before any issues can occur.

Probe

• The primary sensor of the cutoff unit is a probe that extends into the tank. This probe operates using a very simple process: As long as it is covered with water, it completes the circuit to the cutoff control panel. If water falls below this point, the circuit is broken. The probe cannot detect why water may have fallen to this point, only that the boiler is in danger.

Signal

• When the circuit is broken, the cutoff control panel sends a signal to the burner and power systems of the boiler. This signal overrides current operations and shuts all the systems down completely, preventing the boiler from producing heat that might damage it. Some boilers have both primary and secondary cutoff units that protect different parts of the system, such as the tank and the pump.

Features

• Extra features may be included in the water cutoff device. Some may have test buttons that automatically test the wiring to ensure all connections are properly made, showing the results with a series of LED lights. These lights can also double as a symptom checker that may indicate if the probe is dirty or if the water level has actually gone down.