Managing Low Water In A Steam Boiler

| Edward McKellar

A low water situation in a boiler is a potentially catastrophic situation. Data consistently supports that the majority of boiler accidents are a result of varying low water situations. When a low water condition begins in a boiler it can begin damaging the boiler even before there is an immediately noticeable problem. If the condition persists, the risk of serious damage and danger exists. Low water conditions occur when a boiler is insufficiently replacing the water to meet the evaporation rate and the control doesn’t respond accordingly. 

Prevent Low Water Conditions In Boiler

A top priority inside a boiler room is to control the water level inside of these pressure vessels. When steam is being generated there is an obvious loss of water and it’s imperative that the makeup water is replaced accurately. An industry-standard control for steam boilers is the McDonnell Miller. There are various models of these controls to meet different applications such as modulating feed systems, on/off operation, as well as for higher and lower pressure ranges

Picture of steam boiler valves.

Many times these controls are dual functioning, meaning that they serve as a low-water fuel cut-out, as well as a level control. Under normal operating conditions, as steam is being generated the control sends a signal to close the circuit for the feed pumps. Pumps will energize and bring the water level back up to the normal operating level as indicated by the boiler manufacturer. Once this level is reached the pump circuit will close and the boiler will operate as normal. Should the water level continue to drop, the float will fall accordingly and shut the burner off. 

Understanding the general operations of the low-water cutoff helps to understand the necessity of performing routine maintenance and checks on these controls. Accumulations of scale inside the body of the low water cutoff, along with compromised floats will give a false level indication. These scenarios can lead to trouble quickly inside a steam boiler

Picture of steam boiler pump

Best Practices To Ensure Low Water Cutoffs Work

The best practices for ensuring your low water cutoffs are reliable are through functions checks and blowdowns. During a daily blowdown procedure, the general function can be verified. With the burner on and in a low-fire situation, the blowdown valves are opened and as the water level falls, the burner should cut out. Pumps should have engaged and upon closing your blowdown valves the water level should return and the burner should get a call for a heat signal to restart its sequence. Other performance checks like the slow low water test or evaporation test method can further analyze if there may be a problem with the low water cutoff. Because of the critical nature of this control its best to ensure that these tests are performed by qualified individuals

Picture of blue steam boiler.

What Is The Purpose Of Water In A Boiler?

The water inside the boiler is the primary means for protecting the metal surfaces from thermal damage. A boiler that is being starved of water can quickly produce shocking effects on the tubes, tube sheets, and other metal surfaces. If the low water continues the damage and severity continue to increase. Data repeatedly supports that most boiler-related accidents are from some varying form of a low-water condition. Many organizations replace the low water cutoff at set intervals regardless of its functionality. This is an extra measure taken to ensure that this primary safety is functioning as expected. 

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