A boiler works under pressure, and it is not possible to see what is happening inside of it. The terms "wet steam" and "carry-over" are everyday idioms in the steam industry, yet very few people have ever seen these phenomena and the actual water movement inside a boiler has remained highly speculative.
However, actual boiler operations have since been recorded on videotape and it definitely illustrates the effects of steam quality vs. boiler efficiency during different boiler and steam systems demands. As the video shows, there are four different operating situations that affect steam quality: