What is termed when there is a short-term decrease in drum water level due to a change in firing rate?

The term "shrink" refers to the short-term decrease in drum water level that occurs when there is a change in the firing rate of a boiler. This phenomenon can happen when the energy input to the boiler increases or decreases suddenly, affecting the water level in the steam drum.

When the firing rate decreases, less heat is being generated, which can lead to a temporary drop in the water level as the system adjusts to the new conditions. During this adjustment, the water may momentarily "shrink" in level until the system stabilizes with the new firing rate. Understanding this term is crucial for a Machinist's Mate, as maintaining proper water levels is essential for boiler operation and safety.