3rd Class Power Engineering (3B1) Practice Exam 2026 - Free 3rd Class Power Engineering Practice Questions and Study Guide

Once through boilers are a category of forced circulation boilers that are designed to have water continuously flow through the heater section and into the steam generator without any accumulation of water. In this type of boiler, water is fed into the system at high pressure, heated to saturation temperature, and then converted to steam in a single pass through the boiler tubes. This design allows for efficient heat transfer and minimizes the potential for overheating and other issues associated with water accumulation.

The distinct operational process of once through boilers makes them particularly suitable for high-capacity, high-efficiency applications, often in power generation. They can also handle changes in load conditions effectively due to their ability to regulate flow rates and operate at varying pressures without impacting performance significantly.

Other categories mentioned, such as constant pressure boilers or multi-fuel boilers, may involve different operational principles or design features that do not specifically align with the forced circulation requirements as seen in once through boilers.