Why are some of the tube ends in a water tube boiler beaded?

In a water tube boiler, the beading of some tube ends serves a critical function in preventing air pockets in the lower drums. The beading creates a tighter seal and guides the flow of water through the tubes, ensuring that water is efficiently circulated and heated throughout the system. This is particularly important because air pockets can lead to reduced heat transfer and can create hot spots in the boiler, which can compromise the integrity and efficiency of the boiler over time. By ensuring a continuous flow of water and minimizing air entrapment, the beaded ends contribute to the overall operational effectiveness of the water tube boiler, enhancing its reliability and performance.