Steam drum is the reservoir at the top of the water tube boiler. The water tubes which carry water are connected to the Steam drum. The steam drum serves to extract the steam from the water and send it for superheating. The difference in density causes the steam to rise.
The pressure in the steam drum regulates the steam generation within the boiler. As the steam is extracted, further steam is generated.
The water is sent back to the water drum for further heating.
