Seemingly out of place with white pipes and atmospheric electric water heaters, what is the use of this ugly valve?
In fact, this valve is so important that its real name is not "bleed valve" in the account, but "relief valve" or "relief valve". As the name suggests, its purpose is to keep the water heater safe:

1. Prevent the explosion caused by uneven pressure
In those days, the boiler always exploded every three or five times, the most important reason is that the boiler entered the air. In the heating process, the gas expansion coefficient is greater, resulting in uneven pressure inside the tank - if the tank wall happens to be uneven or even broken (mostly caused by scale corrosion), an explosion will occur.