It consists of a cone-shaped vent into which a plug is fitted. This plug is held in place by a lever bearing a weight. The maximum steam pressure in the boiler can be increased or decreased by shifting the weight on the lever.
Many safety valves use a spring instead of a weight.
This is because a spring is less subject to accident. Spring safety valves are called pop safety valves. Hot water heaters also have safety valves. See also Bismuth . Valtek Inc. How to cite this article.