Safety valve is a device used in various mechanical systems to relieve pressure. Such systems include nuclear reactors, steam boilers, maintenance-free car batteries, and water heaters. A safety valve assures that the system does not exceed the pressure for which it is designed. If the pressure in the system rises to a maximum predetermined value, called the valve set pressure, the safety valve opens and releases steam or some other gas, causing the pressure to fall.
A common type of safety valve consists of a cone-shaped vent into which an insert called a valve seat is fitted. In some safety valves, the valve seat is held in place by a lever bearing a weight. The valve set pressure can be raised or lowered by moving the weight on the lever. But most safety valves use a compressed spring instead of a weight. Spring safety valves are called pop safety valves. The valve set pressure can be adjusted by varying the degree of compression in the spring.
See also Bismuth .
