The Steam Engine Safety Valve: New Valves Require Knowledge of Old Boilers

What you need to know before buying a valve for your hand-fired boiler

The purpose of safety valves for hand-fired boilers have changed from 1909 to today. A safety valve from 1909 (left) was meant to give notice of the highest pressure permissible, according to the American Society of Mechancial Engineers, and to give alarm that more water or less fuel was needed. (See "The Purpose of a Safety Valve" at the end of this article to learn more.
Figures courtesy of Bruce E. Babcock