What do the letters "O" and "S" on an Ashton type safety valve indicate?

The letters "O" and "S" on an Ashton type safety valve signify "Open" and "Shut," respectively. In the context of safety valves, these indicators are crucial for understanding the valve's function during operation. The "O" indicates that the valve is in an open position, which allows for the flow of fluid or gas, while the "S" indicates that it is shut, preventing flow.

This clear labeling aids operators in quickly assessing the status of the valve during critical operating conditions, ensuring safety and proper functioning of the system. Understanding these indicators is essential for maintaining the reliability of safety mechanisms in engineering applications, particularly in pressure control and safety relief systems.