Locomotive/marine boiler safety valve: commonly used type Select the safety valve type predominantly used on locomotive and marine boilers, where orientation and vibration demand a non-gravity mechanism. Choose the correct option.

Concept
Locomotive and marine boilers experience motion, vibration, and attitude changes, making gravity-based valves unsuitable. Spring-loaded safety valves maintain set pressure independent of orientation and are compact and responsive.

Why others are wrong
Lever and dead-weight types rely on gravity and are more suited to stationary land boilers. A high-steam/low-water valve is a different protective device, not the standard main safety valve.

Final Answer
Spring loaded safety valve