Boiler types — applicability of the high-steam & low-water safety valve The combined high-steam and low-water safety valve is <i>not</i> used on which of the following boilers?

Introduction / Context:
The high-steam and low-water safety valve is a combined device that both relieves overpressure and provides protection if water level becomes dangerously low. Its use depends on boiler construction and service. This question targets where it is generally not employed.

Given Data / Assumptions:

• Cornish and Lancashire are stationary, internally fired, fire-tube boilers with ample shell water space.
• Cochran is a vertical, fire-tube boiler commonly fitted with simple safety valves.
• Locomotive boilers have distinct arrangements and operating dynamics (high vibration, varying water levels, separate low-water protection like fusible plugs).

Concept / Approach:
Locomotive boilers typically use spring-loaded safety valves for overpressure and fusible plugs for low-water protection, rather than the combined high-steam & low-water safety valve used on certain stationary shell boilers. Hence, the combined type is generally not applied to locomotive boilers.

Step-by-Step Solution:

Verification / Alternative check:
Standard boiler texts list the combined valve with Cornish and Lancashire; locomotive sections emphasize Ramsbottom or Pop safety valves plus fusible plugs.

Why Other Options Are Wrong:

• Cochran, Cornish, Lancashire: classic stationary types that may use the combined valve.
• Generic vertical fire-tube: context-dependent; many use simple safety valves but the question’s conventional exclusion remains the locomotive boiler.

Common Pitfalls:
Assuming one style of safety device suits all boilers; ignoring the specialized locomotive operating environment.

Final Answer: