Typical length of a Lancashire boiler shell Select the usual industrial range for the overall shell length of a Lancashire boiler (excluding external fittings):

Introduction / Context:
The Lancashire boiler evolved from the Cornish design to provide higher capacity via two furnace flues. Basic dimensional ranges are common exam points because they reflect practical fabrication, stress, and installation constraints for shell boilers.

Given Data / Assumptions:

• Conventional steel shell construction with two internal furnace tubes.
• Low-to-medium pressure service.
• Length measured over the cylindrical shell body.

Concept / Approach:
Standard Lancashire boilers are relatively long to accommodate adequate heating surface and gas travel while maintaining manageable shell stresses and draft. Textbook and manufacturer data commonly cite overall shell lengths in the roughly 7.25–9 m range for typical units, with diameters around 2–3 m, though larger custom units exist.

Step-by-Step Solution:
Recall typical dimensional data from standard references.Match the commonly quoted range 7.25–9 m.Select option reflecting that range.

Verification / Alternative check:
Historic catalogues and exam manuals list Lancashire shell lengths around 24–30 ft (≈7.3–9.1 m), aligning with the selected option.

Why Other Options Are Wrong:
5–7 m is on the short side for classic two-flue designs; 9–10 m can exist but is beyond the usual cited “typical” range; “greater than 12 m” is atypical for standard patterns and would require special design considerations.

Common Pitfalls:
Confusing furnace tube length with overall shell length; assuming all shells follow one fixed dimension rather than a range.

Final Answer:
7.25 to 9 m