--- title: "Lancashire boiler construction and working" subject: "Applied Thermodynamics" chapter: 1 key: "semester_3/applied_thermodynamics:lancashire-boiler-working" source: https://www.bctengineer.com/q/semester_3/applied_thermodynamics/lancashire-boiler-working site: BCT Engineering --- # Lancashire boiler construction and working Applied Thermodynamics · Chapter 1: Boilers - Asked in: year not given, 8 marks - Video: [Lancashire boiler in hindi || working of lancashire boiler || Explain lancashire boiler](https://www.youtube.com/watch?v=Hyo6c7JJ9wQ) — Gear Institute Mechanical Engineering Videos and Physics by Gear Institute - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_3/applied_thermodynamics/lancashire-boiler-working - Whole chapter: https://www.bctengineer.com/md/semester_3/applied_thermodynamics/chapter-1 ## Question Describe the construction and working of a Lancashire boiler with a neat sketch. List its mountings. ## Short answer It is a horizontal, internally-fired fire-tube boiler with two large furnace tubes inside a water-filled shell. Hot gases travel through the tubes (first pass), then bottom flue (second pass), and side flues (third pass) to chimney. Essential mountings include safety valves, water gauge, fusible plug, stop valve, and feed check valve. ## Answer A **Lancashire boiler** is a horizontal, internally fired, natural-circulation fire tube boiler with two large furnace tubes (flues) running through the shell. It is a stationary boiler for medium pressure. #### Construction - A cylindrical shell about 2 to 3 m in diameter and 7 to 9 m long, set in brickwork and filled with water to well above the furnace tubes. - Two large-diameter furnace tubes pass lengthwise through the shell. The grate is at the front end of each tube. - The brickwork forms a bottom flue under the shell and two side flues along its sides. - Typical rating: pressure up to about 16 bar and steam output up to about 8 t/h. ```text Steam stop valve Safety valves \ / ______[=====steam space=====]____ | front <---- water ---- rear | | ===== furnace tube 1 =====> | | ===== furnace tube 2 =====> | |___________ shell ____________| grate | bottom flue | ----> hot gas path: | tubes (1st pass) -> bottom flue (2nd pass, to front) -> side flues (3rd pass) -> chimney ``` #### Working 1. Fuel burns on the grates inside the furnace tubes. 2. Hot gases travel to the rear through the furnace tubes (first pass), heating the water. 3. At the rear they turn downward into the bottom flue and flow forward under the shell (second pass). 4. At the front they divide into the two side flues and flow backward (third pass), then reach the chimney through sliding dampers that control the draught. 5. Steam collects in the steam space and is taken out through the stop valve (an anti-priming pipe or steam separator can be fitted). #### Mountings Water level gauge, pressure gauge, safety valve (dead-weight or spring-loaded), high-steam low-water safety valve, fusible plug (on the furnace tubes), steam stop valve, feed check valve, blow-off cock, manhole and mud hole. **Merits:** simple, reliable, large water reserve, easy to operate and clean. **Demerits:** slow steaming, large floor space, low pressure and capacity. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. A Lancashire boiler is best described as A. a vertical, externally fired water tube boiler with forced circulation B. an inclined water tube boiler with a single furnace tube C. a vertical fire tube boiler with a cross tube D. a horizontal, internally fired, natural-circulation fire tube boiler with two furnace tubes Answer: D. It is a horizontal, internally fired fire tube boiler with two large furnace tubes through the shell. (Key point: Type of boiler) 2. What is the correct path of the hot gases in a Lancashire boiler? A. Furnace tubes to rear, then bottom flue forward, then side flues backward, then chimney B. Side flues first, then furnace tubes, then bottom flue, then chimney C. Bottom flue to rear, then furnace tubes forward, then chimney D. Straight through the furnace tubes to the chimney in a single pass Answer: A. Gases pass back through the furnace tubes (1st pass), forward under the shell (2nd pass), and backward in the side flues (3rd pass). (Key point: Gas path) 3. Which list contains mountings of a Lancashire boiler? A. Economiser, air preheater, superheater, feed pump B. Water level gauge, safety valve, fusible plug, feed check valve C. Mud box, uptake header, downtake header D. Injector, steam trap, water softener Answer: B. Mountings include water level gauge, pressure gauge, safety valve, fusible plug, stop valve, feed check valve, blow-off cock and manhole. (Key point: Mountings) 4. Which is a demerit of the Lancashire boiler? A. Quick steam raising from small water content B. Cannot be cleaned easily C. Slow steaming and large floor space D. Very high pressure capability Answer: C. Because of its large water reserve it steams slowly, needs much floor space and gives only low pressure and capacity. 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