Overview:
This 1856 book, “A Catechism of the Steam Engine”, by John Bourne, C.E., serves as a comprehensive guide to understanding the steam engine in its various applications. The book adopts a question and answer format, guiding the reader through the mechanics of the steam engine, its construction, and its uses in mines, mills, navigation, railways, and agriculture.
The author begins by explaining the basic principles of vacuum, pressure, and momentum, setting the foundation for understanding the mechanics of the steam engine. He then delves into the essential components of a steam engine, including the boiler, the engine itself, the air pump, the condenser, and the various pumps associated with these systems.
Key Findings:
- Importance of Expansion: The book emphasizes the importance of working engines expansively, highlighting its significant contribution to fuel efficiency. The author discusses various methods of implementing expansion, including the use of lap on the valves, wire-drawing, and the application of separate expansion valves.
- Impact of Speed: The catechism analyzes the relationship between engine speed and power output, showcasing the advantages and challenges of high-speed engines.
- Fuel Efficiency: The book extensively explores the factors influencing the efficiency of steam engines, particularly the impact of boiler design and the importance of slow combustion for maximizing fuel economy.
- Locomotive Design: The catechism examines the unique design considerations of locomotives, including the use of high-pressure steam, the importance of blast pipe and its effect on draught, and the construction of locomotive boilers.
- Steam Navigation: The book delves into the mechanics of steam navigation, exploring the resistance of vessels in water, the structure and operation of paddle wheels, and the configuration and action of screw propellers.
Learning:
- The Nature of Steam: The reader will learn about the properties of steam, including latent heat, specific heat, and the relationship between pressure, temperature, and volume.
- Steam Engine Components: The book provides detailed explanations of the functions and operation of the various components of a steam engine, including the boiler, cylinder, condenser, pumps, and valves.
- Mechanical Principles: The reader will gain an understanding of crucial mechanical principles, such as friction, momentum, centrifugal and centripetal forces, and the mechanical powers.
- Engine Design and Performance: The catechism offers insights into the design considerations for various types of steam engines, including pumping engines, land engines, marine engines, and locomotives.
- Measuring Efficiency: The reader will learn about the methods used to measure the power and efficiency of steam engines, including the use of the indicator, dynamometer, gauges, and the counter.
Historical Context:
This catechism was written in 1856, a period of significant advancement in steam technology. The Industrial Revolution was in full swing, and the steam engine was playing a pivotal role in driving industrial growth and technological innovation. The book reflects the state-of-the-art in steam engine design and engineering, highlighting the emerging practices and evolving understanding of steam engine efficiency.
Facts:
- Vacuum: A vacuum itself does not exert pressure; it is the pressure of the surrounding atmosphere that is made manifest.
- Air Rush: Air rushes into a vacuum with the velocity a body would acquire falling from the height of a homogeneous atmosphere.
- Falling Bodies: All bodies fall at the same velocity in the absence of air resistance.
- Vis Viva: The “vis viva”, or mechanical energy, of a body increases with the square of its velocity.
- Fly Wheel: The power resident in a fly-wheel rim should be between 2.5 to 4 times greater than the power generated by the engine in one half-stroke.
- Centrifugal Force: Centrifugal force increases as the square of the velocity and is inversely proportional to the radius of the circular path.
- Centre of Gravity: A body hung from its centre of gravity will remain at rest in any position.
- Centre of Gyration: The centre of gyration is the point where the momentum of a revolving body can be considered concentrated.
- Centre of Oscillation: The centre of oscillation of a pendulum is the point where all the mass of the body could be concentrated without affecting its period of vibration.
- Pendulum: The period of vibration of a pendulum is determined by its length, not the arc it describes.
- Conical Pendulum: The conical pendulum or governor operates on the same principles as a simple pendulum.
- Mechanical Powers: All mechanical powers merely transform power, not create it.
- Friction: Friction increases with pressure, but does not increase with velocity.
- Lubrication: The best lubricant for a bearing depends on the pressure and velocity.
- Strength of Materials: Malleable iron has a much higher tensile strength than cast iron, but cast iron has a higher crushing strength.
- Elasticity: The limit of elasticity is the maximum strain a material can withstand without permanent deformation.
- Boiler Pressure: The iron in boilers should not be subjected to a strain exceeding 4,000 lbs. per square inch.
- Boiler Explosions: The most common causes of boiler explosions are high pressure and insufficient strength.
- Scale: Scale is formed in boilers due to the deposition of insoluble salts from water.
- Corrosion: The primary cause of rapid internal corrosion in marine boilers is suspected to be surcharged steam.
Statistics:
- Air for Combustion: A pound of coal requires approximately 240 cubic feet of air for complete combustion.
- Evaporative Power: A pound of the best Welsh coal can evaporate between 9.5 to 10 lbs. of water into steam.
- Steam Expansion: Expanding steam 4 times more than doubles the power output of a given amount of steam.
- Nominal Horse Power: The nominal power of a condensing engine is calculated by squaring the diameter of the cylinder, multiplying by the piston speed, and dividing by 6,000.
- Actual Horsepower: Actual horsepower is calculated by squaring the diameter of the cylinder, multiplying by the pressure (less 1.5 lbs for friction), and the piston speed, and dividing by 42,017.
- Duty of Engines: The duty of a pumping engine is expressed as millions of pounds raised one foot high by a bushel of coal.
- Heating Surface: A cubic foot of water evaporation per hour requires approximately 9 square feet of heating surface in a wagon boiler.
- Fire Grate Surface: Boulton and Watt allow 0.64 square feet of fire grate per nominal horsepower in their marine boilers.
- Calorimeter: The calorimeter of a boiler, or the sectional area of the flue in square inches, is usually between 20 and 25 in marine flue boilers.
- Steam Room: In land wagon boilers, Boulton and Watt allow 8.75 cubic feet of steam room per horsepower.
- Locomotive Performance: A locomotive can evaporate between 16 and 20 cubic feet of water per hour for each square foot of fire grate.
- Blast Pipe Exhaustion: The blast in locomotive boilers can produce an exhaustion equivalent to 6 inches of water.
- Tractive Force: The average tractive force required to draw carriages on railways is about 7.5 lbs. per ton.
- Locomotive Adhesion: The adhesion of locomotive wheels on clean rails is about 1/5th of the weight.
Terms:
- Vacuum: An empty space devoid of matter.
- Vis Viva: The energy of a moving body, measured by the square of its velocity.
- Centrifugal Force: The force that tends to push a body outwards from a circular path.
- Centripetal Force: The force that pulls a body inwards towards a circular path.
- Centre of Gravity: The point within a body where its weight can be considered concentrated.
- Centre of Gyration: The point in a rotating body where its momentum is concentrated.
- Centre of Oscillation: The point in a swinging body where its mass could be concentrated without affecting its period of vibration.
- Expansion: The process of allowing steam to expand in the cylinder after the steam valve is closed.
- Lap: The extra length of the slide valve face over the steam port, which controls the point of steam cutoff and the amount of expansion.
- Lead: The amount of valve opening before the piston starts its stroke.
Examples:
- Wagon Boiler: A long rectangular vessel with a rounded top, similar to a wagon.
- Cornish Boiler: A cylindrical boiler with a large internal flue containing the furnace.
- Marine Flue Boiler: Boilers with furnaces set within the boiler and flues winding back and forth inside.
- Marine Tubular Boiler: Boilers with a large number of small tubes through which smoke passes before entering the chimney.
- Side Lever Engine: A marine engine with two beams or levers on either side of the engine, connected to the piston rod and crank.
- Oscillating Engine: A marine engine with cylinders mounted on trunnions, allowing them to oscillate as the crankshaft rotates.
- Geared Screw Engine: Screw engines that use toothed wheels to increase the speed of the screw shaft.
- Direct Acting Screw Engine: Engines that are directly connected to the screw shaft, requiring higher engine speeds.
- Locomotive Engine: A high-pressure steam engine mounted on wheels, designed for use on railways.
- Cornish Pumping Engine: A single-acting beam engine used for pumping water, often employing high-pressure steam and expansion techniques.
Conclusion:
This catechism serves as a valuable resource for understanding the steam engine, its mechanics, and its diverse applications. The book provides a comprehensive and detailed guide to the steam engine, covering the key principles, components, and design considerations of this fundamental technology. It highlights the importance of fuel efficiency, expansion techniques, and the challenges and advantages of high-speed engines. The catechism also offers insights into the historical context of steam technology, reflecting the rapid advancement and widespread adoption of the steam engine during the Industrial Revolution.