117 Boulton and Watt

25.3.2: Boulton and Watt

The Boulton and Watt steam engine led to replacing the water wheel and horses as the main sources of power for British industry, thereby freeing it from geographical constraints and becoming one of the main drivers in the Industrial Revolution.

Learning Objective

Recognize why Boulton and Watt’s steam engine achieved widespread success

Key Points

  • In 1763, James Watt, an instrument maker at the University of Glasgow, was assigned the job of repairing a model Newcomen engine (based on an earlier design of the Savery engine) and noted how inefficient it was. In 1765, Watt conceived the idea of equipping the engine with a separate condensation chamber, which he called a condenser. Because the condenser and the working cylinder were separate, condensation occurred without significant loss of heat from the cylinder. This invention dramatically improved the efficiency of the engine.
  • Watt’s next improvement to the Newcomen design was to seal the top of the cylinder and surround the cylinder with a jacket. Steam was passed through the jacket before being admitted below the piston, keeping the piston and cylinder warm to prevent condensation within it. These improvements led to the fully developed version of 1776 that actually went into production.
  • The separate condenser showed dramatic potential for improvements on the Newcomen engine, but Watt was still discouraged by seemingly insurmountable problems before a marketable engine could be perfected. It was only after entering into partnership with Matthew Boulton that this became reality. Boulton and Watt became an engineering company that was critical to the technological advancements of the Industrial Revolution.
  • As fully developed, the Watt engine used about 75% less fuel than a similar Newcomen one. Boulton and Watt’s practice was to help mine owners and other customers build engines, supplying men to erect them and specialized parts. However, their main profit from their patent was derived from charging a licence fee to the engine owners based on the cost of the fuel they saved. The greater fuel efficiency of their engines meant that they were most attractive in areas where fuel was expensive.
  • Later improvements introduced by Watt included an arrangement of valves that could alternately admit low pressure steam to the cylinder and connect with the condenser (the double acting piston); parallel motion; transforming the action of the beam into a rotating motion (first by the epicyclic sun and planet gear system suggested by an employee William Murdoch and later by connecting the beam to a wheel by a crank after patent rights on the use of the crank expired), and linking a steam regulator valve to a centrifugal governor to keep a constant speed.
  • These improvements allowed the steam engine to replace the water wheel and horses as the main sources of power for British industry, thereby freeing it from geographical constraints and allowing it to become one of the main drivers in the Industrial Revolution.

Key Terms

atmospheric engine
An engine invented by Thomas Newcomen in 1712, often referred to simply as a Newcomen engine. The engine operated by condensing steam drawn into the cylinder, thereby creating a partial vacuum and allowing the atmospheric pressure to push the piston into the cylinder. It was the first practical device to harness steam to produce mechanical work.
condenser
A device or unit used to condense a substance from its gaseous to its liquid state by cooling it, which transfers the latent heat from the substance to the condenser coolant. These devices are typically heat exchangers, which have various designs and come in many sizes ranging from rather small (hand-held) to very large industrial-scale units used in plant processes.
Boulton and Watt
An early British engineering and manufacturing firm in the business of designing and making marine and stationary steam engines. Founded in the English West Midlands around Birmingham in 1775 as a partnership between the English manufacturer Matthew Boulton and the Scottish engineer James Watt, the firm had a major role in the Industrial Revolution and grew to be a major producer of steam engines in the 19th century.
parallel motion
A mechanical linkage invented by the Scottish engineer James Watt in 1784 for the double-acting Watt steam engine. It allows a rod moving straight up and down to transmit motion to a beam moving in an arc, without putting sideways strain on the rod.
reciprocating engine
A heat engine also known as a piston engine that uses one or more reciprocating pistons to convert pressure into a rotating motion. The main types are the internal combustion engine, used extensively in motor vehicles; the steam engine, the mainstay of the Industrial Revolution; and the niche application Stirling engine.

 

James Watt: Improving the Newcomen Engine

In 1698, English mechanical designer Thomas Savery invented a pumping appliance that used steam to draw water directly from a well by means of a vacuum created by condensing steam. The appliance was also proposed for draining mines, but could only draw fluid up approximately 25 feet, meaning it had to be located within this distance of the mine floor. As mines became deeper, this was often impractical. The solution to draining deep mines was found by Thomas Newcomen, who developed an atmospheric engine that also worked on the vacuum principle. The Newcomen engine was more powerful than the Savery engine. For the first time, water could be raised from a depth of over 150 feet. However, while Newcomen engines brought practical benefits, they were inefficient in terms of energy use. The system of alternately sending jets of steam then cold water into the cylinder meant that the walls of the cylinder were alternately heated then cooled with each stroke. Each charge of steam introduced would continue condensing until the cylinder approached working temperature again, so at each stroke part of the potential of the steam was lost.

In 1763, James Watt was working as instrument maker at the University of Glasgow when he was assigned the job of repairing a model Newcomen engine and noted how inefficient it was. In 1765, Watt conceived the idea of equipping the engine with a separate condensation chamber, which he called a condenser. Because the condenser and the working cylinder were separate, condensation occurred without significant loss of heat from the cylinder. The condenser remained cold and below atmospheric pressure at all times, while the cylinder remained hot at all times. Steam was drawn from the boiler to the cylinder under the piston. When the piston reached the top of the cylinder, the steam inlet valve closed and the valve controlling the passage to the condenser opened. The lower pressure of the condenser, drew the steam into the cylinder where it cooled and condensed from water vapor to liquid water, maintaining a partial vacuum in the condenser that was communicated to the space of the cylinder by the connecting passage. External atmospheric pressure then pushed the piston down the cylinder.

The separation of the cylinder and condenser eliminated the loss of heat that occurred when steam was condensed in the working cylinder of a Newcomen engine. This gave the Watt engine greater efficiency than the Newcomen engine, reducing the amount of coal consumed while doing the same amount of work. In Watt’s design, the cold water was injected only into the condensation chamber. This type of condenser is known as a jet condenser.

Watt’s next improvement to the Newcomen design was to seal the top of the cylinder and surround it with a jacket. Steam was passed through the jacket before being admitted below the piston, keeping the piston and cylinder warm to prevent condensation within it. Watt did not use high-pressure steam because of safety concerns, although he was aware of its potential and included expansive working knowledge in his patent of 1782. These improvements led to the fully developed version of 1776 that actually went into production.

 

Boulton and Watt Join Forces

The separate condenser showed dramatic potential for improvements on the Newcomen engine but Watt was still discouraged by seemingly insurmountable problems before a marketable engine could be perfected. It was only after entering into partnership with Matthew Boulton that this became reality. Watt told Boulton about his ideas on improving the engine and Boulton, an avid entrepreneur, agreed to fund development of a test engine at Soho, near Birmingham. At last Watt had access to facilities and the practical experience of craftsmen who were soon able to get the first engine working. As fully developed, it used about 75% less fuel than a similar Newcomen model.

The major components of a Watt pumping engine, Robert H. Thurston, History of the Growth of the Steam Engine, D. Appleton & Co, 1878.

The Boulton and Watt steam engine (known also as the Watt engine), developed sporadically from 1763 to 1775, was an improvement on the design of the Newcomen engine and was a key point in the Industrial Revolution.

The schematic shows the parts of the watt steam pumping engine, including: pump, hot feed water delivery to boiler, plug rod, transfer pipe, hot well, cold water tank, vacuum pump, condenser, vacuum end of cylinder, steam jacket, piston, and low pressure steam end of cylinder.

In 1775, Watt designed two large engines: one for the Bloomfield Colliery at Tipton and one for John Wilkinson’s ironworks at Willey, Shropshire, both completed in 1776. A third engine, at Stratford-le-Bow in east London, was also working that year. Boulton and Watt’s practice was to help mine owners and other customers build engines, supplying men to erect them and specialized parts. However, the main profit from their patent was derived from charging a license fee to the engine owners, based on the cost of the fuel they saved. The greater fuel efficiency of their engines meant that they were most attractive in areas where fuel was expensive, particularly Cornwall, for which three engines were ordered in 1777.

 

Later Improvements

The first Watt engines were atmospheric pressure engines, like the Newcomen engine but with the condensation separated from the cylinder. Driving the engines using both low pressure steam and a partial vacuum raised the possibility of reciprocating engine development. An arrangement of valves could alternately admit low-pressure steam to the cylinder and connect with the condenser. Consequently, the direction of the power stroke might be reversed, making it easier to obtain rotary motion. Additional benefits of the double-acting engine were increased efficiency, higher speed (greater power), and more regular motion.

Before the development of the double-acting piston, e to the beam and the piston rod were linked by a chain, which meant that power could only be applied in one direction, by pulling. This was effective in engines used for pumping water, but the double action of the piston meant that it could push as well as pull. Further, it was not possible to connect the piston rod of the sealed cylinder directly to the beam, because while the rod moved vertically in a straight line, the beam was pivoted at its center with each side inscribing an arc. To bridge the conflicting actions of the beam and the piston, Watt developed his parallel motion. This masterpiece of engineering uses a four-bar linkage coupled with a pantograph (a type of current collector)to produce the required straight-line motion much more cheaply than if he had used a slider type of linkage. He was very proud of his solution.

Watt’s parallel motion on a pumping engine

In a letter to his son in 1808, James Watt wrote, “I am more proud of the parallel motion than of any other invention I have ever made.” The sketch he included actually shows what is now known as Watt’s linkage, which was described in Watt’s 1784 patent but was immediately superseded by the parallel motion. The parallel motion differed from Watt’s linkage by having an additional pantograph linkage incorporated in the design. This did not affect the fundamental principle but it allowed the engine room to be smaller because the linkage was more compact.

Having the beam connected to the piston shaft by a means that applied force alternately in both directions also meant that the motion of the beam could be used to turn a wheel. The simplest solution to transforming the action of the beam into a rotating motion was to connect the beam to a wheel by a crank, but because another party had patent rights on the use of the crank, Watt was obliged to come up with another solution. He adopted the epicyclic sun and planet gear system suggested by employee William Murdoch, only later reverting, once the patent rights had expired, to the more familiar crank seen on most engines today. The main wheel attached to the crank was large and heavy, serving as a flywheel that once set in motion, by its momentum maintained a constant power and smoothed the action of the alternating strokes. To its rotating central shaft, belts and gears could be attached to drive a great variety of machinery. Because factory machinery needed to operate at a constant speed, Watt linked a steam regulator valve to a centrifugal governor, which he adapted from those used to automatically control the speed of windmills.

These improvements allowed the steam engine to replace the water wheel and horses as the main sources of power for British industry, thereby freeing it from geographical constraints and becoming one of the main drivers in the Industrial Revolution. Watt was also concerned with fundamental research on the functioning of the steam engine. His most notable measuring device, still in use today, is the Watt indicator, incorporating a manometer to measure steam pressure within the cylinder according to the position of the piston. This enabled a diagram to be produced representing the pressure of the steam as a function of its volume throughout the cycle.

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