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An 1817 Boulton & Watt beam blowing engine, used in Netherton at the ironworks of M W Grazebrook. Re-erected on the A38(M) in Birmingham, UK

Preserved British steam-powered fire engine – an example of a mobile steam engine. This is a horse-drawn vehicle: the steam engine drives the water pump

A mill engine from Stott Park Bobbin Mill, Cumbria, England

A steam engine is a heat engine that performs mechanical work using steam as its working fluid.

Steam engines are external combustion engines,^[1] where the working fluid is separate from the combustion products. Non-combustion heat sources such as solar power, nuclear power or geothermal energy may be used. Water turns to steam in a boiler and reaches a high pressure. When expanded through pistons or turbines, mechanical work is done. The reduced-pressure steam is then released into the atmosphere or condensed and pumped back into the boiler. The ideal thermodynamic cycle used to analyze this process is called the Rankine cycle. Most mobile steam engines and some smaller stationary engines discard the low-pressure steam instead of condensing it for reuse.

The idea of using boiling water to produce mechanical motion has a very long history, going back about 2,000 years. Early devices were not practical power producers, but more advanced designs producing usable power have become a major source of mechanical power over the last 300 years, beginning with applications for removing water from mines using vacuum engines. Subsequent developments used pressurized steam and converted linear to rotational motion which enabled the powering of a wide range of manufacturing machinery. These engines could be sited anywhere that water and coal or wood fuel could be obtained, whereas previous installations were limited to locations where water wheels or windmills could be used. Significantly, this power source would later be applied to vehicles such as steam tractors and railway locomotives. The steam engine was a critical component of the Industrial Revolution, providing the prime mover for modern mass-production manufacturing methods. Modern steam turbines generate about 90% of the electric power in the United States using a variety of heat sources.^[2]

In general usage, the term 'steam engine' can refer to integrated steam plants such as railway steam locomotives and portable engines, or may refer to the machinery alone, as in the beam engine and stationary steam engine. Specialized devices such as steam hammers and steam pile drivers are dependent on steam supplied from a separate boiler.

History[link]

An aeolipile rotates due to the steam escaping from the arms. No practical use was made of this effect.

The history of the steam engine stretches back as far as the first century AD; the first recorded rudimentary steam engine being the aeolipile described by Greek mathematician Hero of Alexandria.^[3] In the following centuries, the few steam-powered 'engines' known about were essentially experimental devices used by inventors to demonstrate the properties of steam. A rudimentary steam turbine device was described by Taqi al-Din^[4] in 1551 and by Giovanni Branca^[5] in 1629.^[6] Denis Papin a Huguenot refugee did some useful work on the steam digester in 1679, and first used a piston to raise weights in 1690.

The first practical steam-powered 'engine' was a water pump, developed in 1698 by Thomas Savery. It used a vacuum to raise water from below, then used steam pressure to raise it higher. Small engines were effective though larger models were problematic.They proved only to have a limited lift height and were prone to boiler explosions. It received some use in mines and pumping stations. ^[7]

The first commercially successful engine was the atmospheric engine, invented by Thomas Newcomen around 1712.^[8] It made use of technologies discovered by Savery and Papin. Newcomen's engine was relatively inefficient, and in most cases was used for pumping water. It worked by creating a partial vacuum by condensing steam in a cylinder. It was employed for draining mine workings at depths hitherto impossible, and also for providing a reusable water supply for driving waterwheels at factories sited away from a suitable 'head'. Water that had passed over the wheel was pumped back up into a storage reservoir above the wheel.

In 1720 Jacob Leupold built a two cylinder high pressure steam engine.^[9] The invention was published in his major work "Theatri Machinarum Hydraulicarum".^[10] The engine used two lead-weighted pistons providing a continuous motion to a water pump. Each piston was raised by the steam pressure and returned to its original position by gravity. The two pistons shared a common four way rotary valve connected directly to a steam boiler.

Jacob Leupold Steam engine 1720

Early Watt pumping engine

John Smeaton made significant mechanical improvements to the Newcomen engine, most importantly better piston sealing, around the time James Watt was building his first engines (ca. late 1770s).^[11]

The next major step occurred when James Watt developed (1763–75) an improved version of Newcomen's engine, with a separate condenser. Boulton and Watt's early engines used half as much coal as the Smeaton improved version of Newcomen's.^[11] Newcomen's and Watt's early engines were "atmospheric". They were powered by air pressure pushing a piston into the partial vacuum generated by condensing steam, instead of the pressure of expanding steam. The engine Cylinders had to be large because the only usable force acting on them was due to atmospheric pressure.

Watt proceeded to develop his engine further, modifying it to provide a rotary motion suitable for driving factory machinery. This enabled factories to be sited away from rivers, and further accelerated the pace of the Industrial Revolution.

Around 1800, Richard Trevithick and separately Oliver Evans (1801)^[12][13] introduced engines using high-pressure steam, although Trevithick had obtained a high pressure engine patent in 1782.^[14] These were much more powerful for a given cylinder size than previous engines and could be made small enough for transport applications. Thereafter, technological developments and improvements in manufacturing techniques (partly brought about by the adoption of the steam engine as a power source) resulted in the design of more efficient engines that could be smaller, faster, or more powerful, depending on the intended application.

The Corliss steam engine, a four-valve counterflow engine with separate steam admission and exhaust valves and automatic variable steam cut off, was called the most significant advance in the steam engine since James Watt. In addition to using 30% less steam it provided more uniform speed, making it well suited to manufacturing, especially cotton spinning.^[14][12]

Near the end of the 19th century compound engines came into widespread use. Compound engines exhausted steam in to successively larger cylinders to accommodate the higher volumes at reduced pressures, giving improved efficiency. These stages were called expansions, with double and triple expansion engines being used, especially in shipping where efficiency was important to reduce the weight of coal carried.^[14]

The final major evolution of the steam engine design was the switch from pistons to turbines starting in the early part of the 20th century. Turbines are more efficient than pistons, have fewer moving parts, and provide rotative power directly instead of through a connecting rod system or similar means.

Steam engines remained the dominant source of power well into the 20th century, when advances in the design of electric motors and internal combustion engines gradually resulted in the replacement of reciprocating (piston) steam engines in commercial usage, and the ascendancy of steam turbines in power generation. Today most steam power is provided by turbines.

Steam cycle[link]

Physical layout of the four main devices used in the Rankine cycle. Other components that perform the same or similar functions are often used, the turbine is often replaced with a steam driven piston.

The Rankine cycle is the fundamental thermodynamic underpinning of the steam engine. The Rankine cycle is a cycle that converts heat into work. The heat is supplied externally to a closed loop, which in steam engines contains water and steam. This cycle generates about 90% of all electric power used throughout the world, including virtually all solar thermal, biomass, coal and nuclear power plants. It is named after William John Macquorn Rankine, a Scottish polymath.

The Rankine cycle is sometimes referred to as a practical Carnot cycle because, when an efficient turbine is used, the TS diagram begins to resemble the Carnot cycle. The main difference is that heat addition (in the boiler) and rejection (in the condenser) are isobaric (constant pressure) in the Rankine cycle and isothermal (constant temperature) in the theoretical Carnot cycle. In this cycle a pump is also used to pressurize the working fluid received from the condenser as a liquid instead of as a gas. Pumping the working fluid through the cycle as a liquid requires a very small fraction of the energy needed to transport it as compared to compressing the working fluid as a gas in a compressor (as in the Carnot cycle).

The working fluid in a Rankine cycle follows a closed loop and is reused constantly. While many substances could be used in the Rankine cycle, water is usually the fluid of choice due to its favourable properties, such as non-toxic and unreactive chemistry, abundance, and low cost, as well as its thermodynamic properties.

Components of steam engines[link]

There are two fundamental components of a steam plant: the boiler or steam generator, and the "motor unit", referred to itself as a "steam engine". Stationary steam engines in fixed buildings may have the two parts in separate buildings some distance apart. For portable or mobile use, such as steam locomotives, the two are mounted together.

The engine itself typically consisted of a cast iron cylinder, piston, connecting rod and beam or a crank and flywheel, and miscellaneous linkages. Steam was alternately supplied and exhausted by one or more valves. Speed control was either automatic, using a governor, or by a manual valve. The cylinder casting contained steam supply and exhaust ports.

Engines equipped with a condenser are a separate type than those that exhaust to the atmosphere.

Other components are often present; pumps (such as an injector) to supply water to the boiler during operation, condensers to recirculate the water and recover the latent heat of vaporisation, and superheaters to raise the temperature of the steam above its saturated vapour point, and various mechanisms to increase the draft for fireboxes. When coal is used, a chain or screw stoking mechanism and its drive engine or motor may be included to move the fuel from a supply bin (bunker) to the firebox.

Heat source[link]

The heat required for boiling the water and supplying the steam can be derived from various sources, most commonly from burning combustible materials with an appropriate supply of air in a closed space (called variously combustion chamber, firebox). In some cases the heat source is a nuclear reactor or geothermal energy.

Boilers[link]

An industrial boiler used for a stationary steam engine

Boilers are pressure vessels that contain water to be boiled, and some kind of mechanism for transferring the heat to the water so as to boil it.

The two most common methods of transferring heat to the water are:

1. water-tube boiler - water is contained in or run through one or several tubes surrounded by hot gases
2. fire-tube boiler - the water partially fills a vessel below or inside which is a combustion chamber or furnace and fire tubes through which the hot gases flow

Fire tube boilers were the main type used for early high pressure steam, but they were displaced by safer water tube boilers in the late 19th century.^[14]

Once turned to steam, many boilers raise the temperature of the steam further, turning 'wet steam' into 'superheated steam'. This use of superheating avoids the steam condensing within the engine, and allows significantly greater efficiency.

Motor units[link]

A motor unit takes a supply of steam at high pressure and temperature and gives out a supply of steam at lower pressure and temperature, using as much of the difference in steam energy as possible to do mechanical work.

A motor unit is often called 'steam engine' in its own right. They will also operate on compressed air or other gas.

Simple expansion[link]

This means that a charge of steam works only once in the cylinder. It is then exhausted directly into the atmosphere or into a condenser, but remaining heat can be utilized if needed to heat a living space, or to provide warm feedwater for the boiler.

Double acting stationary engine. This was the common mill engine of the mid 19th century. Note the slide valve with concave, almost "D" shaped, seat side.

Schematic Indicator diagram showing the four events in a double piston stroke. See: Monitoring equipment (below)

In most reciprocating piston engines, the steam reverses its direction of flow at each stroke (counterflow), entering and exhausting from the cylinder by the same port. The complete engine cycle occupies one rotation of the crank and two piston strokes; the cycle also comprises four events – admission, expansion, exhaust, compression. These events are controlled by valves often working inside a steam chest adjacent to the cylinder; the valves distribute the steam by opening and closing steam ports communicating with the cylinder end(s) and are driven by valve gear, of which there are many types. The simplest valve gears give events of fixed length during the engine cycle and often make the engine rotate in only one direction. Most however have a reversing mechanism which additionally can provide means for saving steam as speed and momentum are gained by gradually "shortening the cutoff" or rather, shortening the admission event; this in turn proportionately lengthens the expansion period. However, as one and the same valve usually controls both steam flows, a short cutoff at admission adversely affects the exhaust and compression periods which should ideally always be kept fairly constant; if the exhaust event is too brief, the totality of the exhaust steam cannot evacuate the cylinder, choking it and giving excessive compression ("kick back").

In the 1840s and 50s, there were attempts to overcome this problem by means of various patent valve gears with a separate, variable cutoff expansion valve riding on the back of the main slide valve; the latter usually had fixed or limited cutoff. The combined setup gave a fair approximation of the ideal events, at the expense of increased friction and wear, and the mechanism tended to be complicated. The usual compromise solution has been to provide lap by lengthening rubbing surfaces of the valve in such a way as to overlap the port on the admission side, with the effect that the exhaust side remains open for a longer period after cut-off on the admission side has occurred. This expedient has since been generally considered satisfactory for most purposes and makes possible the use of the simpler Stephenson, Joy and Walschaerts motions. Corliss, and later, poppet valve gears had separate admission and exhaust valves driven by trip mechanisms or cams profiled so as to give ideal events; most of these gears never succeeded outside of the stationary marketplace due to various other issues including leakage and more delicate mechanisms.^[15][16]

Compression

Before the exhaust phase is quite complete, the exhaust side of the valve closes, shutting a portion of the exhaust steam inside the cylinder. This determines the compression phase where a cushion of steam is formed against which the piston does work whilst its velocity is rapidly decreasing; it moreover obviates the pressure and temperature shock, which would otherwise be caused by the sudden admission of the high pressure steam at the beginning of the following cycle.

Lead

The above effects are further enhanced by providing lead: as was later discovered with the internal combustion engine, it has been found advantageous since the late 1830s to advance the admission phase, giving the valve lead so that admission occurs a little before the end of the exhaust stroke in order to fill the clearance volume comprising the ports and the cylinder ends (not part of the piston-swept volume) before the steam begins to exert effort on the piston.^[17]

Oscillating cylinder steam engines[link]

Operation of a simple oscillating cylinder steam engine

An oscillating cylinder steam engine is a variant of the simple expansion steam engine which does not require valves to direct steam into and out of the cylinder. Instead of valves, the entire cylinder rocks, or oscillates, such that one or more holes in the cylinder line up with holes in a fixed port face or in the pivot mounting (trunnion). These engines are mainly used in toys and models, because of their simplicity, but have also been used in full size working engines, mainly on ships where their compactness is valued.

Compound engines[link]

As steam expands in a high pressure engine its temperature drops because no heat is added to the system; this is known as adiabatic expansion and results in steam entering the cylinder at high temperature and leaving at low temperature. This causes a cycle of heating and cooling of the cylinder with every stroke which is a source of inefficiency.

A method to lessen the magnitude of this heating and cooling was invented in 1804 by British engineer Arthur Woolf, who patented his Woolf high pressure compound engine in 1805. In the compound engine, high pressure steam from the boiler expands in a high pressure (HP) cylinder and then enters one or more subsequent lower pressure (LP) cylinders. The complete expansion of the steam now occurs across multiple cylinders and as less expansion now occurs in each cylinder less heat is lost by the steam in each. This reduces the magnitude of cylinder heating and cooling, increasing the efficiency of the engine. To derive equal work from lower pressure steam requires a larger cylinder volume as this steam occupies a greater volume. Therefore the bore, and often the stroke, are increased in low pressure cylinders resulting in larger cylinders.

Double expansion (usually known as compound) engines expanded the steam in two stages. The pairs may be duplicated or the work of the large low pressure cylinder can be split with one high pressure cylinder exhausting into one or the other, giving a 3-cylinder layout where cylinder and piston diameter are about the same making the reciprocating masses easier to balance.

Two-cylinder compounds can be arranged as:

• Cross compounds - The cylinders are side by side.
• Tandem compounds - The cylinders are end to end, driving a common connecting rod
• Angle compounds - The cylinders are arranged in a vee (usually at a 90° angle) and drive a common crank.

With two-cylinder compounds used in railway work, the pistons are connected to the cranks as with a two-cylinder simple at 90° out of phase with each other (quartered). When the double expansion group is duplicated, producing a 4-cylinder compound, the individual pistons within the group are usually balanced at 180°, the groups being set at 90° to each other. In one case (the first type of Vauclain compound), the pistons worked in the same phase driving a common crosshead and crank, again set at 90° as for a two-cylinder engine. With the 3-cylinder compound arrangement, the LP cranks were either set at 90° with the HP one at 135° to the other two, or in some cases all three cranks were set at 120°.

The adoption of compounding was common for industrial units, for road engines and almost universal for marine engines after 1880; it was not universally popular in railway locomotives where it was often perceived as complicated. This is partly due to the harsh railway operating environment and limited space afforded by the loading gauge (particularly in Britain, where compounding was never common and not employed after 1930). However, although never in the majority, it was popular in many other countries.^[15]

[edit] Multiple expansion engines

An animation of a simplified triple-expansion engine.
High-pressure steam (red) enters from the boiler and passes through the engine, exhausting as low-pressure steam (blue), usually to a condenser.

It is a logical extension of the compound engine (described above) to split the expansion into yet more stages to increase efficiency. The result is the multiple expansion engine. Such engines use either three or four expansion stages and are known as triple and quadruple expansion engines respectively. These engines use a series of double-acting cylinders of progressively increasing diameter and/or stroke and hence volume. These cylinders are designed to divide the work into three or four, as appropriate, equal portions for each expansion stage. As with the double expansion engine, where space is at a premium, two smaller cylinders of a large sum volume may be used for the low pressure stage. Multiple expansion engines typically had the cylinders arranged inline, but various other formations were used. In the late 19th century, the Yarrow-Schlick-Tweedy balancing 'system' was used on some marine triple expansion engines. Y-S-T engines divided the low pressure expansion stages between two cylinders, one at each end of the engine. This allowed the crankshaft to be better balanced, resulting in a smoother, faster-responding engine which ran with less vibration. This made the 4-cylinder triple-expansion engine popular with large passenger liners (such as the Olympic class), but was ultimately replaced by the virtually vibration-free turbine (see below).

The image to the right shows an animation of a triple expansion engine. The steam travels through the engine from left to right. The valve chest for each of the cylinders is to the left of the corresponding cylinder.

Land-based steam engines could exhaust much of their steam, as feed water was usually readily available. Prior to and during World War I, the expansion engine dominated marine applications where high vessel speed was not essential. It was however superseded by the British invention steam turbine where speed was required, for instance in warships, such as the dreadnought battleships, and ocean liners. HMS Dreadnought of 1905 was the first major warship to replace the proven technology of the reciprocating engine with the then-novel steam turbine.

Uniflow (or unaflow) engine[link]

Schematic animation of a uniflow steam engine.
The poppet valves are controlled by the rotating camshaft at the top. High pressure steam enters, red, and exhausts, yellow.

Uniflow engines attempt to remedy the difficulties arising from the usual counterflow cycle where, during each stroke, the port and the cylinder walls will be cooled by the passing exhaust steam, whilst the hotter incoming admission steam will waste some of its energy in restoring working temperature. The aim of the uniflow is to remedy this defect and improve efficiency by providing an additional port uncovered by the piston at the end of each stroke making the steam flow only in one direction. By this means, the simple-expansion uniflow engine gives efficiency equivalent to that of classic compound systems with the added advantage of superior part-load performance, and comparable efficiency to turbines for smaller engines below one thousand horsepower. However, the thermal expansion gradient uniflow engines produce along the cylinder wall gives practical difficulties.

Rotary steam engines[link]

It is possible to use a mechanism based on a pistonless rotary engine such as the Wankel engine in place of the cylinders and valve gear of a conventional reciprocating steam engine. Many such engines have been designed, from the time of James Watt to the present day, but relatively few were actually built and even fewer went into quantity production; see link at bottom of article for more details. The major problem is the difficulty of sealing the rotors to make them steam-tight in the face of wear and thermal expansion; the resulting leakage made them very inefficient. Lack of expansive working, or any means of control of the cutoff is also a serious problem with many such designs. By the 1840s, it was clear that the concept had inherent problems and rotary engines were treated with some derision in the technical press. However, the arrival of electricity on the scene, and the obvious advantages of driving a dynamo directly from a high-speed engine, led to something of a revival in interest in the 1880s and 1890s, and a few designs had some limited success.

Of the few designs that were manufactured in quantity, those of the Hult Brothers Rotary Steam Engine Company of Stockholm, Sweden, and the spherical engine of Beauchamp Tower are notable. Tower's engines were used by the Great Eastern Railway to drive lighting dynamos on their locomotives, and by the Admiralty for driving dynamos on board the ships of the Royal Navy. They were eventually replaced in these niche applications by steam turbines.

Turbine engines[link]

A rotor of a modern steam turbine, used in a power plant

A steam turbine consists of one or more rotors (rotating discs) mounted on a drive shaft, alternating with a series of stators (static discs) fixed to the turbine casing. The rotors have a propeller-like arrangement of blades at the outer edge. Steam acts upon these blades, producing rotary motion. The stator consists of a similar, but fixed, series of blades that serve to redirect the steam flow onto the next rotor stage. A steam turbine often exhausts into a surface condenser that provides a vacuum. The stages of a steam turbine are typically arranged to extract the maximum potential work from a specific velocity and pressure of steam, giving rise to a series of variably sized high and low pressure stages. Turbines are only effective if they rotate at very high speed, therefore they are usually connected to reduction gearing to drive another mechanism, such as a ship's propeller, at a lower speed. This gearbox can be mechanical but today it is more common to use an alternator/generator set to produce electricity that later is used to drive an electric motor. A turbine rotor is also only capable of providing power when rotating in one direction. Therefore a reversing stage or gearbox is usually required where power is required in the opposite direction.

Steam turbines provide direct rotational force and therefore do not require a linkage mechanism to convert reciprocating to rotary motion. Thus, they produce smoother rotational forces on the output shaft. This contributes to a lower maintenance requirement and less wear on the machinery they power than a comparable reciprocating engine.

The Turbinia – the first steam turbine-powered ship

The main use for steam turbines is in electricity generation (about 90% of the world's electric production is by use of steam turbines)^[2] and to a lesser extent as marine prime movers. In the former, the high speed of rotation is an advantage, and in both cases the relative bulk is not a disadvantage; in the latter (pioneered on the Turbinia), the light weight, high efficiency and high power are highly desirable.

Virtually all nuclear power plants generate electricity by heating water to provide steam that drives a turbine connected to an electrical generator. Nuclear-powered ships and submarines either use a steam turbine directly for main propulsion, with generators providing auxiliary power, or else employ turbo-electric propulsion, where the steam drives a turbine-generator set with propulsion provided by electric motors. A limited number of steam turbine railroad locomotives were manufactured. Some non-condensing direct-drive locomotives did meet with some success for long haul freight operations in Sweden and for express passenger work in Britain, but were not repeated. Elsewhere, notably in the U.S.A., more advanced designs with electric transmission were built experimentally, but not reproduced. It was found that steam turbines were not ideally suited to the railroad environment and these locomotives failed to oust the classic reciprocating steam unit in the way that modern diesel and electric traction has done.

Rocket type[link]

The aeolipile represents the use of steam by the rocket-reaction principle, although not for direct propulsion.

In more modern times there has been limited use of steam for rocketry – particularly for rocket cars. The technique is simple in concept, simply fill a pressure vessel with hot water at high pressure, and open a valve leading to a suitable nozzle. The drop in pressure immediately boils some of the water and the steam leaves through a nozzle, giving a significant propulsive force.

Cold sink[link]

A power station's cooling tower produces clouds from the low temperature waste-heat which has been transferred to air which rises and cools

As with all heat engines, a considerable quantity of waste heat at relatively low temperature is produced and must be disposed of.

The simplest cold sink is to vent the steam to the environment. This is often used on steam locomotives, as the released steam is released in the chimney so as to increase the draw on the fire, which greatly increases engine power, but is inefficient. Condensing steam locomotives have been built, but only for special applications such as working in tunnels.

Sometimes the waste heat is useful in and of itself, and in those cases very high overall efficiency can be obtained. For example, combined heat and power (CHP) systems use the waste steam for district heating.

Where CHP is not used, steam turbines in power stations use surface condensers as a cold sink. The condensers are cooled by water flow from oceans, rivers, lakes, and often by cooling towers which evaporate water to provide cooling energy removal. The resulting condensed hot water output from the condenser is then put back into the boiler via a pump. The water vapour with entrained droplets often seen billowing from power stations is generated by the cooling systems (not from the closed-loop Rankine power cycle) and represents the waste energy heat (pumping and vaporization) that could not be converted to useful work in the turbine. Note that cooling towers operate using the latent heat of vaporization of the cooling fluid. The white billowing clouds that form in cooling tower operation are the result of water droplets in the atmosphere that become entrained in the cooling tower airflow; they are not, as commonly thought, released steam.

Water pump[link]

An injector uses a jet of steam to force water into the boiler.

The Rankine cycle and most practical steam engines have a water pump to recycle or top up the boiler water, so that they may be run continuously. The water pump can be of almost any type although special types, such as an injector, which is a pump that uses a steam jet usually supplied from the boiler and is present on many steam locomotives.

Monitoring equipment[link]

Richard's indicator instrument of 1875. See: Indicator diagram (above)

For safety reasons, nearly all steam engines are equipped with mechanisms to monitor the boiler, such as a pressure gauge and a sight glass to monitor the water level.

Many engines, stationary and mobile, are also fitted with a governor to regulate the speed of the engine without the need for human interference (similar to cruise control in some cars).

The most useful instrument for analyzing the performance of steam engines is the steam engine indicator. Early versions were in use by 1851,^[18] but the most successful indicator was developed for the high speed engine inventor and manufacturer Charles Porter by Charles Richard and exhibited at London Exhibition in 1862.^[12] The steam engine indicator traces on paper the pressure in the cylinder throughout the cycle, which can be used to spot various problems and calculate developed horsepower.^[19] It was routinely used by engineers, mechanics and insurance inspectors. The engine indicator can also be used on internal combustion engines. See image of indicator diagram above.

Advantages[link]

The strength of the steam engine for modern purposes is in its ability to convert heat from almost any source into mechanical work, unlike the internal combustion engine.

Similar advantages are found in a different type of external combustion engine, the Stirling engine, which can offer efficient power (with advanced regenerators and large radiators) at the cost of a much lower power-to-size/weight ratio than even modern steam engines with compact boilers^{[citation needed]}. These Stirling engines are not commercially produced, although the concepts are promising.

Steam locomotives are especially advantageous at high elevations as they are not adversely affected by the lower atmospheric pressure. This was inadvertently discovered when steam locomotives operated at high altitudes in the mountains of South America were replaced by diesel-electric units of equivalent sea level power. These were quickly replaced by much more powerful locomotives capable of producing sufficient power at high altitude.

For road vehicles, steam propulsion has the advantage of having high torque from stationary, removing the need for a clutch and transmission, though start-up time and sufficiently compact packaging remain a problem.

In Switzerland (Brienz Rothhorn) and Austria (Schafberg Bahn) new rack steam locomotives have proved very successful. They were designed based on a 1930s design of Swiss Locomotive and Machine Works (SLM) but with all of today's possible improvements like roller bearings, heat insulation, light-oil firing, improved inner streamlining, one-man-driving and so on. These resulted in 60 percent lower fuel consumption per passenger^{[citation needed]} and massively reduced costs for maintenance and handling^{[citation needed]}. Economics now are similar or better than with most advanced diesel or electric systems. Also a steam train with similar speed and capacity is 50 percent lighter than an electric or diesel train^{[citation needed]}, thus, especially on rack railways, significantly reducing wear and tear on the track. Also, a new steam engine for a paddle steam ship on Lake Geneva, the Montreux, was designed and built, being the world's first full-size ship steam engine with an electronic remote control.^[20] The steam group of SLM in 2000 created a wholly owned company called DLM to design modern steam engines and steam locomotives.

Safety[link]

Steam engines possess boilers and other components that are pressure vessels that contain a great deal of potential energy. Steam escapes and boiler explosions (typically BLEVEs) can and have caused great loss of life in the past. While variations in standards may exist in different countries, stringent legal, testing, training, care with manufacture, operation and certification is applied to ensure safety.

Failure modes may include:

• over-pressurisation of the boiler
• insufficient water in the boiler causing overheating and vessel failure
• build up of sediment and scale which caused local hot spots, especially in riverboats using feed dirty water
• pressure vessel failure of the boiler due to inadequate construction or maintenance.
• escape of steam from pipework/boiler causing scalding

Steam engines frequently possess two independent mechanisms for ensuring that the pressure in the boiler does not go too high; one may be adjusted by the user, the second is typically designed as an ultimate fail-safe. Such safety valves normally use a simple lever to activate a stopcock in the upper side of a boiler. One end of the lever is attached to the stopcock while the other has a weight attached and its position can be adjusted to change the pressure at which stem will be released automatically by the stopcock.

Lead fusible plugs may be present in the crown of the firebox. If the water level drops, such that the temperature of the firebox crown increases significantly, the lead melts and the steam escapes, warning the operators, who may then manually drop the fire. Except in the smallest of boilers the steam escape has little effect on dampening the fire. The plugs are also too small in area to lower steam pressure significantly, depressurizing the boiler. If they were any larger, the volume of escaping steam would itself endanger the crew.

Efficiency[link]

See also: Engine efficiency#Steam engine

The efficiency of an engine can be calculated by dividing the energy output of mechanical work that the engine produces by the energy input to the engine by the burning fuel.

The historical measure of a steam engine's energy efficiency was its "duty". The concept of duty was first introduced by Watt in order to illustrate how much more efficient his engines were over the earlier Newcomen designs. Duty is the number of foot-pounds of work delivered by burning one bushel (94 pounds) of coal. The best examples of Newcomen designs had a duty of about 7 million, but most were closer to 5 million. Watt's original low-pressure designs were able to deliver duty as high as 25 million, but averaged about 17. This was a three-fold improvement over the average Newcomen design. Early Watt engines equipped with high-pressure steam improved this to 65 million.^[21]

No heat engine can be more efficient than the Carnot cycle, in which heat is moved from a high temperature reservoir to one at a low temperature, and the efficiency depends on the temperature difference. For the greatest efficiency, steam engines should be operated at the highest steam temperature possible (superheated steam), and release the waste heat at the lowest temperature possible.

The efficiency of a Rankine cycle is usually limited by the working fluid. Without the pressure reaching super critical levels for the working fluid, the temperature range the cycle can operate over is quite small; in steam turbines, turbine entry temperatures are typically 565°C (the creep limit of stainless steel) and condenser temperatures are around 30°C. This gives a theoretical Carnot efficiency of about 63% compared with an actual efficiency of 42% for a modern coal-fired power station. This low turbine entry temperature (compared with a gas turbine) is why the Rankine cycle is often used as a bottoming cycle in combined-cycle gas turbine power stations.

One of the principal advantages the Rankine cycle holds over others is that during the compression stage relatively little work is required to drive the pump, the working fluid being in its liquid phase at this point. By condensing the fluid, the work required by the pump consumes only 1% to 3% of the turbine power and contributes to a much higher efficiency for a real cycle. The benefit of this is lost somewhat due to the lower heat addition temperature. Gas turbines, for instance, have turbine entry temperatures approaching 1500°C. Nonetheless, the efficiencies of actual large steam cycles and large modern gas turbines are fairly well matched.

In practice, a steam engine exhausting the steam to atmosphere will typically have an efficiency (including the boiler) in the range of 1-10%, but with the addition of a condenser and multiple expansion, it may be greatly improved to 25% or better.

A modern large electrical power station (producing several hundred megawatts of electrical output) with steam reheat, economizer etc. will achieve efficiency in the mid 40% range, with the most efficient units approaching 50% thermal efficiency.^[22]

It is also possible to capture the waste heat using cogeneration in which the waste heat is used for heating a lower boiling point working fluid or as a heat source for district heating via saturated low pressure steam. By this means it is possible to use as much as 85-90% of the input energy.

Applications[link]

Since the early 18th century, steam power has been applied to a variety of practical uses. At first it was applied to reciprocating pumps, but from the 1780s rotative engines (i.e. those converting reciprocating motion into rotary motion) began to appear, driving factory machinery such as spinning mules and power looms. At the turn of the 19th century, steam-powered transport on both sea and land began to make its appearance becoming ever more dominant as the century progressed.

Steam engines can be said to have been the moving force behind the Industrial Revolution and saw widespread commercial use driving machinery in factories, mills and mines; powering pumping stations; and propelling transport appliances such as railway locomotives, ships and road vehicles. Their use in agriculture led to an increase in the land available for cultivation.

Very low power engines are used to power models and toys, and speciality applications such as the steam clock.

The presence of several phases between heat source and power delivery has meant that it has always been difficult to obtain a power-to-weight ratio anywhere near that obtainable from internal combustion engines; notably this has made steam aircraft extremely rare. Similar considerations have meant that for small and medium-scale applications steam has been largely superseded by internal combustion engines or electric motors, which has given the steam engine an out-dated image. However it is important to remember that the power supplied to the electric grid is predominantly generated using steam turbine plant, so that indirectly the world's industry is still dependent on steam power. Recent concerns about fuel sources and pollution have incited a renewed interest in steam both as a component of cogeneration processes and as a prime mover. This is becoming known as the Advanced Steam movement.

Steam engines can be classified by their application:

Stationary applications[link]

Stationary steam engines can be classified into two main types:

1. Winding engines, rolling mill engines, steam donkeys, marine engines, and similar applications which need to frequently stop and reverse.
2. Engines providing power, which rarely stop and do not need to reverse. These include engines used in thermal power stations and those that were used in pumping stations, mills, factories and to power cable railways and cable tramways before the widespread use of electric power.

The steam donkey is technically a stationary engine but is mounted on skids to be semi-portable. It is designed for logging use and can drag itself to a new location. Having secured the winch cable to a sturdy tree at the desired destination, the machine will move towards the anchor point as the cable is winched in.

A portable engine is a stationary engine mounted on wheels so that it may be towed to a work-site by horses or a traction engine, rather than being fixed in a single location.

Transport applications[link]

A steam locomotive – a GNR N2 Class No.1744 at Weybourne nr. Sheringham, Norfolk

A steam-powered bicycle

Steam engines have been used to power a wide array of transport appliances:

• Marine: Steamboat, steamship, steam yacht
• Rail: Steam locomotive, fireless locomotive
• Agriculture: Traction engine, steam tractor
• Road: Steam wagon, steam bus, steam tricycle, steam car
• Construction: Steam roller, steam shovel
• Military: steam tank (tracked), steam tank (wheeled), steam catapult
• Space: Steam rocket

In these applications internal combustion engines are now used due to their higher power-to-weight ratio, lower maintenance and space requirements .

Modern applications[link]

Although the reciprocating steam engine is no longer in widespread commercial use, various companies are exploring or exploiting the potential of the engine as an alternative to internal combustion engines.

The company Energiprojekt AB in Sweden has made progress in using modern materials for harnessing the power of steam. The efficiency of Energiprojekt's steam engine reaches some 27-30% on high-pressure engines. It is a single-step, 5-cylinder engine (no compound) with superheated steam and consumes approx. 4 kg (8.8 lb) of steam per kWh.^[23]

See also[link]

References[link]

Further reading[link]

• Crump, Thomas. A Brief History of the Age of Steam: From the First Engine to the Boats and Railways (2007)
• Hunter, Louis C. (1985). A History of Industrial Power in the United States, 1730-1930, Vol. 2: Steam Power. Charolttesville: University Press of Virginia. 
• Marsden, Ben. Watt's Perfect Engine: Steam and the Age of Invention (Columbia University Press, 2004)
• Robinson, Eric H. "The Early Diffusion of Steam Power" Journal of Economic History Vol. 34, No. 1, (March 1974), pp. 91–107
• Rose, Joshua. Modern Steam Engines (1887, reprint 2003)
• Stuart, Robert, A Descriptive History of the Steam Engine (London: J. Knight and H. Lacey, 1824.)
• Van Riemsdijk, J. T. Pictorial History of Steam Power (1980)
• Steam-its generation and use. Babcock & Wilcox. (Numerous editions).  An engineering handbook widely used by those involved with various types of boilers. Contains numerous illustrations, graphs and useful formulas. Contains a history of the steam engine.

External links[link]

Wikimedia Commons has media related to: Steam engines

Look up steam engine in Wiktionary, the free dictionary.

• A history of growth of the steam engine
• Animated engines - Illustrates a variety of steam engines
• Howstuffworks - "How Steam Engines Work"

Steam phase eruption of Castle Geyser in Yellowstone Park A temperature-versus-entropy diagram for steam A Mollier enthalpy-versus-entropy diagram for steam

Steam is the technical term for water vapor, the gaseous phase of water, which is formed when water boils. In common language it is often used to refer to the visible mist of water droplets formed as this water vapor condenses in the presence of cooler air. At lower pressures, such as in the upper atmosphere or at the top of high mountains water boils at a lower temperature than the nominal 100 °C (212 °F) at standard temperature and pressure. If heated further it becomes superheated steam.

The enthalpy of vaporization is the energy required to turn water into the gaseous form when it increases in volume by 1,600 times at standard temperature and pressure; this change in volume can be converted into mechanical work by steam engines and steam turbines. Steam engines played a central role to the Industrial Revolution and modern steam turbines are used to generate electricity. If liquid water comes in contact with a very hot substance (such as lava, or molten metal) it can create a steam explosion. Steam explosions have been responsible for many foundry accidents and may also have been responsible for much of the damage to the plant in the Chernobyl accident.

Types of steam and conversion[link]

Water vapor that includes water droplets is described as wet steam. As wet steam is heated further, the droplets evaporate, and at a high enough temperature (which depends on the pressure) all of the water evaporates and the system is in vapor-liquid equilibrium.^[1]

Superheated steam is steam at a temperature higher than its boiling point for the pressure which only occurs where all the water has evaporated or has been removed from the system.^[2]

Steam tables contain thermodynamic data for water/steam and are often used by engineers and scientists in design and operation of equipment where thermodynamic cycles involving steam are used. Additionally, thermodynamic phase diagrams for water/steam, such as a temperature-entropy diagram or a Mollier diagram shown in this article, may be useful. Steam charts are also used for analysing thermodynamic cycles.

enthalpy-entropy (h-s) diagram for steam	pressure-enthalpy (p-h) diagram for steam	temperature-entropy (T-s) diagram for steam

Uses[link]

Agricultural[link]

In agriculture, steam is used for soil sterilization to avoid the use of harmful chemical agents and increase soil health.

Domestic[link]

Steam's capacity to transfer heat is also used in the home: for cooking vegetables, steam cleaning of fabric and carpets, and heating buildings. In each case, water is heated in a boiler, and the steam carries the energy to a target object. "Steam showers" are actually low-temperature mist-generators, and do not actually use steam.

Electricity generation (and cogeneration)[link]

About 90% of all electricity is generated using steam as the working fluid, nearly all by steam turbines.^[3]

In electric generation, steam is typically condensed at the end of its expansion cycle, and returned to the boiler for re-use. However in cogeneration, steam is piped into buildings through a district heating system to provide heat energy after its use in the electric generation cycle. The world's biggest steam generation system is the New York City steam system which pumps steam into 100,000 buildings in Manhattan from seven cogeneration plants.^[4]

Energy storage[link]

Fireless steam locomotive
Despite the resemblance to a boiler, note the lack of a chimney and also how the cylinders are at the cab end, not the chimney end.

In other industrial applications steam is used for energy storage, which is introduced and extracted by heat transfer, usually through pipes. Steam is a capacious reservoir for thermal energy because of water's high heat of vaporization.

Fireless steam locomotives were steam locomotives that operated from a supply of steam stored on-board in a large tank resembling a conventional locomotive's boiler. This tank was filled by process steam, as is available in many sorts of large factory, such as paper mills. The locomotive's propulsion used pistons and connecting rods, as for a typical steam locomotive. These locomotives were mostly used in places where there was a risk of fire from a boiler's firebox, but were also used in factories that simply had a plentiful supply of steam to spare.

Lifting gas[link]

Owing to its low molecular mass, steam is an effective lifting gas, providing approximately 60% as much lift as helium and twice as much as hot air. It is not flammable, unlike hydrogen, and is cheap and abundant, unlike helium. The required heat, however, leads to condensation problems and requires an insulated envelope. These factors have limited its use thus far to mostly demonstration projects.^[5]

Mechanical effort[link]

A steam engine and steam turbines use the expansion of steam to drive a piston or turbine to perform mechanical work. The ability to return condensed steam as water-liquid to the boiler at high pressure with relatively little expenditure of pumping power is important. Condensation of steam to water often occurs at the low-pressure end of a steam turbine, since this maximizes the energy efficiency, but such wet-steam conditions have to be limited to avoid excessive turbine blade erosion. Engineers use an idealised thermodynamic cycle, the Rankine cycle, to model the behavior of steam engines. Steam turbines are often used in the production of electricity.

Sterilization[link]

An autoclave, which uses steam under pressure, is used in microbiology laboratories and similar environments for sterilization.

Steam in piping[link]

Steam is used in piping for utility lines. It is also used in jacketing and tracing of piping to maintain the uniform temperature in pipelines and vessels.

Wood treatment[link]

Steam is used in the process of wood bending, killing insects and increasing plasticity.

Concrete treatment[link]

Steam is used to accentuate drying especially in prefabricates.

Cleaning[link]

Used in cleaning of fibers, sometimes prior to painting.

See also[link]

Look up steam in Wiktionary, the free dictionary.

Wikimedia Commons has media related to: Steam

Wikimedia Commons has media related to: Water vapor

• Electrification
• Food steamer or steam cooker
• Geyser—geothermally-generated steam
• IAPWS—an association that maintains international-standard correlations for the thermodynamic properties of steam, including IAPWS-IF97 (for use in industrial simulation and modelling) and IAPWS-95 (a general purpose and scientific correlation).
• Industrial Revolution
• Live steam
• Mass production
• Nuclear power—and power plants use steam to generate electricity
• Oxyhydrogen
• Psychrometrics—moist air/vapor mixtures, humidity and air conditioning
• Steam locomotive

References[link]

External links[link]

• Steam Tables & Charts by National Institute of Standards and Technology, NIST
• What Is Steam? (general article about the properties of water/steam)
• Steam Tracing
• Online steam properties calculator (Spirax Sarco)
• Free Steam Tables Online calculator based on IAPWS-IF97 (MegaWatSoft)
• Online Steam Tables Calculator based on IFC-67
• freesteam a free (GPL) library for calculation of steam properties using the IAPWS-IF97 standard.
• JSteam A Windows library and free calculator for the calculation of steam properties using the IAPWS-IF97-07 standards.
• JSteam Excel Add In An Excel add in for modelling and solving steam utility systems using the JSteam library.

James Watt
Portrait of James Watt (1736-1819) by Carl Frederik von Breda
Born	(1736-01-19)19 January 1736 Greenock, Renfrewshire, Scotland
Died	25 August 1819(1819-08-25) (aged 83)[1] Handsworth, Birmingham, England
Residence	Glasgow then Handsworth, Great Britain
Citizenship	Kingdom of Great Britain
Nationality	Scottish
Fields	Inventor and Mechanical Engineer
Institutions	University of Glasgow Boulton and Watt
Known for	Improving the steam engine
Signature

James Watt, FRS, FRSE (19 January 1736 – 25 August 1819)^[1] was a Scottish inventor and mechanical engineer whose improvements to the Newcomen steam engine were fundamental to the changes brought by the Industrial Revolution in both his native Great Britain and the rest of the world.

While working as an instrument maker at the University of Glasgow, Watt became interested in the technology of steam engines. He realised that contemporary engine designs wasted a great deal of energy by repeatedly cooling and re-heating the cylinder. Watt introduced a design enhancement, the separate condenser, which avoided this waste of energy and radically improved the power, efficiency, and cost-effectiveness of steam engines. Eventually he adapted his engine to produce rotary motion, greatly broadening its use beyond pumping water.

Watt attempted to commercialize his invention, but experienced great financial difficulties until 1775 he entered a partnership with Matthew Boulton. The new firm of Boulton and Watt was eventually highly successful and Watt became a wealthy man. In his retirement, Watt continued to develop new inventions though none were as significant as his steam engine work. He died in 1819 at the age of 83. Watt has been described as one of the most influential figures in human history.^[2]

He developed the concept of horsepower^[3] and the SI unit of power, the watt, was named after him.

Biography[link]

James Watt was born on 19 January 1736 in Greenock, Renfrewshire, a seaport on the Firth of Clyde.^[4] His father was a shipwright, ship owner and contractor, and served as the town's chief baillie,^[5] while his mother, Agnes Muirhead, came from a distinguished family and was well educated. Both were Presbyterians and strong Covenanters.^[6] Watt's grandfather, Thomas Watt, was a mathematics teacher and baillie to the Baron of Cartsburn.^[7]

Watt did not attend school regularly; initially he was mostly schooled at home by his mother but later he attended Greenock grammar school.^[8] He exhibited great manual dexterity, engineering skills and an aptitude for mathematics, while Latin and Greek failed to interest him.

When he was eighteen, his mother died and his father's health began to fail. Watt travelled to London to study instrument-making for a year, then returned to Scotland, settling in the major commercial city of Glasgow intent on setting up his own instrument-making business. He made and repaired brass reflecting quadrants, parallel rulers, scales, parts for telescopes, and barometers, among other things. Because he had not served at least seven years as an apprentice, the Glasgow Guild of Hammermen (which had jurisdiction over any artisans using hammers) blocked his application,^[9] despite there being no other mathematical instrument makers in Scotland.^[10]

Watt was saved from this impasse by the arrival of astronomical instruments to the University of Glasgow that required expert attention.^[11] Watt restored them to working order and was remunerated. These instruments were eventually installed in the Macfarlane Observatory. Subsequently three professors offered him the opportunity to set up a small workshop within the university. It was initiated in 1757 and one of the professors, the physicist and chemist Joseph Black, became Watt's friend.^[12]

At first he worked on maintaining and repairing scientific instruments used in the university, helping with demonstrations, and expanding the production of quadrants. In 1759 he formed a partnership with John Craig, an architect and businessman, to manufacture and sell a line of products including musical instruments and toys. This partnership lasted for the next six years, and employed up to sixteen workers. Craig died in 1765. One employee, Alex Gardner, eventually took over the business, which lasted into the twentieth century.^[13]

In 1764, Watt married his cousin Margaret (Peggy) Miller, with whom he had five children, two of whom lived to adulthood: James Jr. (1769–1848) and Margaret (1767–1796). His wife died in childbirth in 1772. In 1777 he married again, to Ann MacGregor, daughter of a Glasgow dye-maker, with whom he had two children: Gregory (1777–1804), who became a geologist and mineralogist,^[14] and Janet (1779–1794). Ann died in 1832. Between 1777 and 1790 he lived in Regent Place, Birmingham^[15]

Early experiments with steam[link]

Original condenser by Watt (Science Museum (London))

In 1759 Watt's friend, John Robison, called his attention to the use of steam as a source of motive power.^[16] The design of the Newcomen engine, in use for almost 50 years for pumping water from mines, had hardly changed from its first implementation. Watt began to experiment with steam though he had never seen an operating steam engine. He tried constructing a model. It failed to work satisfactorily, but he continued his experiments and began to read everything he could about the subject. He came to realize the importance of latent heat in understanding the engine, which, unknown to Watt, his friend, Joseph Black, had previously discovered some years before. Understanding of the steam engine was in a very primitive state, for the science of thermodynamics was not in place for another 100 years or so.

In 1763, Watt was asked to repair a model Newcomen engine belonging to the University.^[16] Even after repair, this engine only barely worked. After much experimentation, Watt demonstrated that about three quarters of the heat of the steam was being wasted - consumed in heating the engine cylinder on every cycle.^[17] This energy was wasted because later in the cycle, cold water was injected into the cylinder to condense the steam to reduce its pressure. Thus the engine expended much of its energy in repeatedly heating the cylinder rather than in delivering mechanical force.

Watt's critical insight, arrived at in May 1765,^[18] was to cause the steam to condense in a separate chamber apart from the piston, and to maintain the temperature of the cylinder at the same temperature as the injected steam (by surrounding it with a "steam jacket").^[17] This meant that very little heat was absorbed into the cylinder itself on each cycle, and thus more heat from the steam was made available to perform useful work. Watt had a working model later that same year.

The ruin of Watt's cottage workshop at Kinneil House

Cylinder fragment of Watt's first operational engine at the Carron Works, Falkirk

Despite a potentially workable design, there were still substantial difficulties in constructing a full-scale engine. This required more capital, some of which came from Black. More substantial backing came from John Roebuck, the founder of the celebrated Carron Iron Works, near Falkirk, with whom he now formed a partnership. Roebuck lived at Kinneil House in Bo'ness, during which time Watt worked at perfecting his steam engine, in a cottage adjacent to the house. The shell of the cottage, and a very large part of one of his projects, still exist to the rear.^[19]

The principal difficulty was in machining the piston and cylinder. Iron workers of the day were more like blacksmiths than modern machinists and were unable to produce the components with sufficient precision. Much capital was spent in pursuing the ground-breaking patent on Watt's invention. Strapped for resources, Watt was forced to take up employment first as a surveyor, then as a Civil engineer for eight years.^[20]

Roebuck went bankrupt, and Matthew Boulton, who owned the Soho Foundry works near Birmingham, acquired his patent rights. An extension of the patent to 1800 was successfully obtained in 1775.^[21]

Through Boulton, Watt finally had access to some of the best iron workers in the world. The difficulty of the manufacture of a large cylinder with a tightly fitting piston was solved by John Wilkinson who had developed precision boring techniques for cannon making at Bersham, near Wrexham, North Wales. Watt and Boulton formed a hugely successful partnership (Boulton and Watt), which lasted for the next twenty-five years.

First engines[link]

Engraving of a 1784 steam engine designed by Boulton and Watt.

In 1776, the first engines were installed and working in commercial enterprises. These first engines were used to power pumps and produced only reciprocating motion to move the pump rods at the bottom of the shaft. The design was commercially successful, and for the next five years Watt was very busy installing more engines, mostly in Cornwall for pumping water out of mines.

These early engines were not manufactured by Boulton and Watt, but were made by others according to drawings made by Watt, who served in the role of consulting engineer. The erection of the engine and its shakedown was supervised by Watt, at first, and then by men in the firm's employ. These were large machines. The first, for example, had a cylinder with a diameter of some 50 inches and an overall height of about 24 feet, and required the construction of a dedicated building to house it. Boulton and Watt charged an annual payment, equal to one third of the value of the coal saved in comparison to a Newcomen engine performing the same work.

The field of application for the invention was greatly widened when Boulton urged Watt to convert the reciprocating motion of the piston to produce rotational power for grinding, weaving and milling. Although a crank seemed the obvious solution to the conversion Watt and Boulton were stymied by a patent for this, whose holder, James Pickard, and associates proposed to cross-license the external condenser. Watt adamantly opposed this and they circumvented the patent by their sun and planet gear in 1781.

Over the next six years, he made a number of other improvements and modifications to the steam engine. A double acting engine, in which the steam acted alternately on the two sides of the piston was one. He described methods for working the steam "expansively" (i.e., using steam at pressures well above atmospheric). A compound engine, which connected two or more engines was described. Two more patents were granted for these in 1781 and 1782. Numerous other improvements that made for easier manufacture and installation were continually implemented. One of these included the use of the steam indicator which produced an informative plot of the pressure in the cylinder against its volume, which he kept as a trade secret. Another important invention, one which Watt was most proud of, was the Parallel motion which was essential in double-acting engines as it produced the straight line motion required for the cylinder rod and pump, from the connected rocking beam, whose end moves in a circular arc. This was patented in 1784. A throttle valve to control the power of the engine, and a centrifugal governor, patented in 1788,^[22] to keep it from "running away" were very important. These improvements taken together produced an engine which was up to five times as efficient in its use of fuel as the Newcomen engine.

Because of the danger of exploding boilers, which were in a very primitive stage of development, and the ongoing issues with leaks, Watt restricted his use of high pressure steam – all of his engines used steam at near atmospheric pressure.

Patent trials[link]

A steam engine built to James Watt's patent in 1848 at Freiberg in Germany

Edward Bull started constructing engines for Boulton and Watt in Cornwall in 1781. By 1792 he had started making engines of his own design, but which contained a separate condenser, and so infringed Watt's patents. Two brothers, Jabez Carter Hornblower and Jonathan Hornblower Jnr also started to build engines about the same time. Others began to modify Newcomen engines by adding a condenser, and the mine owners in Cornwall became convinced that Watt's patent could not be enforced. They started to withhold payments due to Boulton and Watt, which by 1795 had fallen. Of the total £21,000 (£1,660,000 as of 2012) owed, only £2,500 had been received. Watt was forced to go to court to enforce his claims.^[23]

He first sued Bull in 1793. The jury found for Watt, but the question of whether or not the original specification of the patent was valid was left to another trial. In the meantime, injunctions were issued against the infringers, forcing their payments of the royalties to be placed in escrow. The trial on determining the validity of the specifications which was held in the following year was inconclusive, but the injunctions remained in force and the infringers, except for Jonathan Hornblower, all began to settle their cases. Hornblower was soon brought to trial and the verdict of the four judges (in 1799) was decisively in favour of Watt. Their friend John Wilkinson, who had solved the problem of boring an accurate cylinder, was a particularly grievous case. He had erected about twenty engines without Boulton's and Watts' knowledge. They finally agreed to settle the infringement in 1796.^[24] Boulton and Watt never collected all that was owed them, but the disputes were all settled directly between the parties or through arbitration. These trials were extremely costly in both money and time, but ultimately were successful for the firm.

Copying machine[link]

Before 1780 there was no good method for making copies of letters or drawings. The only method sometimes used was a mechanical one using linked multiple pens. Watt at first experimented with improving this method, but soon gave up on this approach because it was so cumbersome. He instead decided to try to physically transfer some ink from the original to another sheet of paper which was thin enough for the ink to go through to the other side, thus reproducing the writing exactly.^[25]

Watt started to develop the process in 1779, and made many experiments to formulate the ink, select the thin paper, to devise a method for wetting the special thin paper, and to make a press suitable for applying the correct pressure to effect the transfer. All of these required much experimentation, but he soon had enough success to patent the process a year later. Watt formed another partnership with Boulton (who provided financing) and James Keir (to manage the business) in a firm called James Watt and Co. The perfection of the invention required much more development work before it could be routinely used by others, but this was carried out over the next few years. Boulton and Watt gave up their shares to their sons in 1794.^[26] It became a commercial success and was widely used in offices even into the twentieth century.

Chemical experiments[link]

From an early age Watt was very interested in chemistry. In late 1786, while in Paris, he witnessed an experiment by Berthollet in which he reacted hydrochloric acid with manganese dioxide to produce chlorine. He had already found that an aqueous solution of chlorine could bleach textiles, and had published his findings, which aroused great interest among many potential rivals. When Watt returned to Britain, he began experiments along these lines with hopes of finding a commercially viable process. He discovered that a mixture of salt, manganese dioxide and sulfuric acid could produce chlorine, which Watt believed might be a cheaper method. He passed the chlorine into a weak solution of alkali, and obtained a turbid solution that appeared to have good bleaching properties. He soon communicated these results to James McGrigor, his father-in-law, who was a bleacher in Glasgow. Otherwise he tried to keep his method a secret.^[27]

With McGrigor, and his wife Annie, he started to scale up the process, and in March 1788, McGrigor was able to bleach 1500 yards of cloth to his satisfaction. About this time Berthollet discovered the salt and sulphuric acid process, and published it so it became public knowledge. Many others began to experiment with improving the process, which still had many shortcomings, not the least of which was the problem of transporting the liquid product. Watt's rivals soon overtook him in developing the process, and he dropped out of the race. It was not until 1799, when Charles Tennant patented a process for producing solid bleaching powder (calcium hypochlorite) that it became a commercial success.

By 1794 Watt had been chosen by Thomas Beddoes to manufacture apparatus to produce, clean and store gases for use in the new Pneumatic Institution at Hotwells in Bristol. Watt continued to experiment with various gases for several years, but by 1797 the medical uses for the "factitious airs" had come to a dead end.^[28]

Scientific apparatus designed by Boulton and Watt in preparation of the Pneumatic Institution in Bristol

Personality[link]

Watt combined theoretical knowledge of science with the ability to apply it practically. Humphry Davy said of him that "Those who consider James Watt only as a great practical mechanic form a very erroneous idea of his character; he was equally distinguished as a natural philosopher and a chemist, and his inventions demonstrate his profound knowledge of those sciences, and that peculiar characteristic of genius, the union of them for practical application".^[29]

He was greatly respected^[30] by other prominent men of the Industrial Revolution. He was an important member of the Lunar Society, and was a much sought-after conversationalist and companion, always interested in expanding his horizons.^[31] His personal relationships with his friends and partners were always congenial and long-lasting.

Watt was a prolific correspondent. During his years in Cornwall, he wrote long letters to Boulton several times per week. He was averse to publishing his results in, for example, the Philosophical Transactions of the Royal Society however, and instead preferred to communicate his ideas in patents.^[32] He was an excellent draughtsman.

He was a rather poor businessman, and especially hated bargaining and negotiating terms with those who sought to utilize the steam engine. In a letter to William Small in 1772, Watt confessed that "he would rather face a loaded cannon than settle an account or make a bargain."^[33] Until he retired, he was always much concerned about his financial affairs, and was something of a worrier. His health was often poor. He was subject to frequent nervous headaches and depression.

The Soho Foundry[link]

At first the partnership made the drawing and specifications for the engines, and supervised the work to erect it on the customers property. They produced almost none of the parts themselves. Watt did most of his work at his home in Harper’s Hill in Birmingham, while Boulton worked at the Soho Manufactory. Gradually the partners began to actually manufacture more and more of the parts, and by 1795 they purchased a property about a mile away from the Soho Manufactory, on the banks of the Birmingham Canal, to establish a new foundry for the manufacture of the engines. The Soho Foundry formally opened in 1796 at a time when Watt’s sons, Gregory and James Jr. were heavily involved in the management of the enterprise. In 1800, the year of Watt’s retirement, the firm made a total of 41 engines.^[34]

Later years[link]

"Heathfield", Watt's house in Handsworth, Birmingham

James Watt's workshop

Watt retired in 1800, the same year that his fundamental patent and partnership with Boulton expired. The famous partnership was transferred to the men's sons, Matthew Boulton and James Watt Jr. Longtime firm engineer William Murdoch was soon made a partner and the firm prospered.

Watt continued to invent other things before and during his semi-retirement. Within his home in Handsworth Heath, Staffordshire, Watt made use of a garret room as a workshop, and it was here that he worked on many of his inventions.^[35] Among other things, he invented and constructed several machines for copying sculptures and medallions which worked very well, but which he never patented.^[36] He maintained his interest in Civil Engineering and was a consultant on several significant projects. He proposed, for example, a method for constructing a flexible pipe to be used for passing water under the Clyde at Glasgow.^[37]

He and his second wife travelled to France and Germany, and he purchased an estate in Wales at Doldowlod House, one mile south of Llanwrthwl, which he much improved.

He died on 25 August 1819 at his home "Heathfield" in Handsworth, Birmingham, England at the age of 83. He was buried on 2 September.

Murdoch's contributions[link]

James Murdoch joined Boulton and Watt in 1777. At first he worked in the pattern shop in Soho, but soon he was erecting engines in Cornwall. He became an important part of the firm and made many contributions to its success. A very able man, he made several important inventions on his own.

John Griffiths, who wrote a biography^[38] of him in 1992, has argued that Watt's discouraging Murdoch from working with high pressure steam (Watt rightly believed that boilers of the time would be unsafe) on his steam road locomotive experiments delayed its development.^[39]

Watt patented the application of the sun and planet gear to steam in 1781 and a steam locomotive in 1784, both of which have strong claims to have been invented by Murdoch.^[40] The patent was never contested by Murdoch, however, and Boulton and Watt's firm continued to use the sun and planet gear in their rotative engines, even long after the patent for the crank expired in 1794. Murdoch was made a partner of the firm in 1810, where he remained until his retirement 20 years later at the age of 76.

Legacy[link]

A preserved Watt beam engine at Loughborough University

James Watt's improvements to the steam engine "converted it from a prime mover of marginal efficiency into the mechanical workhorse of the Industrial Revolution".^[41] The availability of efficient, reliable motive power made whole new classes of industry economically viable, and altered the economies of continents.^[42] In doing so it brought about immense social change, attracting millions of rural families to the towns and cities.

Of Watt, the English novelist Aldous Huxley (1894–1963) wrote; "To us, the moment 8:17 A.M. means something – something very important, if it happens to be the starting time of our daily train. To our ancestors, such an odd eccentric instant was without significance – did not even exist. In inventing the locomotive, Watt and Stephenson were part inventors of time."^[43]

Honours[link]

Watt was much honoured in his own time. In 1784 he was made a fellow of the Royal Society of Edinburgh, and was elected as a member of the Batavian Society for Experimental Philosophy, of Rotterdam in 1787. In 1806 he was conferred the honorary Doctor of Laws by the University of Glasgow. The French Academy elected him a Corresponding Member and he was made a Foreign Associate in 1814.^[44]

The watt is named after James Watt for his contributions to the development of the steam engine, and was adopted by the Second Congress of the British Association for the Advancement of Science in 1889 and by the 11th General Conference on Weights and Measures in 1960 as the unit of power incorporated in the International System of Units (or "SI").

On 29 May 2009 the Bank of England announced that Boulton and Watt would appear on a new £50 note. The design is the first to feature a dual portrait on a Bank of England note, and presents the two industrialists side by side with images of Watt's steam engine and Boulton's Soho Manufactory. Quotes attributed to each of the men are inscribed on the note: "I sell here, sir, what all the world desires to have—POWER" (Boutlon) and "I can think of nothing else but this machine" (Watt). The inclusion of Watt is the second time that a Scot has featured on a Bank of England note (the first was Adam Smith on the 2007 issue £20 note).^[45] In September 2011 it was announced that the notes would enter circulation on 2 November.^[46]

Memorials[link]

The James Watt Memorial College in Greenock.

Watt was buried in the grounds of St. Mary's Church, Handsworth, in Birmingham. Later expansion of the church, over his grave, means that his tomb is now buried inside the church.^[47]

The garret room workshop that Watt used in his retirement was left, locked and untouched, until 1853, when it was first viewed by his biographer J. P. Muirhead. Thereafter, it was occasionally visited, but left untouched, as a kind of shrine. A proposal to have it transferred to the Patent Office came to nothing. When the house was due to be demolished in 1924, the room and all its contents were presented to the Science Museum, where it was recreated in its entirety.^[48] It remained on display for visitors for many years, but was walled-off when the gallery it was housed in closed. The workshop remained intact, and preserved, and in March 2011 was put on public display as part of a new permanent Science Museum exhibition, "James Watt and our world".^[49]

The approximate location of James Watt's birth in Greenock is commemorated by a statue. Several locations and street names in Greenock recall him, most notably the Watt Memorial Library, which was begun in 1816 with Watt's donation of scientific books, and developed as part of the Watt Institution by his son (which ultimately became the James Watt College). Taken over by the local authority in 1974, the library now also houses the local history collection and archives of Inverclyde, and is dominated by a large seated statue in the vestibule. Watt is additionally commemorated by statuary in George Square, Glasgow and Princes Street, Edinburgh, as well as several others in Birmingham, where he is also remembered by the Moonstones and a school is named in his honour.

The James Watt College has expanded from its original location to include campuses in Kilwinning (North Ayrshire), Finnart Street and The Waterfront in Greenock, and the Sports campus in Largs. Heriot-Watt University near Edinburgh was at one time the School of Arts of Edinburgh, founded in 1821 as the world’s first Mechanics Institute, but to commemorate George Heriot, the 16th century financier to King James, and James Watt, after Royal Charter the name was changed to Heriot-Watt University. Dozens of university and college buildings (chiefly of science and technology) are named after him. Matthew Boulton's home, Soho House, is now a museum, commemorating the work of both men. The University of Glasgow's Faculty of Engineering has its headquarters in the James Watt Building, which also houses the department of Mechanical Engineering and the department of Aerospace Engineering. The huge painting James Watt contemplating the steam engine by James Eckford Lauder is now owned by the National Gallery of Scotland.

Chantrey's statue of James Watt

There is a statue of James Watt in Piccadilly Gardens, Manchester and City Square, Leeds.

A colossal statue of Watt by Chantrey was placed in Westminster Abbey, and later was moved to St. Paul's Cathedral. On the cenotaph the inscription reads, in part, "JAMES WATT ... ENLARGED THE RESOURCES OF HIS COUNTRY, INCREASED THE POWER OF MAN, AND ROSE TO AN EMINENT PLACE AMONG THE MOST ILLUSTRIOUS FOLLOWERS OF SCIENCE AND THE REAL BENEFACTORS OF THE WORLD."

Patents[link]

Watt was the sole inventor listed on his six patents:^[50]

• Patent 913 A method of lessening the consumption of steam in steam engines-the separate condenser. The specification was accepted on 5 January 1769; enrolled on 29 April 1769, and extended to June 1800 by an act of Parliament in 1775.
• Patent 1,244 A new method of copying letters; The specification was accepted on 14 February 1780 and enrolled on 31 May 1780.
• Patent 1,306 New methods to produce a continued rotation motion – sun and planet. The specification was accepted on 25 October 1781 and enrolled on 23 February 1782.
• Patent 1,321 New improvements upon steam engines – expansive and double acting. The specification was accepted on 14 March 1782 and enrolled on 4 July 1782.
• Patent 1,432 New improvements upon steam engines – three bar motion and steam carriage. The specification was accepted on 28 April 1782 and enrolled on 25 August 1782.
• Patent 1,485 Newly improved methods of constructing furnaces. The specification was accepted on 14 June 1785 and enrolled on 9 July 1785.

Notes and references[link]

Bibliography[link]

• "Some Unpublished Letters of James Watt" in Journal of Institution of Mechanical Engineers (London, 1915).
• Carnegie, Andrew, James Watt University Press of the Pacific (2001) (Reprinted from the 1913 ed.), ISBN 0-89875-578-6.
• Dickinson, H. W. (1935). James Watt: Craftsman and Engineer. Cambridge University Press. 
• H. W. Dickinson and Hugh Pembroke Vowles James Watt and the Industrial Revolution (published in 1943, new edition 1948 and reprinted in 1949. Also published in Spanish and Portuguese (1944) by the British Council)
• Hills, Rev. Dr. Richard L., James Watt, Vol 1, His time in Scotland, 1736-1774 (2002); Vol 2, The years of toil, 1775-1785; Vol 3 Triumph through adversity 1785-1819. Landmark Publishing Ltd, ISBN 1-84306-045-0.
• Hulse David K. (1999). The early development of the steam engine. Leamington Spa, UK: TEE Publishing. pp. 127–152. ISBN 1-85761-107-1. 
• Hulse David K. (2001). The development of rotary motion by steam power. Leamington, UK: TEE Publishing Ltd.. ISBN 1-85761-119-5. 
• Marsden, Ben. Watt's Perfect Engine Columbia University Press (New York, 2002) ISBN 0-231-13172-0.
• Thomas H. Marshall (1925), James Watt, Chapter 3: Mathematical Instrument Maker, from Steam Engine Library of University of Rochester Department of History.
• Thomas H. Marshall (1925) James Watt, University of Rochester Department of History.
• Muirhead, James Patrick (1854). Origin and Progress of the Mechanical Inventions of James Watt. London: John Murray. http://books.google.com/?id=9lspAAAAYAAJ&printsec=frontcover&dq=Origin+and+Progress+of+the+Mechanical+Inventions+of+James+Watt.. 
• Muirhead, James Patrick (1858). The Life of James Watt. London: John Murray. http://books.google.com/?id=zUE6AAAAcAAJ&printsec=frontcover&dq=The+life+of+James+Watt+with+selections+from+his+correspondence. 
• Roll, Erich (1930). An Early Experiment in Industrial Organisation : being a History of the Firm of Boulton & Watt. 1775-1805. Longmans, Green and Co.
• Samuel Smiles, Lives of the Engineers, (London, 1861–62, new edition, five volumes, 1905).

Related topics

• Schofield, Robert E. (1963). The Lunar Society, A Social History of Provincial Science and Industry in Eighteenth Century England. Clarendon Press. 
• Uglow, Jenny (2002). The Lunar Men. London: Farrar, Straus and Giroux. 

External links[link]

Wikiquote has a collection of quotations related to: James Watt

Wikimedia Commons has media related to: James Watt

• James Watt by Andrew Carnegie (1905)
• James Watt by Thomas H. Marshall (1925)
• Archives of Soho at Birmingham Central Library.
• BBC History: James Watt
• Revolutionary Players website
• Cornwall Record Office Boulton and Watt letters
• Significant Scots - James Watt
• "Chapter 8: The Record of the Steam Engine". www.history.rochester.edu. http://www.history.rochester.edu/steam/carnegie/ch8.html. Retrieved 2009-07-06. 

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