PART TWO: POWER AND ENGINEERING
282
Figure 5.3: Corliss and drop valves.
(a) Schematic arrangement of Corliss valves. The valve is a machined cylinder
oscillating about an axis lying at right angles to the piston stroke. The upper
valves are the steam and the lower valves the exhaust valves. The valves are
loose on the valve spindle so they are free to find their seats under the action of
the steam pressure, and free to lift off their seats to allow trapped water to
escape.
Reproduced with permission from R.A.Buchanan, and G.Watkins The Industrial
Archaeology of the Stationary Steam Engine (Allen Lane, London, 1976).
(b) Trip gear that controls the cut-off of the Corliss valve. The valve is opened
by means of the oscillating link driven by the eccentric. When the connection at
the points A and B is broken the valve closes under the action of the powerful
spring. The moment of closure depends on the height h of the lever. As the
engine speed increases, h increases and the valve closes earlier. Closure of the
valve is assisted by atmospheric pressure acting on the exposed side of the dash-
pot piston and the vacuum formed on the other side when the valve is opened.
The exhaust valves are not provided with trip gear and the angular motion in
one direction is an exact repetition of the motion in the other direction.
STEAM AND INTERNAL COMBUSTION ENGINES
283
Reproduced with permission from D.A.Wrangham The Theory and Practice of Heat
Engines (Cambridge University Press, Cambridge, 1951).
(c) Schematic arrangement of equilibrium drop valves. The valves are mushroom
shaped and seat as shown. Motion is in the vertical direction. Note that identical
valves are mounted on the same stem so the pressures on the valve faces oppose
one another and a balanced arrangement is obtained. Consequently, the valve
operating force is only required to overcome friction and inertia. Because there
are no sliding parts (cf. Corliss valve) the valve is well adapted to use with
superheated steam.

Reproduced with permission from R.A.Buchanan and G.Watkins The Industrial
Archaeology of the Stationary Steam Engine (Allen Lane, London, 1976).

Admission and exhaust of the steam was controlled from the beginning of
the nineteenth century in most cases by the slide valve or in some cases, by the
poppet valve. Both types of valve were subject to wire drawing because they
did not close sufficiently quickly at the points of cut-off.
In 1842, F.E.Sickels took out a patent on a quick-closing valve gear using
poppet valves, and a trip gear to control the cut-off (see Figure 5.3), with
gravity assisted closure (called ‘drop-valves’ by Oliver Evans). To save wear
and tear on the valve seat and value face, Sickels used a water-filled dashpot
to decelerate the valve smoothly as it approached the end of its travel.
Sickels was not the only engineer who understood the advantages of rapid
valve operation, and in about 1847, G.H.Corliss invented a quick-closing valve
gear (patented in 1849) consisting of four flat slide valves, one inlet and one
outlet at each end of the cylinder, but he did not persist very long with this
valve gear. In order to simplify manufacturing and to reduce valve friction,
engines built by his company after about 1850 used the oscillating rotary valve
(see Figure 5.3) that is normally associated with his name. Corliss made an
evenmore fundamentally important contribution to steam engine technology
by replacing the inefficient method of throttle governing with the better
method of adjusting to load variations by using the governor to control the cut-
off, socalled cut-off governing.
Engines using Corliss valve gear (commonly called Corliss engines) were
built by Corliss, and his licencees from 1848, and by many others after the
Corliss patent expired in 1870. This type of engine was extensively used for
driving textile mill machinery where the close regulation of engine speed, that
was ensured by the governor control of cut-off, was essential.
The medium speed engine
Automatic trip gear mechanisms do no operate satisfactorily at rotational

speeds in excess of about 150rpm. Higher speeds became possible in 1858
when C.T. Porter combined his very sensitive governor with a positive action,
PART TWO: POWER AND ENGINEERING
284
variable cutoff valve gear that had been invented in 1852 by J.F.Allen. In 1861,
Porter and Allen formed a partnership to build engines using their two
inventions.
The outstanding feature of the Porter-Allen engine was its quiet,
vibrationfree operation at all speeds, which resulted from Porter’s careful study
of the dynamics of the reciprocating engine. Because of their high and closely
controlled speed, engines of this type were extensively used from about 1880
onward for driving electric generators, e.g. Edison’s Pearl Street Station.
The high speed engine
Steam engines operating with piston speeds in excess of 3m/s (600ft/min) could
be made sufficiently small, for a given power output, so that a significant
reduction in first cost could be realized compared to slower-running engines,
by the invention in the early 1870s of the shaft governor, which is usually
mounted on the flywheel shaft. This operates by balancing the force of the
governor spring against the centrifugal force. These had a tendency to hunt
(an inability of the governor to locate a steady operating speed) because the
rate at which they acted was independent of the rate of change of the load.
This fault was overcome by the invention in 1895 by F.M.Rites of the inertia
governor in which inertia forces augmented the centrifugal forces in the
governor. With this modification the high speed engine could be applied where
very close control of the engine speed was required, e.g. electric power
generations.
High speed engines were characterized by stroke: bore ratios less than unity,
and power outputs that did not usually exceed 370kW (500hp). Typically,
piston valves and cam-driven poppet valves were used for steam distribution.
Lubrication was particularly important and in 1890 the Belliss & Morcom Co.

in England introduced forced lubrication, which is now a standard feature of
any high speed machinery.
Many of the characteristic features of the high speed engine were carried
over into the early internal combustion engines, so that contemporary engines
of both types bear a considerable resemblance, both in superficial features and
in certain details.
Compound engines
The zenith of steam engine design was in the multiple expansion engines that
were developed in the second half of the nineteenth century. Such engines were
used in the largest numbers for water supply system pumping and as marine
engines, because efficiency was an important consideration in these applications.
STEAM AND INTERNAL COMBUSTION ENGINES
285
The inverted engine, in which the cylinders are arranged above the crankshaft
with the piston rod acting downwards, was the universal type in large multiple
expansion engines, because of the need to economize on floor space.
Stationary engines
Stationary compound engines were employed for operating the pumps of
public water supply systems and for turning electrical generators, as well as in
textile mills, as rolling mill drives, mine hoisting engines and blast furnace
blowing engines.
In 1866 a pressurized water supply system using a pump, rather than an
elevated reservoir or standpipe, started operating at Lockport, New York. This
development, which was to have a significant effect on the history of steam
pumping engines, was due to Birdsill Holly. The Lockport pumps were driven
by a water-wheel, but a second installation in Dunkirk, New York, used
steamdriven pumps.
The compound engine was first applied to water pumping in 1848 by the
Lambeth Water Works, London, but the employment of this type of engine
was not extensive until E.D.Leavitt installed such a machine at Lynn,

Massachusetts, in 1873. These engines were landmarks in both capacity and
efficiency, and their performance was not surpassed until H.F.Gaskill
introduced (1882) a pump driven by a Woolf compound steam engine at
Saratoga Springs, New York. This was a compact, high capacity, efficient steam
pump, which was very popular in the United States.
The first triple expansion pumping engine (see Figure 5.2 (d) above) was
built in 1886 for the City of Milwaukee. It was noteworthy in being designed
by E.T. Reynolds of the E.P.Allis Co. (later Allis-Chalmers). He joined this
company in 1877 from the Corliss Steam Engine Co., and was one of the chief
proponents of engines using the Corliss valve gear after the Corliss patent
expired in 1870.
Two 7500kW (10,000hp) double tandem compound engines were designed
in 1888 by S.Z.de Ferranti for use in the Deptford Power Station of the
London Electricity Supply Company. This was a pioneering AC distribution
system, but because substantial difficulties were encountered in placing it in
service, Ferranti’s connection with the company was terminated, and the
engines were never completed.
Somewhat later, in 1898, the Manhattan Railway Co., which operated the
overhead railway system in New York, purchased from the Allis-Chalmers Co.
compound engines with horizontal high pressure and vertical low pressure
cylinders. These unique engines, which were undoubtedly among the largest
stationary engines ever built, and probably the most powerful (6000kW;
8000hp), are usually known as the Manhattan engines.
PART TWO: POWER AND ENGINEERING
286
Marine engines
It was the application of the compound engine that allowed the steamship to
take over from the sailing vessel on the longest voyages. The consequent
reduction in coal consumption made more space available on the ship for
passengers and cargo, and fewer stops were needed to replenish the bunkers.

Compound engines had been tried in small vessels between 1830 and 1840,
but they were not fitted in ocean-going ships until 1854, when the Brandon was
launched by Randolph, Elder & Co., of Govan on the River Clyde in Scotland.
This had a Woolf compound engine with inclined cylinders and an overhead
crankshaft, designed by John Elder. Saturated steam was supplied at 2.8bar
(40psig), and in service the coal consumption was 2.13kg/kWhr (3.5lb/ihphr)
which was about a 30 per cent improvement over the performance of vessels
fitted with simple engines.
The compound engine was quickly adopted by British shipping companies
operating to ports in the East and in Africa. However, it was not until the
1870s that vessels operating on Atlantic routes were fitted with engines of this
type. By about 1880 the compound engine was used almost universally in
marine service, but between 1875 and 1900 triple expansion, and then
quadruple expansion engines, were adopted for the largest vessels.
The triple expansion engine was originally proposed in 1827 by Jacob
Perkins, but no engine of this type was built until 1861 by D.Adamson; this
was a stationary engine. The first application to a sea-going ship was by John
Elder & Co., who in 1874 fitted an engine using steam at 10.3bar (150psig)
with cylinders 580mm (23 inch)×1040mm (41 inch)×1550mm (61 inch) bore
by 1070mm (42 inch) stroke in the Propontis.
However, it was the Aberdeen, launched in 1880 by Robert Napier & Sons,
that had the greatest influence on the history of the marine engine. The engine
had cylinders 760mm (30 inch)×1140mm (45 inch)×1780mm (70 inch) bore
by 1370mm (58 inch) stroke. It used steam at 8.6bar (125psig) and had an
output of 1340kW (1800ihp). On its first voyage the coal consumption was
1.0kg/kWhr (1.7lbs/ihphr). This engine was the prototype for thousands of
marine engines that were built until the middle of the twentieth century:
Liberty ships were fitted with triple expansion engines.
The first quadruple expansion marine engine was fitted in the County of
York built at Barrow, Lancashire, in 1884, but this type of engine was not

tried again until 1894 when the Inchmona was launched, this was a 707kW
(948ihp) engine supplied with steam at 17.6bar (255psig) 33°C (60°F)
superheat.
The reciprocating steam engine undoubtedly reached its highest level in some
of the quadruple expansion engines built for the very large ocean-going liners at
the close of the nineteenth century. One of the most outstanding was the
29,830kW (40,000hp) engine produced for the twin-screw Kaiser Wilhelm II.
STEAM AND INTERNAL COMBUSTION ENGINES
287
Uniflow engine
The Uniflow engine, which represents the final stage of the development of the
steam engine, was motivated by the problem of cylinder condensation and
reevaporation, which was a serious cause of energy loss in the engine. Steam
enters the engine cylinder and is immediately exposed to cylinder walls that
have been cooled by the previous charge of steam, which had itself been
cooled in consequence of its expansion during the working stroke of the piston.
If the cylinder wall temperature is low enough, the incoming steam will
condense on the cylinder walls, and energy is given up to the walls. As the
expansion proceeds in the cylinder the steam temperature can fall below the
cylinder wall temperature, resulting in re-evaporation of the condensed steam.
However, because this occurs near the end of the stroke, very little of the
energy thus returned to the steam is available to do work and it is carried away
as the steam leaves the cylinder.
The question of cylinder condensation and re-evaporation became the
central concern of steam engine engineering from 1855 to 1885. Several
developments alleviated this problem, either deliberately or incidentally:
compounding; steam jacketing of the cylinders; superheating; and increasing
inlet steam pressure. While these techniques were used on large marine and
stationary engines, they were prohibitively expensive for the lower power
single-cylinder engines that were widely used in industrial applications: an

economical solution for engines of this type required a radically new design.
The requisite development was the introduction of one-way steam flow (hence
‘Uniflow’ or ‘Unaflow’) in the cylinder, so that steam was admitted at each end
of the cylinder and exhausted in the centre through circumferential ports in the
cylinder wall uncovered by the piston (Figure 5.4).
The Uniflow principle appears to have been proposed quite early in steam
engine history (Montgolfier, 1825; Perkins, 1827), but serious consideration of
the idea did not occur until T.J.Todd took out a British patent in 1885 on an
engine of this type (he called it the ‘Terminal-exhaust’ cylinder). It is not clear
if such an engine was ever built, so the practical realization of the Uniflow
engine is usually credited to J.Stumpf.
Uniflow engines were built in Europe, Britain and the United States. One of
the most successful builders was the Skinner Engine Company of Erie,
Pennsylvania. This company built Uniflow engines until the mid-1950s, and
during the Second World War supplied them for naval craft (where they were
popular because they generated less vibration than other types of reciprocating
engines).
The progress in the steam inlet pressure and the heat rate between the time
of Newcomen (1712) and the end of the nineteenth century is indicated in
Figure 5.5. The data for the earliest years do not have the precision and
accuracy of the later period, nevertheless they are indicative of the general
PART TWO: POWER AND ENGINEERING
288
trend. In the final decade of the nineteenth century, the introduction of
regenerative feed-water heating, in which steam used in the cylinder jackets
was returned to the boiler, had a marked effect in lowering the best values for
the heat rate. In fact, the best of the final generation of reciprocating steam
engines with cylinder steam-jacketing had heat rates that were comparable with
those of contemporary non-regenerative steam turbines (typically 23.0×103
btu/kWhr; see Figure 5.10).

STEAM TURBINES
The steam turbine is a device that directly converts the internal energy of
steam into rotary motion (see Appendix). It is also characterized by uniformity
Figure 5.4: Schematic section of a Uniflow engine. The diagram shows the
Uniflow steam path and the small difference in temperature between the steam
and the cylinder wall throughout the piston stroke. Since the exhaust ports must
not be uncovered until the piston reaches the end of the expansion stroke the
piston length must equal its stroke. Hollow construction is used to reduce the
piston weight. Because the return stroke of the piston is a compression stroke
and because the compression ratio (expansion ratio for the expanding steam) is
high, typically 46, there is a danger that the pressure of the residual steam in the
cylinder could become high enough to dislodge the cylinder head cover. This is
avoided by providing additional clearance space, in the form of a cavity in the
cylinder head connected to the cylinder by a spring-loaded valve, with manual
override for starting the engine, or by using various types of automatic and
manual valves that divert the residual steam into the exhaust.
Reproduced with permission from D.A.Wrangham, The Theory and Practice of Heat
Engines (Cambridge University Press, Cambridge, 1951).
STEAM AND INTERNAL COMBUSTION ENGINES
289
of turning moment and by the possibility of balancing it perfectly, which is
important where high powers are involved, when a reciprocating engine would
have correspondingly massive dimensions that could produce vibrations of an
unacceptable magnitude.
Because the steam flow through the turbine is continuous rather than cyclic,
it is able to expand steam from a high pressure to a very low pressure, thereby
maximizing the efficiency. This, because of the low density of the low pressure
steam, would require the cylinder of a reciprocating engine to have
impracticably large dimensions.
The continuous flow characteristics of the steam turbine allow it to avoid

the complex valve gear necessary in the reciprocating engine, which should
Figure 5.5: The historical trend of reciprocating steam engine inlet pressure
(boiler pressure) and power plant heat rate between 1800 and 1900. The data
shown are based on marine practice, but are also representative of stationary
engines. The upward trend beginning between 1850 and 1860 marks the
introduction of the compound engine. To convert heat rate to efficiency multiply
by 2.93×10-4 and invert.
Adapted with permission from R.H.Thurston, A History of the Growth of the Steam
Engine, Centennial edition (Cornell University Press, Ithaca, N.Y., 1939).
PART TWO: POWER AND ENGINEERING
290
have made it attractive to the ancients, and indeed there is some historical
evidence that a turbine was built in the first century AD by Hero in
Alexandria. Later, in the seventeenth century, an Italian, de Branca, proposed
another type of steam turbine. Unfortunately, these primitive machines
suffered from the fatal defect that, for their times, their speed was too high to
be either needed or useable. Consequently, the practical steam turbine had to
await the development of the ability to design and construct high speed
gears, or high speed electrical generators, or the formulation of such
principles of fluid mechanics as would allow the energy of the steam to be
utilized without high rotational speeds. None of this occurred until the end of
the nineteenth century.
1884–1900: early history
The simplest form of turbine (Figure 5.6 (a)), which was first demonstrated by
the Swedish engineer Gustav de Laval in c.1883, is constructed by arranging
the blades on a single revolving wheel in such a way that they turn the steam
through an angle, thereby imparting a portion of the kinetic energy of the
steam jets to the rotating blades with no change in steam pressure as it passes
through them. This last is an important distinguishing characteristic of this
type of turbine, which is sometimes known as an impulse turbine. In about

1888, de Laval made the crucial discovery that in order to extract the
maximum amount of energy from the steam, the nozzle had to be of a
converging-diverging form (see Appendix). This results in a very high steam
velocity, leading to: (a) high rotational speeds (10,000–30,000rpm), which
usually requires a speed reducing gear for its practical utilization; (b) wasted
kinetic energy in the leaving steam; (c) large friction losses between the steam,
the blades, and the turbine rotor. The losses, items (b) and (c), make the
efficiency of the de Laval turbine inferior to that of a reciprocating engine
operating with identical inlet and exhaust conditions.
The principles of the impulse turbine, and its problems, were well known to
nineteenth-century engineers, including James Watt. Consequently, until the
close of the century it was never considered a serious competitor to the
reciprocating engine. The steam turbine was first placed on a practical basis by
C.A. Parsons. He took out a patent in 1884 on a turbine which avoided the
limitations of the impulse turbine by using the steam pressure drop inlet to
exhaust in small steps rather than one large step (see Figure 5.6 (b)), resulting
in a much lower steam speed. However, there is an important difference
between the Parsons and impulse turbines in the way in which the pressure
drop is arranged in a stage (a pair of moving blades and stationary nozzles): in
the former the pressure drop occurs in both the rotating and stationary
elements, while in the impulse turbine the pressure drop only occurs in the
STEAM AND INTERNAL COMBUSTION ENGINES
291
stationary element. The Parsons turbine is known as a reaction turbine, and
since Parsons arranged for equal pressure drops to occur in both the stationary
and rotating elements of each stage, it is called a 50 per cent reaction turbine.
Parsons commenced experimental work on his turbine shortly after
becoming a partner in 1883 in the firm of Clarke, Chapman & Co. In 1885
he constructed his first working turbine Figure 5.7 which drove an electrical
generator at 18,000rpm having an output that appears to have been between

about 4kW (5.4hp) and 7.5kW (10hp). The surprisingly high speed,
considering the Parsons turbine was intended to avoid this feature of the de
Laval turbine, is a consequence of the small dimensions of the first Parsons
turbine. Thus, an increase in the mean blade radius from 4.4cm (1.75 inches)
(estimated for Parsons’s first turbine) to 26.7cm (10.6 inches) would reduce
the rotational speed to 3000rpm. The essential point is the lower steam speed
in the Parsons turbine compared to the de Laval turbine. Thus, for
comparable steam conditions, the steam speed in the de Laval turbine is
about 760m/s, (2500ft/sec), whereas in the Parsons turbine it is about 116m/s
(380ft/sec).
From 1885 until 1889 development of the Parsons turbine was very rapid
with machines of maximum output 75kW being ultimately produced.
However, Parsons’s partners did not have his faith in the steam turbine, so in
1889 the partnership was dissolved. Parsons founded C.A.Parsons & Co. and
proceeded to develop a radial reaction turbine that circumvented the patents
controlled by his former partners (a truly remarkable achievement). In 1894,
Parsons came to an agreement with Clarke, Chapman that allowed him to
use his 1884 patents for the axial flow steam turbine, and, as a result,
construction of the radial flow steam turbine stopped.
Although the Parsons turbine was in many ways significantly superior to
the de Laval turbine, it did have some disadvantages. In particular, it was
difficult to build with outputs greater than 2000kW (2682hp). This was a
consequence of the great length of the machine, which was necessitated by the
numerous rows of moving and stationary blades that were required to keep the
steam velocity low. As a result the rotor was particularly sensitive to slight
mechanical and thermal imbalances that could lead to distortion and, hence,
damage to the moving blades if they touched the turbine casing. The
techniques that were eventually devised to overcome this problem are
discussed below.
In addition to the limitations in size that were encountered in the early

Parsons turbine, there is a substantial loss in power output due to leakage
through the clearance space between the rotating blades and the turbine casing,
which is particularly serious in the high pressure sections of the turbine where
the blade heights are small. In order to avoid this leakage problem and yet
retain the advantages of the Parsons multi-stage concept, Auguste Rateau, a
French engineer, designed sometime between 1896 and 1898 a multi-stage