High pressure steam locomotive
Encyclopedia
A high-pressure steam locomotive is a steam locomotive
with a boiler
that operates at pressures well above what would be considered normal. In the later years of steam, boiler pressures were typically 200 to 250 psi (1.4 to 1.7 MPa). High-pressure locomotives can be considered to start at 350 psi (2.41 MPa), when special construction techniques become necessary, but some had boilers that operated at over 1500 psi (10.34 MPa).
depends fundamentally upon getting the temperature at which heat is accepted (ie raising steam in the boiler
) as far as possible from the temperature at which it is rejected (ie the steam when it leaves the cylinder). This was quantified by Nicolas Léonard Sadi Carnot
.
There are two options: raise the acceptance temperature or lower the rejection temperature. For a steam engine
, the former means raising steam at higher pressure and temperature, which is in engineering terms fairly straightforward. The latter means bigger cylinders to allow the exhaust steam to expand further - and going this direction is limited by the loading gauge
- and possibly condensing
the exhaust to further lower the rejection temperature. This tends to be self-defeating because of frictional losses in the greatly increased volumes of exhaust steam to be handled.
Thus it has often been considered that high-pressure is the way to go to improve locomotive fuel efficiency. However, experiments in this direction were always defeated by much increased purchase and maintenance costs.
High-pressure locomotives were much more complicated than conventional designs. It was not simply a matter of building a normal fire-tube boiler
with suitably increased strength and stoking harder. Structural strength requirements in the boiler shell make this impractical; it becomes impossibly thick and heavy. For high steam pressures the water-tube boiler
is universally used. The steam drums and their interconnecting tubes are of relatively small diameter with thick walls and therefore much stronger.
The next difficulty is that of scale deposition and corrosion
in the boiler tubes. Scale deposited inside the tubes is invisible, usually inaccessible, and a deadly danger, as it leads to local overheating and failure of the tube. This was a major drawback with the early water-tube boilers, such as the Du Temple design, tested on the French Nord network in 1907 and 1910. Water tubes in Royal Navy boilers were checked for blockage by carefully dropping numbered balls down the curved tubes.
A sudden steam leak into the firebox is perilous enough with a conventional boiler- the fire is likely to be blasted out of the firebox door, with unhappy results for anyone in the way. With a high-pressure boiler the results are even more dangerous because of the greater release of energy. This was demonstrated by the Fury
tragedy, though the reason for the tube failure in that case was concluded to be overheating due to lack of steam flow rather than scaling.
. Perkins applied his "hermetic tube" system to steam locomotive boilers and a number of locomotives using this principle were made in 1836 for the London and South Western Railway
.
, as is done in power station
s. In fact you need to go further: dissolved gases such as oxygen
and carbon dioxide
also cause corrosion at high temperatures and pressures, and must be kept out. Most locomotives did not lug a condenser around with them, so there was no source of pure feed water. One solution was the Schmidt system; this used a sealed ultra-high-pressure circuit that simply transferred heat to a high-pressure circuit, by means of heating coils inside a high-pressure boiler. If this latter is fed with ordinary water, scale may form on the outside of the heating coils, but it cannot cause overheating, as the ultra-HP tubes are quite capable of withstanding their internal steam temperature, though not the firebox flame temperature.
The sealed ultra-high-pressure circuit ran at between 1200 and 1600 psi (8.3 and 11 MPa), depending on the rate of firing. The HP boiler worked at approx 850 psi (5.86 MPa), and the low-pressure boiler at 200 to 250 psi (1.4 to 1.7 MPa). The UHP and HP boilers were of a water tube design, while the LP boiler was a fire tube boiler typical for steam locomotives. The LP cylinders were driven with a mixture of the HP cylinder exhaust and the LP boiler output. Both HP and LP boilers had superheater
s.
The French PL241P
, the German H17-206
and the British LMS 6399 Fury
all used the Schmidt system, and were of basically similar design. The New York Central HS-1a and the Canadian 8000 also used the Schmidt system but were a size larger altogether- the 8000 weighed more than twice the Fury.
Saturated steam from an HP steam generator was pumped through HP superheater tubes which lined the firebox. There it was superheated to about 900 °F (482 °C) and the pressure raised to 1700 psi (11.72 MPa). Only a quarter of this was fed to the HP cylinders; the rest was returned to the steam generator where its heat evaporated more water to continue the cycle.
The HP cylinder exhaust passed through an LP feed heater, and then the tubes of an LP boiler; this was roughly equivalent to the LP boiler in the Schmidt system, but was heated by HP exhaust steam not combustion gases. Steam was raised in the LP boiler at 225 psi (1.55 MPa), fed to the LP superheater, and then the LP cylinder. The LP exhaust fed the blastpipe in the smokebox. The HP exhaust condensed in the LP boiler heating tubes was pumped back to the HP steam generator.
It was a complex system.
The only locomotive built using this system was the German DRG H 02 1001 of 1930. It was not a success, being hopelessly unreliable.
prototype worked at a modest 350 psi (2.41 MPa) and did not use either of the complex systems described above. It had a relatively conventional watertube firebox and a firetube boiler. Nevertheless, high maintenance costs and poor reliability more than cancelled the fuel economies promised by high-pressure and compounding, and the design was not repeated.
Other relatively conventional high-pressure locomotives were built in the USA, including the remarkable triple-expansion L F Loree locomotive of 1933. None was successful.
Steam locomotive
A steam locomotive is a railway locomotive that produces its power through a steam engine. These locomotives are fueled by burning some combustible material, usually coal, wood or oil, to produce steam in a boiler, which drives the steam engine...
with a boiler
Boiler
A boiler is a closed vessel in which water or other fluid is heated. The heated or vaporized fluid exits the boiler for use in various processes or heating applications.-Materials:...
that operates at pressures well above what would be considered normal. In the later years of steam, boiler pressures were typically 200 to 250 psi (1.4 to 1.7 MPa). High-pressure locomotives can be considered to start at 350 psi (2.41 MPa), when special construction techniques become necessary, but some had boilers that operated at over 1500 psi (10.34 MPa).
The reason for high pressure
Maximising the efficiency of a heat engineHeat engine
In thermodynamics, a heat engine is a system that performs the conversion of heat or thermal energy to mechanical work. It does this by bringing a working substance from a high temperature state to a lower temperature state. A heat "source" generates thermal energy that brings the working substance...
depends fundamentally upon getting the temperature at which heat is accepted (ie raising steam in the boiler
Boiler
A boiler is a closed vessel in which water or other fluid is heated. The heated or vaporized fluid exits the boiler for use in various processes or heating applications.-Materials:...
) as far as possible from the temperature at which it is rejected (ie the steam when it leaves the cylinder). This was quantified by Nicolas Léonard Sadi Carnot
Nicolas Léonard Sadi Carnot
Nicolas Léonard Sadi Carnot was a French military engineer who, in his 1824 Reflections on the Motive Power of Fire, gave the first successful theoretical account of heat engines, now known as the Carnot cycle, thereby laying the foundations of the second law of thermodynamics...
.
There are two options: raise the acceptance temperature or lower the rejection temperature. For a steam engine
Steam engine
A steam engine is a heat engine that performs mechanical work using steam as its working fluid.Steam engines are external combustion engines, 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...
, the former means raising steam at higher pressure and temperature, which is in engineering terms fairly straightforward. The latter means bigger cylinders to allow the exhaust steam to expand further - and going this direction is limited by the loading gauge
Loading gauge
A loading gauge defines the maximum height and width for railway vehicles and their loads to ensure safe passage through bridges, tunnels and other structures...
- and possibly condensing
Condenser (steam turbine)
A surface condenser is a commonly used term for a water-cooled shell and tube heat exchanger installed on the exhaust steam from a steam turbine in thermal power stations. These condensers are heat exchangers which convert steam from its gaseous to its liquid state at a pressure below atmospheric...
the exhaust to further lower the rejection temperature. This tends to be self-defeating because of frictional losses in the greatly increased volumes of exhaust steam to be handled.
Thus it has often been considered that high-pressure is the way to go to improve locomotive fuel efficiency. However, experiments in this direction were always defeated by much increased purchase and maintenance costs.
High-pressure locomotives were much more complicated than conventional designs. It was not simply a matter of building a normal fire-tube boiler
Fire-tube boiler
A fire-tube boiler is a type of boiler in which hot gases from a fire pass through one or more tubes running through a sealed container of water...
with suitably increased strength and stoking harder. Structural strength requirements in the boiler shell make this impractical; it becomes impossibly thick and heavy. For high steam pressures the water-tube boiler
Water-tube boiler
A water tube boiler is a type of boiler in which water circulates in tubes heated externally by the fire. Fuel is burned inside the furnace, creating hot gas which heats water in the steam-generating tubes...
is universally used. The steam drums and their interconnecting tubes are of relatively small diameter with thick walls and therefore much stronger.
The next difficulty is that of scale deposition and corrosion
Corrosion
Corrosion is the disintegration of an engineered material into its constituent atoms due to chemical reactions with its surroundings. In the most common use of the word, this means electrochemical oxidation of metals in reaction with an oxidant such as oxygen...
in the boiler tubes. Scale deposited inside the tubes is invisible, usually inaccessible, and a deadly danger, as it leads to local overheating and failure of the tube. This was a major drawback with the early water-tube boilers, such as the Du Temple design, tested on the French Nord network in 1907 and 1910. Water tubes in Royal Navy boilers were checked for blockage by carefully dropping numbered balls down the curved tubes.
A sudden steam leak into the firebox is perilous enough with a conventional boiler- the fire is likely to be blasted out of the firebox door, with unhappy results for anyone in the way. With a high-pressure boiler the results are even more dangerous because of the greater release of energy. This was demonstrated by the Fury
LMS 6399 Fury
The London Midland and Scottish Railway 6399 Fury was an unsuccessful British experimental express passenger locomotive. The intention was to save fuel by using high-pressure steam, which is thermodynamically more efficient than low-pressure steam....
tragedy, though the reason for the tube failure in that case was concluded to be overheating due to lack of steam flow rather than scaling.
Jacob Perkins
An early experimenter with high-pressure steam was Jacob PerkinsJacob Perkins
Jacob Perkins was an Anglo-American inventor, mechanical engineer and physicist. Born in Newburyport, Massachusetts, Perkins was apprenticed to a goldsmith...
. Perkins applied his "hermetic tube" system to steam locomotive boilers and a number of locomotives using this principle were made in 1836 for the London and South Western Railway
London and South Western Railway
The London and South Western Railway was a railway company in England from 1838 to 1922. Its network extended from London to Plymouth via Salisbury and Exeter, with branches to Ilfracombe and Padstow and via Southampton to Bournemouth and Weymouth. It also had many routes connecting towns in...
.
The Schmidt system
One way to avoid corrosion and scale problems at high pressure is to use distilled waterDistilled water
Distilled water is water that has many of its impurities removed through distillation. Distillation involves boiling the water and then condensing the steam into a clean container.-History:...
, as is done in power station
Power station
A power station is an industrial facility for the generation of electric energy....
s. In fact you need to go further: dissolved gases such as oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
and carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
also cause corrosion at high temperatures and pressures, and must be kept out. Most locomotives did not lug a condenser around with them, so there was no source of pure feed water. One solution was the Schmidt system; this used a sealed ultra-high-pressure circuit that simply transferred heat to a high-pressure circuit, by means of heating coils inside a high-pressure boiler. If this latter is fed with ordinary water, scale may form on the outside of the heating coils, but it cannot cause overheating, as the ultra-HP tubes are quite capable of withstanding their internal steam temperature, though not the firebox flame temperature.
The sealed ultra-high-pressure circuit ran at between 1200 and 1600 psi (8.3 and 11 MPa), depending on the rate of firing. The HP boiler worked at approx 850 psi (5.86 MPa), and the low-pressure boiler at 200 to 250 psi (1.4 to 1.7 MPa). The UHP and HP boilers were of a water tube design, while the LP boiler was a fire tube boiler typical for steam locomotives. The LP cylinders were driven with a mixture of the HP cylinder exhaust and the LP boiler output. Both HP and LP boilers had superheater
Superheater
A superheater is a device used to convert saturated steam or wet steam into dry steam used for power generation or processes. There are three types of superheaters namely: radiant, convection, and separately fired...
s.
The French PL241P
French PL241P
The PLM 241 B 1 was a high-pressure steam locomotive built in 1929 for the PLM using the Schmidt high-pressure system...
, the German H17-206
German H17-206
H17-206 was a high pressure steam locomotive built in Germany in 1925 by Henschel, on the Schmidt system. Rebuilt from a Prussian S 10.2.*Wheel arrangement: 4-6-0*Boiler Pressure: 60 kp/cm² *Coal-fired.*Compound....
and the British LMS 6399 Fury
LMS 6399 Fury
The London Midland and Scottish Railway 6399 Fury was an unsuccessful British experimental express passenger locomotive. The intention was to save fuel by using high-pressure steam, which is thermodynamically more efficient than low-pressure steam....
all used the Schmidt system, and were of basically similar design. The New York Central HS-1a and the Canadian 8000 also used the Schmidt system but were a size larger altogether- the 8000 weighed more than twice the Fury.
The Schwarzkopff-Löffler system
Another way to avoid scaling in the HP boiler is to use steam alone to transfer the heat from the fire; steam cannot of course deposit scale.Saturated steam from an HP steam generator was pumped through HP superheater tubes which lined the firebox. There it was superheated to about 900 °F (482 °C) and the pressure raised to 1700 psi (11.72 MPa). Only a quarter of this was fed to the HP cylinders; the rest was returned to the steam generator where its heat evaporated more water to continue the cycle.
The HP cylinder exhaust passed through an LP feed heater, and then the tubes of an LP boiler; this was roughly equivalent to the LP boiler in the Schmidt system, but was heated by HP exhaust steam not combustion gases. Steam was raised in the LP boiler at 225 psi (1.55 MPa), fed to the LP superheater, and then the LP cylinder. The LP exhaust fed the blastpipe in the smokebox. The HP exhaust condensed in the LP boiler heating tubes was pumped back to the HP steam generator.
It was a complex system.
The only locomotive built using this system was the German DRG H 02 1001 of 1930. It was not a success, being hopelessly unreliable.
The straightforward approach
The Baldwin 60000Baldwin 60000
Baldwin 60000 is an experimental steam locomotive built by the Baldwin Locomotive Works in Eddystone, Pennsylvania in 1926, during the height of the railroading industry. It received its number for being the 60,000th locomotive built by Baldwin....
prototype worked at a modest 350 psi (2.41 MPa) and did not use either of the complex systems described above. It had a relatively conventional watertube firebox and a firetube boiler. Nevertheless, high maintenance costs and poor reliability more than cancelled the fuel economies promised by high-pressure and compounding, and the design was not repeated.
Other relatively conventional high-pressure locomotives were built in the USA, including the remarkable triple-expansion L F Loree locomotive of 1933. None was successful.
External links
- Loco Locomotives A large amount of information on high-pressure steam locomotives, as well as many other rail oddities.