Last modified on 26 May 2013, at 04:31

Steam Locomotive Operation

This book is an operators manual for the operation of functional steam locomotives. The terms and procedures described here will enable a person to safely operate a 19th or 20th century steam locomotive well into the future.

To hostle, fire, or engineer a locomotive effectively, efficiently, and safely, a person should have a good understanding of the construction and the physics that go into a steam engine to produce locomotion as well as an understanding of normal operating techniques.

Locomotive Construction and PartsEdit

The BoilerEdit

A common later (1940s) boiler design was the radial stay extended wagon top type of locomotive boiler, which consists of an oblong box with a circular top made of steel plating, connected to a cylindrical part which is commonly known as the barrel of the boiler. That part of the boiler enclosing the firebox is known as the outer casing, or shell. The firebox corresponds in shape to the back end and sides of the outer casing or shell, a space being provided between the firebox sheets and those of the outer casing which provides for the firebox being surrounded by water. The front, or cylindrical part of the boiler encloses the flues which are secured at the front to the front flue sheet and at the back to the inner or firebox flue sheet.

This arrangement provides that all parts of the firebox, as well as the flues are completely surrounded by water, and it also provides that when fuel is burned in the firebox, the heat will be transmitted by the flues and firebox plates to the water; the unused gasses and smoke having free passage from the firebox through the flues to the smoke box and smoke stack.

The smoke box is formed by extending the cylindrical part of the boiler beyond the front flue sheet. The boiler shell is provided with a steam dome on top of the shell which forms a chamber where steam may collect and free itself from the water in the boiler before passing through the throttle valve to the cylinders.

The flues in a locomotive boiler are known as fire tubes, because the heat passes through them, while the arch tubes, of which there are usually four in each firebox are called "water tubes" because the fire is on the outside, and the water passes through them.

The firebox sheets and flues constitute what is known as the heating surface. In addition to this heating surface there is additional, or superheater heating surface in many boilers, which superheats the steam after it leaves the boiler and while it is passing from the boiler to the cylinders. Comparing the flue heating area with that of the area of the firebox plates shows that the plate heating surface equals only 5% of the flue heating surface, but the firebox heating surface generates about 40% of the steam. This fact should be remembered.

In the locomotive boiler a large number of small flues are provided instead of a few large flues, in order that the heat and gasses passing from the firebox to the smoke box will be split up and come into contact with a larger flue surface. If large flues were used, great quantities of heat would pass through the center of the flues without coming into contact with the surface of the flue, such heat would pass away and be lost. A large number of small tubes also provides for the heat being more evenly distributed through the boiler shell water space. The small flue can be made of thinner material, which permits the heat to be more easily transmitted to the water which surrounds the flues. In the extended wagon top type of locomotive boiler, the back part, or outer shell, is considerably larger in diameter than the front section, or cylindrical part; while the straight type of boiler has the outer shell and cylindrical part of practically the same diameter. The extended wagon top type therefore allows more steam and water space, and gives superior performance in foaming water conditions.

Locomotive boilers are made entirely of steel, except stay-bolts and stays, which are of iron. The crown sheet is supported by what are called radial stays, reaching from the crown sheet to the exterior wrapper sheet.

There are three common designs of fireboxes in general use. The narrow, deep firebox, which is between the frames and extends below the top frame rails. The semi-wide shallow firebox which rests on top of the frames and extends to the outside edges of the frame rails, and the wide firebox type having a firebox wider than the frames and extending outside the frame rails on both sides, and resting on top of the frame rails, or expansion brackets which are secured to the top of the frames.

Combustion ChamberEdit

The combustion chamber for large locomotives was originally introduced for the purpose that its name implies, of providing increased firebox area for combustion purposes. As locomotives grew larger and the wheel base longer, it then became a question of limiting the length of flues. It was found that when flues were more than 21 or 22 feet long, there was considerable more trouble in respect to leakage and in order to keep the flues within those limits of length it was necessary to lengthen out the firebox, which was done by extending the flue area into the boiler.

There is also an advantage of the combustion chamber, in addition to allowing shorter flues, the heating surface of the firebox sheets composing the combustion chamber is vastly more efficint than the increased length of flues would be if the combustion chamber was not used.

The combustion chamber also serves to protect the ends of the tubes from cold air which comes up through the grates at the front end of the firebox, in addition to providing a long flameway for the burning gases, which is particularly desirable with oil, or coal, having a large percentage of volatile matter.

Effect of Heating, Cooling, and Low WaterEdit

When the crown sheet or firebox sheets are not covered with water, they become overheated very quickly with a hot fire in the firebox. If for any reason water is not maintained over the crown sheet, and the sheet becomes overheated, the fire must be put out or deadened at once, and under no circumstances should cold water be forced into the boiler. The boiler should be cooled down before any attempt is made to refill it, because forcing cold water into the boiler when it is very hot produces sudden changes in temperature of the various parts of the sheets and sets up destructive strains.

The prevention of destructive strains and stresses, or reducing their amplitude should interest all who have to do with the upkeep of the locomotive. In order to bring out clearly and simply the cause of destructive stresses, it should fully be understood that the contraction or expansion of a body of metal when changes of temperature occur is irresistible. A firebox sheet expanding or contracting as a result of a change in temperature cannot be restrained. It is certain to find relief in some direction, either by self destruction or destroying the obstacle opposing its movement.

The life of a locomotive boiler or firebox is dependent largely upon the care which it receives while in service. It is not possible in the operation of a locomotive to avoid all strains and stresses, but it is possible, practical, and beneficial to reduce the frequency of the stresses and also their amplitude. In other words, if by any means the severity of the strains is reduced even though their frequency be increased, the period between failures will be prolonged, the time between repairs and the life of fireboxes and boilers will be lengthened.

Figure 3, which is a diagram of the boiler shown in Figure 1, illustrates the action of metal when heating and cooling takes place. It will be noted that the boiler is divided into sections. After steam is generated in the boiler to 200lbs per square inch, it is found that the boiler has expanded nearly one inch, which demonstrates that the metal expands as heating takes place and that when the boiler cools the metal contracts. Expansion and contraction of the metals thus sets up strains and stresses at various parts in the boiler, and it is important that as these strains are developed that they be developed slowly, in order that the effect of heating or cooling will be distributed throughout the boiler so that the expansion or contraction will be as uniform as possible throughout all its parts.

Temperatures of Steam and WaterEdit

Operating a water injector or water pump while locomotive is standing causes more frequent and greater inequality of temperatures throughout the boiler and the development of more destructive stresses than any other cause. To illustrate: Temperature of the steam in a locomotive boiler at 190 psi is 383 degrees Fahrenheit (195 degrees Centigrade). This is also the temperature of the water at that steam pressure. When an injector is operated, the water passing through the injector on its way to the boiler is heated from 160 to 200 degrees F (71 to 93 degrees C). It is therefore from 183 to 223 degrees F (102-124 deg C) cooler than the water within the boiler. The water from the injector being cooler is heavier than the higher temperature water in the boiler, and on entering the boiler must take a downward course and continue downward until it reaches the lowest part. The weight of a cubic foot of water as it enters the boiler from the injectors is 60 1/8 pounds, while a cubic foot of water at 190 psi steam pressure, or 383 degrees Fahrenheit, is 54 1/4 pounds, or 9% lighter than the water at 200 degrees delivered into the boiler from the injector. This difference of weight makes it clear why the cooler and heavier water seeks the lower levels and displaces the hotter, lighter water.

Table Showing Temperatures of Steam at Different Pressures
Boiling point               212   F                     100.0 C
100 psi                     337.8 F                     169.9 C
160 psi                     370.6 F                     188.1 C
180 psi                     379.5 F                     193.1 C
200 psi                     387.8 F                     197.7 C
220 psi                     395.6 F                     202.0 C
250 psi                     406   F                     207.8 C
300 psi                     421.7 F                     216.5 C

-Quick reference to Water boiling point (Not Steam Temp) at different pressures- The boiling point of water raises 3 degrees F per each pound of square inch pressure added. For example: at sea level, water will boil at 212 degrees F (100 deg C). +1 PSI over sea level it will raise the boiling point 3 degrees F, to 215 degrees F (1.7 deg C, to 101.7 deg C). At +5 PSI over sea level the boiling point of water will be 227 degrees F (108.3 deg C). And so on. This is why directions for boiling noodles and baking goods at high altitudes require longer cook times, and/or more water added to mixture.

The steam circuitEdit

Steam locomotive work.gif

The CrewEdit

HostlerEdit

The hostler prepares an engine each day for service. This usually includes starting the fire, greasing and oiling all lubrication points on a steam locomotive. This was traditionally the starting point for a person coming onto the engine crew.

Additonally, Hostlers service locomotives with fuel and water, sand and lubricants and assure that all required tools and flagging equipment are provided on the locomotive. The firebox is cleaned or banked as necessary upon arrival at the locomotive.

FiremanEdit

The fireman maintains the steam pressure in a locomotive boiler. This is accomplished through careful regulation of the fire, and by regular addition of water to the boiler. Water is added through the use of an injector or feed water pump. In the absence of an Engineer, he will be responsible for the safety and security of the locomotive. Locomotive Firemen will not operate locomotives unless under the direct supervision of a qualified Engineer.

EngineerEdit

The engineer is responsible for ensuring that the engine is fit for operation before and during any movement of the locomotive. The engineer is responsible for its over the road upkeep, oiling and proper operation of the locomotive to be most fuel efficient and easy on the machinery. The engineer controls the operation of the locomotive but the conductor controls the movement of the train, and both are responsible for its safe operation. The steam whistle, headlight, throttle, air brakes, reverse lever, and fireman are usually under the direct control of the engineer.

FiringEdit

Firing involves caring for the boiler, and making sure there is always sufficient steam for the engineer to use. When proficient, a fireman should concentrate on efficient operation to conserve fuel, water and extend the life of the engine. This is especially important in the 21st century as working steam engines are rare and often in precarious financial situations.

General PracticesEdit

The boiler of a locomotive is made of a steel alloy and holds thousands of gallons of water. The boiler must be treated with care at all times, as it must withstand tremendous amounts of heat, pressure and vibration. The fireman should take care to minimize the thermal stresses placed on the boiler when safety permits.

Fire less LocomotivesEdit

Fire less locomotives generally used a tank (in place of a boiler and firebox) filled with super heated water that flashed into steam as the pressure from working existing steam dropped the pressure (refer to pressure table above). Fire less locomotives were tied to operating in an area where they could obtain water heated higher than the boiling point while a fire was undesirable for safety reasons. They were used mostly in industries or a group of industries, and due to this limitation were not common for moving trains on main lines. They were replaced by explosion proof diesel or electric locomotives. There are no references to currently operating fire less locomotives found by this author.

Wood Burning LocomotivesEdit

Wood burning locomotives fell into disfavor in the United States once expansion into the western plain states began, chiefly because of the generally lower amount of thermal energy wood locomotives offered from the fuel, and the scarcity of forests in the plain states.

Oil Burning LocomotivesEdit

Oil burning locomotives in the steam era mainly used "Bunker C" fuel oil. (Bunker C is also known as Type 6 or Number 6.)[1] While some preserved steam locomotives of today (circa 2005) still use Bunker C, most have switched to various alternative fuels as Bunker C can be difficult to locate, transport, and store. Alternatives include Number 4 fuel oil, kerosene or diesel oil (and sometimes a mixture of diesel/kerosene), others employ used motor oil.

Regardless of the kind of oil used, most locomotives store the fuel in a tank on the tender. The oil tank is equipped with steam heat coils to heat the fuel before combustion. This is done to keep the oil viscosity such that the oil can flow freely to the combustion chamber. Bunker C fuel oil is very thick and difficult to use without pre-heating.

The fire in an oil burning locomotive is controled with two valves: The fuel valve, which controls the flow of oil to the atomizer, and the atomizer valve, which controls the steam to force the oil into small droplets for burning.

The fireman must control the amount of steam, oil, and air in the combustion chamber to produce the most effecient fire to boil the water. The fireman observes the color of the smoke emitted from the smoke stack to determine what the fire needs. Thick, foul smelling black smoke indicates that the fire is not burning correctly due to too much fuel oil. The fireman can increase the draft of air using dampers and the blower or reduce the amount of oil to the burner. Blue smoke indicates too much steam is being admitted to the atomizer, and he must reduce the steam pressure. A light grey smoke indicates proper adjustment, while no smoke at all means the fire is too light and should be increased.

It is worthy to note that under some circumstances, the fireman can cause a series of hollow booms or small explosions though mis-adjustment of the fire. If one were to be watching with the firedoors open at such a time, one would see that the flame is being ripped away from the burner and into the flues. This also can cause heavy amounts of soot to be deposited in the flue, reducing the effeciency of the boiler. The soot can be cleaned by throwing sand into the combustion chamber, but this causes undesireable wear to the flues and any superheaters.

ReferencesEdit

  • Semmens, P.W.B. and Goldfinch, A.J. (2000). How Steam Locomotives Really Work. Oxford, New York: Oxford University Press. ISBN 978-0-19-860782-3.