How a steam railway engine works - the authorative text - boilers and fittings, firing, etc.

MUTUAL IMPROVEMENT CLASSES

STAGE 1

OPERATION OF LOCOMOTIVE TYPE BOILERS AND ASSOCIATED FITTINGS

COURSE NOTES*

6th May 2001

INTRODUCTION

It is intended that this short course will assist train crews to improve their operational skills on the foot plate by making them more aware of the capabilities of the boiler and to give a better understanding of the various parts and controls. The course will cover general boiler construction, boiler types and the various mountings attached to them with a description of their construction and correct operation. An explanation of the physical properties of steam and the physical and chemical properties of the principle fuels , coal and fuel oil. An explanation of the principles of combustion and the transformation of heat into power. A section on boiler water treatment , basic principles explained and a discussion on the effects of priming and foaming. The last section will deal with locomotive feed water injectors, types and principles of operation, together with some possible causes of injector failure.

THE LOCOMOTIVE BOILER

The requirements of a locomotive boiler are very exacting, it having to withstand high steam pressures with a large margin of safety, combined with efficiency and economy of space. The restricted space at the disposal of the designers, and the large area of heating surface required have determined the form of the boiler. The efficiency of a boiler is measured by the amount of water that can be evaporated per lb. of coal, and this depends on the quantity of coal that can be consumed on the firegrate. For the economical production of steam, therefore, a boiler must be well designed for its work and must be handled with a degree of intelligence.

TYPES OF BOILERS AND FIREBOXES

The boiler or steam generator consists essentially of the steel shell, which includes the boiler barrel, the outer firebox wrapper plate, back plate, throat plate and smokebox tubeplate. To this is fitted the inner firebox and steel flue and smoke tubes.

Diagram 1. Shows a design of boiler supplying saturated steam.

Diagram 2. shows a boiler for supplying superheated steam. The latter diagram illustrates a taper boiler, the cylindrical barrel is made in two sections with the larger diameter at the rear, were the barrel is joined to the outer firebox. The dome in this design, which houses the regulator valve and the auxiliary internal steam pipes, is positioned on top of the rear sloping section of the barrel, where it forms a collector for the steam above the surface of the water.

Fireboxes may be of the deep, long narrow type between the frames or of the shallow, wide type, for example, as fitted to 4-6-2 classes of locomotives. In the latter case the firebox is spread over the frames. The wide type of firebox is fitted when a large grate area is necessary.

The inner firebox is supported from the outer firebox by the foundation ring at the bottom, by crown stays at the top, and by palm stays between the firebox tubeplate and the boiler barrel. In addition, the firebox and outer wrapper plates, backplate and throatplate are stayed together with steel or copper stays, at about 4 in pitch. There are over a thousand of these stays in every locomotive boiler. Longitudinal stays are fitted between the boiler backplate and the smokebox tubeplate, and cross stays between the firebox sides above the crown. From the firebox tubeplate, the steel flue tubes, which may be anything from 1.1/2 to 2.1/4 in. diameter, pass through the boiler barrel to the smokebox tubeplate. When the boiler is fitted with a superheater, a number of large flue tubes (approx. 5 in. dia) are provided in which the superheater elements are positioned.

Some boilers employ the flat top or 'Belpaire' firebox, this being designed to give a larger heating surface and a greater steam space over the firebox. The other type in general use is the round top firebox fitted to earlier designs although these were preferred by the Eastern region of British Railways until the. end of steam.

It is normal practice in this country for the inner fireboxes to be made of COPPER The locomotives of the Southern region, (West Country & Merchant Navy classes) are, however fitted with steel fireboxes and thermic syphons which improve the circulation of water around the boiler. Diagrarn.3. shows a SR. Merchant Navy boiler with the thermic syphons.

Copper for the inner firebox is used on account of it being a very good conductor of heat, but more especially because of its ductility and suitability for withstanding the great fluctuations of temperature within the firebox.

THE SMOKEBOX

The smokebox is an extension at the front end of the boiler barrel, which together with the blast pipe and the chimney, forms the means of producing an induced draught to the air required for combustion of the fuel in the firebox. Apart from the chimney orifice it is airtight. Other fittings in the smokebox are; The superheater header (when fitted), main steam pipes to the cylinders, Blower and ejector exhaust pipes. On some locomotives, notably Western region types the regulator valve is part of the superheater header.

The spark arrestor.
This is fitted to the smokebox to prevent the emission of live ashes from the fire being ejected from the chimney when the engine is working hard. On some locomotives it is simply a mesh wire basket fitted between the blast nozzle and the base of the chimney known as the petticoat pipe, the larger particles being arrested and remaining in the smokebox to be removed by hand at the end of the day.

A more complex type of spark arrestor has been fitted to some locomotives that are used on Railtrack lines due to the more stringent spark emission regulations. This has a vertical diaphragm plate at the back of the smokebox that breaks up the larger pieces and then deflects them towards the front of the smokebox were the flow of air is much less , the ashes are then drawn through the wire net screen before being ejected through the chimney, by which time they are small, dead and harmless. (see diagram. 4.)  Photos illustrating the above notes

THE SUPERHEATER

The superheater is the part of the boiler designed to produce superheated steam, that is steam that is heated further after leaving the boiler and out of contact with the water from which it was generated. It is then fed directly to the cylinder valve chests. It consists of a steam collector or header for distributing steam from the boiler via the regulator valve to a series of small tubes called ELEMENTS which pass through the larger flue tubes and return to the header as superheated steam. The steam on passing through these elements has absorbed heat from the hot gases from the firebox on their way through the flue tubes to the smokebox and out of the chimney.

The superheater header is attached to the smokebox tubeplate at the outlet of the main internal steam pipe from the regulator valve and is placed horizontally across the top of the smokebox . At each side of the header are flanges for connection of the main steam pipes to the cylinders. (see diagram.4)

The Elements are fabricated from lengths of solid drawn steel tubing with three return bends, clipped together to form a bundle or element and are attached to the header with a ball and socket joint. These are known as "Melesco" elements after the company which designed them. (see diagram S.) The number of elements will vary with the degree of superheat required, however all the steam that passes through the regulator valve has to pass through the superheater elements before it can reach the cylinders.

THE BRICK ARCH

The brick arch as its name suggests is made from high temperature refractory material, and is constructed within the firebox . It extends from the tubeplate just below the bottom row of tubes and is inclined upward for just over half the length of the firebox.

Its purpose is to lengthen the path the hot gasses have to take allowing more complete combustion of the volatile matter given off from the fuel on the firebed. When the refractory reaches its normal temperature (white hot over 2500°F) from the radiation of the firebed this further assists in the combustion of the volatile matter given off by the fuel. Secondary air passing through the firehole door is directed under the brick arch by the deflector plate and allowed to mix with the gasses on the firebed and so improving combustion.

Lastly the brick arch allows the gasses to spread evenly over the tubeplate allowing the boiler to absorb as much heat as possible before being passed up the chimney.

THE FIREHOLE DOOR AND THE DEFLECTOR PLATE

Various patterns of firehole door are fitted to locomotives, these give access for firing and are a method of controlling the secondary air to the firebox. Large amounts of secondary air entering the firebox is harmful to the boiler and can result in leaking tubes and stays. This is partly prevented by the use of the DEFLECTOR PLATE or BAFFLE PLATE. This is a metal scoop formed to the profile of the firehole and extends for about 20ins into the firebox. It is inclined downwards on the same plane as the brick arch and should point under it. A deflector plate that points over the brick arch is totally useless and must not be used. Its principle purpose is to deflect the cold incoming air under the brick arch which is white hot and preheat the air whilst allowing the air to mix with the gasses on the firebed and so assisting proper combustion. As stated above it goes a long way to preventing cold air impinging on the boiler plates causing steep temperature changes and causing leakage. Finally in the serious event of low water level and a fusible plug melting the deflector plate will prevent serious eruption of steam back through the firehole door. A correct fitting deflector plate must always be in place when the boiler is in steam.

DROP GRATES, ROCKING GRATES AND THE HOPPER ASH PAN

Most of our locomotives are now fitted with drop grates and hopper ashpans and are far better than the older plain firebar grates, they are there to facilitate disposal of the fire. They are of various types but the most common being the BR STD. type These consist of hinged firebars which can be controlled from the cab by means of levers. See diagram.6. A two way stop and locking plate enables the grates to be operated with a limited amount of movement so as to break up the clinker when running, or to be rocked fully to enable the fire to be dropped completely at disposal. A hopper ashpan is provided on most locomotives and this has hopper doors at the bottom. The doors are held shut with a catch on the side of the ashpan and are operated with the same lever as the rocking grate. The loco must not be run with the doors open and care should be taken to see that the catch is secure before moving off shed. 1 The hopper doors should always be opened before dropping the fire during disposal so as to prevent the hot fire doing serious damage to the ashpan. This operation should be done over an ashpit or other authorized cleaning point. (see diagram 7)  Photos illustrating the above notes

DAMPERS

A large proportion of the air required for combustion is admitted below the firebars and so is referred to as PRIMARY AIR. This can be regulated by the fireman by means of dampers fixed into the ashpan in the form of swinging doors. There is usually one leading and one trailing damper and are controlled by levers in the cab.

The dampers should be operated in such a way as whichever direction the locomotive is travelling the opposite damper door should be used. Whenever the locomotive is about to enter a tunnel the dampers should be fully closed, the blower put on and the firehole doors closed to prevent a blowback.

BOILER MOUNTINGS AND BOILER CONTROLS

In addition to the boiler being of sound design and construction to be able, to withstand the forces of steam pressure within, certain safety features or safety devices must be. fitted to it to prevent the operating conditions becoming dangerous through over pressure or low water level. Both of these conditions could present a very serious hazard to anyone within a very wide area and in the event of a boiler explosion would cause catastrophic damage to the surrounding area.

On the next page, study the photographs taken in the aftermath of a boiler rupture. These pictures show what incredible forces are stored up within a locomotive boiler, and if allowed to get out of control and the boiler plates fail , anyone on the footplate would be killed instantly or at the very least, very badly scalded . Fortunately these incidents are rare nowadays due to more controlled inspections, however the locomotive boiler is still under full manual control and should be under constant supervision when in steam.

By way of another example to illustrate the enormous power stored up within the locomotive boiler, consider the following simple calculation.

The average locomotive boiler backplate is approx 60in wide and 84in high and the boiler pressure is, say, 2501b in.

60 x 84 = 5040 sq. inches

5040 x 250 = 1,260,000 lbs.

1,260,000 2,240 = 562.5 TONS

This is the steam pressure in front of you when you are stood on the footplate. Just something to consider when you are next booked out on a loco.

SAFETY VALVES

The safety valves are perhaps the single most important safety device fitted to the boiler. They are a mandatory requirement and are fitted to prevent the boiler pressure from exceeding the registered working pressure of the boiler. This is the steam pressure for which it was designed and is indicated by a metal tablet secured to the firebox backplate.

The "Ross Pop" type of safety valve was in extensive use on the former British Railways and it is still in use today. Below is a sectioned example as used on the former Midland region and on all the BR Std. Locomotives .

In this design, when the working pressure is reached, the spring loaded valve rises and admits a small amount of steam through the seat of the valve into the Annular Chamber, this gives increased lift to the valve against the pressure of the spring The steam then escapes into the body of the valve and escapes through the holes on the top cap. The steam, when escaping acts on the increased area of the top cap, forcing the valve open still further until such time as the pressure in the boiler has dropped slightly. The spring then overcomes the pressure of the escaping steam and closes the valve instantaneously with a "pop" action.

Blowing off is wasteful of steam and can be avoided by careful management of the fire and injectors. For example: On a large 4-6-0 locomotive, for each minute the safety valve is blowing there is a loss of water of approximately 15 gallons and a loss of fuel of approximately 10 lb.

A typical example of safety valve as fitted to many of the former Southern region locomotives: the diagram shows its operation more clearly.

WATER GAUGES

Probably the most serious condition any steam boiler can suffer, is low water level. The crown of the firebox must always be covered with water at all times when the boiler is in use. If it should become uncovered, even for a short time, the firebox roof will very quickly become red hot. When this happens the metal it is made of becomes soft and plastic, the steam pressure then forces it off the supporting stays disgorging the remaining steam and water contents into the firebox with violent force.

As it is not possible to see through the steel plates, some form of visible water indication is required, and this is performed by the water gauge. Diagram. 10. shows a typical tubular water gauge frame, this is fitted to the boiler backplate in the position shown. Two water gauges are almost always fitted in pairs on the front of the backplate. The exception is locomotives of the Ex. Western Region and Ex. WD. USA Types that were used in this country: these were fitted with only one water gauge and a set of test cocks. Two methods of checking the water level must be provided to check one against the other, and if one is put out of use through damage or it ceases to work properly the other one can be used.

The designs consist typically of a top steam cock "K', a bottom water cock 'V' and a drain or blow through cock "C". Cocks "X' and "B" are connected together with a glass tube called the gauge glass. Fitted around the gauge glass is a protector, which is made from thick toughened glass, this protects the glass from being damaged and also protects the train crew in the event of a burst gauge glass.

The water level in the boiler is shown inside the glass tube. With the boiler in steam THE WATER LEVEL MUST ALWAYS BE VISIBLE. With it showing in the bottom nut the firebox will still be covered. The Perforated plate behind the protector usually has on it a set of diagonal black fines , with NO water showing in the glass these black lines will appear the same. With water showing, the part that contains water will be refracted and the black lines will appear to show the other way round. This is one way to tell whether there is water in the glass or not (i.e. Completely full or empty).

HOW TO TEST THE GAUGE GLASS (Refer to diagram No.10)

The gauge glass must be tested at least once after taking over the locomotive and at regular intervals during the time that you have control of the boiler The important thing to remember when testing the gauge glass is that from the top cock "X' the steam should HISS. S. And from the bottom cock "B" the water should ROAR. When it comes out of the drain pipe.

HOW TO CHANGE A LEAKING OR BURST GAUGE GLASS

1. If the gauge glass bursts, throw a coat or sack over the effected fitting, and shut off the steam cock "X' and water cock 'M" instantly

2. Open the drain cock "C"

3. Remove the perforated backplate and remove the protector

4. Remove the top plug from the top fitting and remove the loose restrictor

5. Remove the gland nuts from the top and bottom fitting and clean out any remaining glass and rubber washers

6. Place the new glass in from the top (if possible) feeding the parts on to the glass as follows:

• Top rubber washer

• Top gland follower

• Top gland nut

• Bottom gland nut

• Bottom gland follower

• Bottom rubber washer

7. Push the glass firmly down into the bottom fitting

8. Feed in the rubbers, gland followers and finally screw up the gland nuts HAND TIGHT only

9. Replace the restrictor and the top plug in the top fitting

10. Refit the protector and the perforated back plate, and ensure it is secure

11. Warm the glass through by opening the steam cock "X' slowly

12. Slowly close the drain cock "C" (the glass may burst again)

13. Finally open the water cock 'S" and check the water level rises in the glass

NEVER REMOVE THE GAUGE GLASS PROTECTOR UNLESS THE PRESSURE HAS BEEN RELEASED FIRST

BOILER PRESSURE GAUGE

In order to detect the steam pressure within the boiler, a pressure gauge is fitted. This is a mandatory requirement and is always fitted directly to the boiler. A cock is usually fitted to allow changing of the gauge should it become defective. The design is always of the Bourdon tube type, it made from phosphor bronze. The dial has a scale and is usually marked off in Pounds per Square Inch. (LBf/in²) though sometimes it may have a dual scale marked in Bars, usually in increments of ten. On every boiler gauge there is marked a Red fine on the scale, this is the maximum working pressure of the boiler and the point at which the safety valves will lift.

FUSIBLE PLUGS

In order to give the fireman a warning and to some degree protect the crown of the firebox, One or more fusible plugs are screwed into the roof of the firebox. These are made from bronze and have a Lead core which will melt at quite a low temperature. If the water level drops too low and uncovers the plugs, the lead melts and allows steam to escape into the firebox. The hole the lead fills is only about 318 in. Dia. And so will not be sufficient to extinguish the fire. Should a lead plug "drop" , The injectors should immediately be put on and steps taken to remove or deaden the fire. An example of a fusible plug is shown in diagram. 12.

BLOWER VALVE AND RING

The blower consists of a perforated ring or pipe fitted round the top of the blast pipe and is connected to a steam supply from the boiler via a valve in the cab and is usually under the control of the driver. The function of the blower is to create a vacuum in the smokebox for the following;

1. To increase the draught on the fire when the locomotive is stationary, or in order to raise steam pressure.

2. To clear smoke.

3. To counteract back draught in the case of 3. Whilst working a train or light engine, the blower valve must always be opened prior to closing the regulator, or before entering a tunnel.

BLOWDOWN VALVE

In order to remove the contaminants of the boiler water which has allowed to settle as sludge at the bottom of the foundation ring, a Blowdown valve is fitted. When this is opened the boiler pressure forces out this sludge with violent but controlled force. Before operating the Blowdown valve the boiler water level must be high in the glass and have sufficient steam pressure to operate the injectors to be able to restore the water level when the valve is closed.

THE WATER LEVEL MUST NOT BE ALLOWED TO DROP OUT OF SIGHT IN THE GAUGE GLASS, AND MUST BE CONTINUOUSLY WATCHED WHEN BLOWING DOWN, WITH THE BOILER IN STEAM.

The operating handle should be secured when not in use to prevent tampering or inadvertent operation. Care must also be taken when sighting the locomotive for blowing down and a clear warning given to people nearby who may be scalded from the outlet pipe.

REGULATOR VALVE

The regulator valve is probably the biggest boiler fitting and is positioned usually within the dome of the boiler. It is operated by the handle in the cab, mounted on the backplate where it passes through a gland into the boiler. There are several types of valve all designed to provide a controlled passage of steam from the boiler through the superheater (if fitted) to the cylinders. The most common type is the Vertical Slide which has two, three or four ports on the valve (sometimes called Second valve), and two ports on the pilot valve (First valve). The pilot valve opens first when the regulator handle is moved which gives controlled starting. The main valve is forced onto its faces by the high steam pressure and so the pilot valve allows pressure to build up on the other side of the valve, equalising the pressure somewhat and making the main valve easier to open. An example of a vertical slide type regulator is shown in diagram. 13. The other types of regulator valve are: Horizontal slide type (fitted to many Ex LMS classes); the Double beat type (fitted to many Ex LNER classes); and the Balanced piston type which are fitted to all the EX SR West Country, Battle of Britain and Merchant Navy classes. Some types of regulator are fitted in the smokebox within the superheater header, (Ex GWR and BR Std. Britannia & clan).  Photos illustrating the above notes

MID HANTS RAILWAY
MUTUAL IMPROVEMENT CLASSES
STAGE II

3rd June 2001

HEAT AND STEAM, FUEL AND COMBUSTION, BOILER WATER TREATMENT

REGISTRATION (Record of course attendance.)

INTRODUCTION.

It is intended that this short course will assist train crews to improve their operational skills on the foot plate by making them more aware of the capabilities of the boiler and to give a better understanding of the various parts and controls.

The course will cover general boiler construction, boiler types and the various mountings attached to them with a description of their construction and correct operation.

An explanation of the physical properties of steam and the physical and chemical properties of the principle fuels, coal and fuel oil. An explanation of the principles of combustion and the transformation of heat into power.

A section on boiler water treatment , Basic principles explained and a discussion on the effects of priming and foaming.

The last section will deal with locomotive feed water injectors, types and principles of operation, together with some possible causes of injector failure.

....................

FUEL AND COMBUSTION.

COMPOSITION OF AIR AND COAL.

Combustion takes place when coal burns in air, and correct combustion can only be obtained by bringing the right amounts of coal and air together at the same time. To understand this more clearly, we have to look at the chemical constituents of coal and air. Coal varies in quality and composition, but a greater part of it consists of carbon, the remainder consists of the gases Hydrogen, Oxygen, Nitrogen and Sulphur the remainder is ash. (see Dia. 1) Air consists of a mixture of gases by weight of approx 23% Oxygen, and 77% Nitrogen.

COMPOSITION OF FUEL OIL.

By comparison the chemical constituents of bunker quality residual fuel oil that would be used in typical oil fired boilers is, Carbon, Hydrogen, Sulphur, Oxygen and Nitrogen together with small quantities of impurities such as Sodium, Vanadium, Nickel, and Chromium. The calorific heat value of fuel oil is more than coal being typically 19,000 btu/lb. The value for coal, (UK, European grades, 12,000 to 15,000 btu/lb.) The value for wood is about 7,000 btu/lb. And takes up five times as much space.

Combustion is the chemical combination which takes place between the constituents of fuel and oxygen when the fuel burns. The heat producing constituents of coal are Carbon and Hydrogen, heat being produced when these elements combine with oxygen from the air. Coal must be heated to above 450° F. before it commences to burn, but it must be.burnt at a much higher temperature before it will burn efficiently. The fuel requires a specific amount of Oxygen to burn completely, this gives off heat and Carbon Dioxide and water vapour. If there is insufficient oxygen or air supplied to the fuel, incomplete combustion will take place and Carbon Monoxide will be given off. When fuel is burnt in a limited supply of air only about 30% of the heat is produced. 1lb. of carbon completely burned to Carbon Dioxide produces 14,550 btu.s 1lb. of Carbon incompletely burned to Carbon Monoxide produces 4,350 btu.s That is about 70% of the heat is wasted.

The chemical elements that make up the constituents of coal are combined in a complicated structure, however they can be considered as consisting as two main groups. Part 1; Volatile (gaseous matter and tar oil ), which is the portion that is given off as a gas when the fuel is heated. Part 2; Fixed (solid ) Carbon, in the form of coke, which remains behind after the volatile matter has been given off. Volatile matter consists of many gaseous and liquid (tar) compounds called Hydrocarbons, these burn easily when released making lots of smoke and so requires a large proportion of secondary air to burn it completely. At high temperatures these hydrocarbons split up into hydrogen and carbon and are, burned to form carbon dioxide and water vapour, provided sufficient air is present. If insufficient air is present these hydrocarbons escape up the chimney unburnt in the form of black smoke. The sulphur content of coal is of little consequence as a heat producer. It is usually found in coal as Iron Pyrites, (Iron Sulphide), the sulphur burns out to form Sulphur Dioxide and Hydrogen Sulphide leaving the iron which melts and mixes with the ash to form clinker which welds itself to the firebars. A high percentage of Iron Pyrites in the coal will cause considerable clinker problems. Coals from Lancashire and Russia contain a great deal of sulphur. (1.7 - 5.0%) The Nitrogen content of coal is of no consequence. (usually 1.6 - 3.0%). The Nitrogen content of the air required for combustion , however plays a very important part in actual practice. 1lb. of coal requires 12lb of air for complete combustion of which 9lb of this is Nitrogen. The Nitrogen does not burn but restricts the rate of combustion and also has to be heated up and causes a considerable loss of heat. The loss is due to the high temperature at which the gases leave the chimney, approx 700-750° F, and the loss due to this is about 10%

WHAT HAPPENS IN THE FIREBOX.

Consider what takes place when fresh fuel is fired onto a white hot bed of burning coal in the locomotive firebox. Air is supplied to the firebox in two different ways, (1) PRIMARY AIR through the dampers in the ash pan and through the firegrate. (2) SECONDARY AIR supplied through the firehole. Volatile gases are given off at once and are quickly drawn through the tubes, and unless sufficient air is available for combustion they will pass up the chimney in the form of dense smoke. Volatile matter requires a considerable quantity of secondary air for it to burn completely. Volatiles contain a great deal of the heat value of coal and failure to provide the adequate air required will result in valuable heat losses. The fixed Carbon which remains after the volatiles have been given off, remains on the firebed until there is sufficient primary air to burn it and still sufficient secondary air must be provided to ensure that the Carbon is fully burned to Carbon Dioxide.

Heat losses can also occur through admitting more air than is required for combustion. This excess air does not take part in combustion and is heated up by the gases in the firebox and carried away forming more heat losses in the same way as the Nitrogen. It is however, necessary for about 20% excess air to be added to the firebox with any type of fuel, coal or oil. This is because thorough mixing of the air and combustible gases is difficult because of the high speed at which they pass through. If exactly the right amount were admitted then losses would occur due to incomplete combustion as a consequence. (see diagram 2)

PRINCIPLES OF GOOD FIRING.

The successful operation of any steam boiler is to regulate the firing rate, the fire and the height of the boiler water level at all times according to the work to be performed and to have full boiler pressure when it is required, without blowing off from the safety valves.

Coal and oil varies in content from different parts of the world; Good Welsh steam coal consists mainly of fixed carbon and little volatile matter and so needs more primary air and less secondary air. Good Yorkshire steam coal is high in volatile matter and requires a smaller amount of primary air but a great deal of secondary air through the firehole. By comparison Household coal has a lower heat value due to a high proportion of volatile matter and tar and sulphur impurities and so produces a large amount of smoke.

Coal will be economically burned when the firebed is of the right thickness. If the fire is too thick the air cannot pass through it. If too thin, excessive air passes through forming holes. In both cases the firebox temperature will be considerably reduced. If too much coal is added to the fire at one time, the amount of volatile matter given off will be so great that it will be impossible to provide enough air to burn it completely. Firing should be regulated so that the volatile matter has time to burn with the air that is available. This is possible by limiting the number of shovelfuls of coal put onto the fire at any one time. The whole of the volatile matter is not given off immediately the coal is fired and it is therefore necessary to wait before firing again. This is easily seen by closely watching the emissions from the chimney. Volatile matter requires an extremely high temperature for proper combustion, and this is one of the functions of the brick arch. To obtain the maximum amount of heat for the production of steam, the best method of firing is to limit the amount of coal put into the firebox at any one time and to fire again only when the last charge of fuel has burned away. Fire Sparingly - Work Systematically. This is the essence of a good fireman.

BLOWBACKS

With the engine steaming normally the rate of burning is steady and the gases are being passed through the boiler and out of the chimney. If this flow is momentary interrupted (i.e. When closing the regulator or entering a tunnel ), the gasses will try to find an alternative path to the source of air. This is usually through the firehole with serious risk to the crew being burned. Blacking out a fire through overfiring may cause an explosive blowback due to volatile gases re-igniting on the firebed. The blower must always be put on sufficiently to avoid a blowback, and black fires must be avoided. By more careful firing.

TRANSFORMATION OF HEAT INTO POWER

Heat is a form of energy; therefore, when coal burns in the firebox of a steam locomotive its heat energy is capable of being expressed in terms of useful work. The high temperatures attained in the firebox by combustion of the fuel varies and may reach as much as 2500° F. This heat is transferred to the water in the boiler through the heating surfaces, converting the water into steam, the steam in turn being led to the cylinders where it is transformed into mechanical energy and hence to the tractive power of the locomotive.

The state or amount of heat in the firebox is measured by its temperature and the unit of heat, known as, BRITISH THERMAL UNIT (B.Th.U.), This is 1/180th part of the heat required to raise the temperature of 1 lb. of water from freezing point to boiling point, ie: 32° F. to 212° F. or Heat required to raise 1 lb. water by 1° F. = 1 B.Th.U.

The heat is transmitted from the burning fuel by three ways. CONDUCTION; transferred from one body to another by direct contact, ie; hot gases from the boiler tubes transmit the heat to the water by conduction. CONVECTION; the transfer of heat by currents circulating in the boiler water by the metal surfaces it comes in contact with by convection. RADIATION; fire in the firebox gives off energy in the form of radiant heat, this is absorbed and transmitted to the water through the metal surfaces by conduction.

RELATION OF STEAM PRESSURE TO TEMPERATURE

When heat is applied to water to raise it to boiling temperature (212° F), any additional heat applied will result in the water turning into steam at atmospheric pressure (14.7 lb/in² or 1 atm.). Steam generated in a boiler, being enclosed, cannot escape, and if the application of heat continues, more and more water is turned into steam which, being elastic, becomes compressed, decreases in volume and increases in pressure. As the pressure of the steam on the surface of the water increases, so the temperature at which the water boils rises correspondingly. At atmospheric pressure 1 cu. in. of water when converted into steam occupies , 1,642 cu.in. or nearly 1 cu/ft. At 250 lb/in² the volume of 1 cu.in. of water converted into steam occupies only 110 cu.in. or nearly 1/15 its original volume at atmospheric pressure.

The average locomotive boiler contains about 800 - 1000 gallons of water which is approx 221,600 - 227,000 cu/in. and so this massive amount of stored energy is harnessed and available for work.

SATURATED STEAM.

The steam collected above the water in the boiler is called Saturated steam or "Wet" steam, this exerts in increasing pressure on its surface which resists the formation of steam bubbles rising to the surface and calls for additional heat energy in the water. The higher the steam pressure required the greater the amount of heat energy will have to be added to the water.

o Steam at Atmospheric pressure has a temperature of 212° F

o Steam at 85 lb/in² pressure has a temperature of 327° F

o Steam at 225 lb/in² pressure has a temperature of 397° F

o Steam at 250 lb/in² pressure has a temperature of 406° F

Continued heating of the water will increase its temperature and so its pressure will continue to rise with more water being evaporated at the same time until the action of the safety valves prevents any further increase.

SUPERHEATED STEAM.

If steam is further heated out of contact of the water from which it was generated, its temperature will rise, its volume will increase, but the pressure will remain as near the same as in the boiler. In this condition the steam is said to be SUPERHEATED.

The temperature of superheated steam at working boiler pressure ranges from about 600° F. to 750° F and is dependent on how the locomotive is being worked and the efficiency of the combustion taking place within the firebox. The steam would then contain about 300° F. of superheat above that of the Saturated steam from which it was generated.

The three main advantages of superheating the steam are that any entrained water in the saturated steam is converted into additional steam," Cylinder condensation losses are largely prevented due to its greater store of heat, and the Volume is increased allowing the use of bigger cylinders than with saturated steam. This increase in volume can be up to as much as 40% at a working pressure of 225 lb/in². As a result of this increase, the demands on the boiler to supply steam to the cylinders is considerably reduced, resulting in a considerable saving in water and fuel.

For maximum efficiency the highest possible superheat is required. However, at around 800° F and above, the superheat temperature will start to have an effect on the lubricating oil supplied to the cylinders, this being hot enough to crack or break down the oil and causing carbonisation leading to lubrication failure and seized or broken valves, pistons and rings.

BOILER WATER TREATMENT.

Any steam boiler can be expected to have a considerable life period provided that it is properly looked after. One of these basic maintenance requirements is the careful control of the boiler water chemistry. World wide experience has proved the benefits of a chemically clean boiler, and a locomotive owner can do much to prolong the life of the boiler by keeping it thoroughly clean both internally and externally and not subjecting it to rapid or frequent changes in temperature.

The water that is carried on the locomotive, the Feed Water, is generally supplied from the towns mains. This is essentially fresh water, however, it contains many impurities, and when fed into the boiler via the injector, these impurities become a significant problem. It is during the process of evaporation that these impurities are deposited on the heating surfaces as scale, remain in solution to attack the metal plates chemically, or are carried to the surface causing the effects known as Priming and Foaming.

The quality of towns mains water will vary according to location around the country, and it is sometimes termed Soft or Hard. Soft water contains much fewer impurities and so has less scale forming salts, however it is usually of an acid nature and this is damaging to the metal plates causing corrosion. Hard water is what we find in the southern region, this has many scale forming salts but is generally of an Alkaline nature and so protects the boiler plates from acid attack.

Hard water contains, Calcium and Magnesium Bicarbonates, and calcium carbonate, these are the principal soft fur scales that adhere to heating surfaces. Calcium and Magnesium Sulphate are also present and these are the principal Hard forming scales which become baked onto the heating surfaces and prove very difficult to remove once established. Scale on the heating surfaces is an excellent insulator of heat and a coating as little as 1/8" of an inch will increase the fuel consumption by as much as 20%. Large or thick coatings of scale will cause overheating of the firebox plates and these can then burn away causing thinning and buckling of the plates, leaking tubes and leaking stays. Oil on the heating surfaces is another excellent insulator and a coating of only a few thousands of an inch will be equivalent to about half an inch of scale.

DO NOT BE CONFUSED BETWEEN BOILER WATER ADDITIVE AND OILS LIKE DIESEL, THESE ARE OFTEN STORED IN SIMILAR DRUMS!

Chemically SOFTENING Hard water by passing it through a water softener will exchange the scale forming (calcium and magnesium ) salts into more soluble sodium salts (sodium bicarbonate) which decomposes to carbon dioxide when heated. These salts will remain in the boiler water and add to what is known as the Total Dissolved Solids content, or TDS level. This becomes more concentrated as the boiler evaporates more water.

SCALE PREVENTION.

In order to keep the boiler as free of scale as possible it is necessary to treat it. This could be done by feeding it softened water, but this can be costly. The other method is to treat it chemically. This is done by adding a pre-mixed chemical compound to the feed water in the tender tank. Both methods using softened water and chemicals can be used together with excellent results, but do require strict blowing down routines.

This chemical compound that is currently used is supplied by Freeston and Sons and is called "L4" . It is very dark brown/red in colour and has little or no smell. It contains a complex blend of Phosphates, Tannins and starch, these are designed to convert the calcium and magnesium salts to insoluble compounds and so form a chemical sludge before they can be deposited on the heating surfaces. This sludge falls to the bottom of the boiler and is removed periodically by blowing down and washing out.

CORROSION PREVENTION.

The boiler structure must be protected from the effects of chemical attack which will cause corrosion and eventual failure of its component parts. The feed water must be treated to make sure that chemical corrosion attack cannot take place. (see diagram. L) The ideal conditions for boiler water is mildly Alkaline, this then being able to mop up and neutralize any acids that that are fed into it. Sodium Hydroxide is a strong Alkali and a weak solution of this is blended to the boiler water compound and all though the water supply is alkaline in nature, (hard water areas only), the Sodium Hydroxide helps to keep the boiler alkalinity topped up. Soft water areas are by nature slightly acid and so require more of this chemical in its water treatment.

OXYGEN ATTACK.

Apart from the scale forming salts, the feed water is usually rich in dissolved Oxygen. Iron contained in the steel plates of the boiler will react chemically with oxygen causing rapid corrosion, this is accelerated as the temperature and pressure gets higher. To prevent Oxygen attack Oxygen must be removed from the water, and this can be done chemically by the addition of an Oxygen Scavenger. This is blended into the boiler water compound. Sodium Sulphite is the commonest of these and as it reacts with the oxygen it forms a soluble non scale forming salt and remains in the water adding to the Total Dissolved Solids level.

TOTAL DISSOLVED SOLIDS.

The addition of feed water, with its dissolved salts, scale prevention, anti-corrosion and oxygen scavenging chemicals is being constantly added to the boiler and the pure water is being evaporated away, these chemicals and salts remain in the water, concentrating all the time. this is the Total Dissolved Solids content.

PRIMING AND FOAMING.

Continued increase in the TDS levels may reach a concentration where another condition known as FOAMING may result. The effects of foaming can be serious as the water will foam up in the boiler and be carried over with the steam depositing the salts in the superheater and causing the water to pass into the cylinders causing serious damage. Blowing down will reduce the effects of foaming by removing the dissolved salts from the water. Continued Priming and Foaming is an indication the boiler is in need of a washout. The boiler water compound contains a small quantity of a chemical called Polyamides or Antifoams, this reduces the film around the steam bubbles causing them to collapse more readily and so helping to prevent foaming occurring. In cases of severe contamination separate Antifoam compound may be added in addition to the boiler water compound.

PRIMING, which is the carry over of boiler water to the cylinders, is likely to occur when the TDS levels are high making the water more unstable and is more likely to occur running with a high water level, and a heavy steam demand allowing the water to easily be carried over. OIL contamination in the water will cause severe priming and all steps to prevent oil entering the boiler water spaces and feed water must be taken.

MID HANTS RAILWAY, MUTUAL IMPROVEMENT CLASSES.

STAGE III. 1st July 2001

LOCOMOTIVE FEED WATER INJECTORS

INTRODUCTION.

This last section will deal with locomotive feed water injectors, types and principles of operation, together with some possible causes of injector failure.

LOCOMOTIVE FEED WATER INJECTORS.

THE PRINCIPLE OF THE INJECTOR.

The injector is a device for delivering feed water to the boiler. The earliest form of injector was invented by a Frenchman named Henri Giffard in July 1858 and patented by him. It was fitted to locomotives to replace unreliable steam pumps and axle driven pumps. The design, though extensively modified, has survived up to the present day. In its simplest form it embodies three essential cones; (see diagram. 1.) The STEAM cone, the COMBINING cone and the DELIVERY cone.

The STEAM cone admits steam at boiler pressure to the injector, and by its shape increases its velocity. (about 1,700 ft/sec. Or 1,600 mph.) at this speed it is admitted to the water space and comes in contact with the water around its tip.

In the COMBINING cone the water quickly condenses the jet causing a partial vacuum. This vacuum draws in more water and carries it forward increasing its momentum. (about 131 ft/sec. Or nearly 90 mph.) The Combining cone is convergent in shape, and at the inlet is a mixture of steam and hot water and at the outlet is a solid jet of hot water.

Between the combining cone and the delivery cone is a gap known as the OVERFLOW GAP, through which excess steam and water are allowed to pass during starting up.

The DELIVERY cone is the last cone and is divergent in shape, when the water passes into this cone at very high speed a sudden decrease in speed is imparted and this causes its pressure to rapidly increase, sufficiently to overcome the boiler pressure holding down the clack valve and enter the boiler. The injector is a device which causes energy changes, therefore; The change from pressure energy to velocity energy is brought about in the Steam cone. The complete combination of the steam and the water into the solid jet by the condensation of the steam, is the transference of its energy to the water and is brought about in the Combining cone. The Velocity of the water jet is rapidly decreased and converted into pressure energy on its entry to the Delivery cone. The temperature of the water is increased by about 150° F. on its passage through the injector. The early injectors described above proved difficult to start and were unreliable when used on locomotives, due to the vibration, set up whilst running, affecting the combined jet of water and steam on its passage from the combining cone to the delivery cone. Modern injectors are designed to overcome this difficulty and automatically restart should they inadvertently "Knock Off".

The types of modern injectors now described are called LIVE STEAM INJECTORS, because they rely on a live steam supply directly from the boiler to the steam cone.

TYPES OF MODERN LIVE STEAM INJECTOR

Modern injectors overcome the difficulties of knocking off and vibration in various ways. Diagram.2. shows a modern injector that has been fitted to EX. Western region and EX. BR. Std. Designs. It works in exactly the same manner as described previously, the distinct difference is in the combining cone. The upper portion of the combining cone is formed by a hinged flap, and the vacuum developed in the combining cone, when the injector is working, holds this flap against the fixed portion forming one continuous cone. If the action of the injector is interrupted or the jet upset, the vacuum in this cone is destroyed and the resultant pressure forces the hinged flap open, allowing any steam and water to escape through the overflow pipe. When the pressure has been relieved the vacuum rapidly re-establishes itself and the injector will automatically re-start. This type of injector is often referred to as the HINGED FLAP type.

The next type of injector is shown in diagram. 3. This type was fitted to large numbers of EX. London Midland region types. This too works in exactly the same way as previously described, and again, the difference is in the design of the combining cone. In this arrangement the combining cone has a Fixed and Movable portion. The steam along with the feed water, during its passage through the combining cone, is fully condensed causing a high vacuum, this causes the moving portion to be held onto the seat of the fixed portion, forming in effect one continuous cone. If however, the action of the injector is interrupted or the jet is upset, the vacuum in the cone is destroyed and the resultant pressure forces the movable portion off its seat and allows any steam and water to escape to the overflow pipe. When the pressure has been relieved, the vacuum is rapidly re-established and the injector will restart, the movable portion of the combining cone having taken up its normal working position. This type of injector is often referred to as the MOVING CONE type.

The last type of live steam injector is shown in diagrams, 3 and 4, being of a similar design, and is known as the "Monitor" type. This was extensively used on locomotives exported to all parts of what was the British Empire, on EX. London Midland region, later classes and on the EX. Southern region, Merchant Navy, West Country and Battle of Britain classes, and produced in several sized capacities. This type of injector still works on the same principle, but with these differences; The steam cone has two parts and the combining cone has no moving parts but is fitted with slots. When the water is turned on the water passes into the combining cone and through the slots to the over flow. When the steam is turned on it is directed in two jets, the primary annular jet and the secondary forcing jet. The primary jet, on leaving the steam cone, comes into contact with the feed water and forces it down the combining cone passed the end of the secondary inner steam cone, at which point the second jet of steam is introduced which gives further impulse to the combined jet. The combined jet flows through the combining cone where condensation is completed and then enters the delivery cone and so to the boiler via the clack valve.

Should interruption take place causing the injector to "knock off", the steam and water escape through the slots in the cone to the overflow, until the jet is reformed by the condensation of the steam and the injector restarts automatically. This type of injector is often referred to as the SLOTTED CONE type.

These are the most common of the live steam injectors likely to be encountered today, there are several, mostly older types, like the Backhead water lifting injector, The Gresham hot water combination injector and the Metcalfe hot water injector. They all work on similar principles.

SECONDARY CLACK VALVES

Most injectors, on their discharge flange are fitted with an additional check valve to safe guard the possibility of the main boiler clack getting stuck and releasing the contents of the boiler through the injector overflow pipe. The feed pipe also contains a considerable amount of water, and this check valve helps to prevent feed water from draining back down the pipe and through the overflow pipe to waste, when the injector is shut off.

OVERFLOW VALVES

On diagrams 2, 4 and 5, you will see that the overflow pipe is fitted with a check valve, this allows water to flow freely out of the injector but will not allow it to flow back the other way. This device is fitted to prevent the ingress of AIR to the injector when it is working. When the jet is established, a high vacuum is developed and this will pull in a great deal of air, which will combine with the feed water and enter the boiler. As has been said on the section on water treatment, that air contains OXYGEN and this is responsible for corrosion of the steel boiler plates. This check valve prevents the ingress of air to the feed water and prevents it entering the boiler. Some injectors have ferrules fitted to the overflow pipes for the purposes of filling the boiler. You should check that they either, do not have an overflow valve fitted , Or, that the overflow valve is held in the open position ,(usually by a chain and pin to the spindle) during the filling operation. You should make sure that the overflow valve is operational again after filling the boiler.

THE EXHAUST STEAM INJECTOR

One of the ways to overcome the inefficiency of the steam locomotive has been to utilise some of the waste steam from the cylinders (which still contains a considerable amount of heat) that would otherwise escape up the chimney. Some of this steam could be used to heat the feed water before it enters the boiler so less fuel would have to be burned to heat this before it was turned to steam. The action of forcing water into the boiler also uses energy from the fuel and so the exhaust steam is also used for this purpose. These energy changes are brought about in the EXHAUST STEAM INJECTOR.

Exhaust steam injectors are usually only fitted to the larger locomotive types, as the benefits from using large amounts of exhaust steam are only available when the regulator is open and the boiler working at a high output for long periods. 100 gallons of water would require massive amounts of exhaust steam to heat and force it into the boiler. It has to be remembered that the exhaust steam is at quite low pressure, around 20 lb/in². or less and this has a temperature of about 260° F. it is also seven times its original volume at boiler pressure of 250.lb/in². and 406° F. It is possible to attain feed water heating at a temperatures up to 230° F. and the economy of fuel realised would be from 8 to 12 %. The exhaust injector introduced and patented by Messrs "Davies & Metcalfe Ltd.", has established several types which are all still in use today. These are; class H, J, H/J, and the class K, improved , types. All of these types have an automatic changeover from exhaust steam to live steam should the regulator be closed and the supply of exhaust steam cut off, this will keep the injector running without any attention. The H, and H/J types are both fitted with a steam controlled water valve which is automatically opened when the injector steam valve is opened, making these injectors very simple to operate and less wasteful of feed water. From a careful study of the sectioned diagrams the differences between the types can be seen.

PRINCIPLE OF OPERATION

The exhaust injector is fitted with some additional cones to enable it to work at the lower pressures, with reference to the diagram of the class H injector, the first cone is the Supplementary steam cone, which gives initial momentum to the exhaust steam and is necessary as the exhaust steam alone is insufficient to make it operate efficiently. The next is the Exhaust steam cone, first admitted through a central cone where it meets the feed water through an annular jet. The exhaust steam is condensed and imparts momentum to the water, and the mixture of steam and water flows forward at high velocity through the next cone called the Draught tube. A high vacuum is created within this tube at the end of which a second supply of exhaust steam is admitted in the form of an annular jet, thereby giving further momentum to the mixture, and this, passing through the vacuum tube enters the Combining cone where condensation is completed and the energy available in the steam utilised in its entirety to impart velocity to the water jet. The latter finally passes through the divergent Delivery cone, thus converting the energy available from Kinetic to pressure form, and thence to the boiler clack valve and into the boiler.

PRINCIPLE DIFFERENCES BETWEEN THE CLASS "H", "J", "H/J" AND "K

The "J" type exhaust injector differs from the "H" type in the following; the two pivoted exhaust steam valves in the "H" type are replaced in the "J" type by a double-beat spring loaded valve fitted vertically and controlled by a steam piston below the valves. The automatic shuttle valve or change-over valve, is fitted below the "J" type injector with the addition of an automatic choke valve to regulate the quantity of auxiliary steam supplied to the injector when the regulator valve is shut. In the "J" type the automatic water control valve has been replaced by a manual operated disk valve on the body of the injector or above the water entrance to the nozzles. The disk valve is fitted directly onto and worked by the water regulator spindle and rotated by it. The water valve merely acts as a water admission valve and does not regulate the quantity of water admitted into the injector cones, which is controlled by the moveable exhaust steam cone as in the "H" type injector. To shut off the "J" type injector the steam valve is closed and the water regulator spindle moved to the shut position. In the "H/J" type the automatic water valve as on the "H" type is fitted to what is otherwise a "J" type injector. The "K" type of exhaust injector is the latest design and is fitted to the larger B.R. standard design of locomotives. In this design the moveable exhaust steam cone, which has previously been used to control the amount of water delivered by the injector, has been replaced by a fixed exhaust steam cone and the water supply controlled by a variable water valve which is separate from the exhaust injector body but connected to it by an intermediate feed water pipe. This arrangement enables both the injector and the water valve to be placed in accessible and convenient positions. The "K" type combining cone differs slightly from the previous designs in that addition to the hinged overflow flap there are two overflow slots.

HINTS ON THE USE OF THE EXHAUST INJECTOR

The automatic change-over valve is controlled via a pipe from the steam chest, if the locomotive is being worked lightly there may be insufficient steam pressure to operate it, or it may open and close intermittently causing the injector to fly off.

OR the change-over valve may open the exhaust steam valve, but there may be not enough exhaust steam pressure to operate the injector.

OR during shunting operations when the regulator is being opened and closed frequently.

OR if at say the summit of a climb and power is being reduced.

All of these conditions could cause the injector to fly off or operate erratically and so some forward thinking on the fireman's part and avoid using the injector at these times will ensure little trouble is experienced in its operation. To ensure that the exhaust steam is free from oil from the cylinders, a grease separator is fitted in the exhaust steam pipe. There is a small drain at the bottom of this which occasionally becomes blocked, this should be proved clear when preparing the engine.

© Andy Netherwood 2001

*Notes:  

• This  page reproduces notes written by Andy Netherwood, handed out at his courses in May and June 2001

• Diagrams used on the course were standard ones to be found in most works on the subject.  Only an essential one is reproduced here.  Photos

• Please forgive any OCR errors I've missed