Motors and Motor-Driving/Chapter 12

by Alfred Charles William Harmsworth

CHAPTER XII

STEAM CARS

By H. Walter Staner, Editor of 'The Autocar'

A steam car, although driven by a steam engine, really derives its power from heat, but, instead of the combustible or fuel being burned and converted into pressure in the cylinder of the engine, as in the internal combustion engine of the petrol car, it is burned under a boiler. The expansive or elastic force of the steam pressure generated by the heat of the fire in its turn drives the engine, which gives the car its motion. The heat energy of the fuel is released by combustion; this heat is used to generate steam in the boiler, and the energy of the steam is transformed into motion after being admitted into the engine. Thus the three main essentials, of the propelling apparatus of a steam car are the fire or burner, the steam boiler or generator, and the engine.

Fuel.—Coal or coke is not used for pleasure cars, as either is too cumbersome and dirty, and the fire requires constant attention, liquid fuel in the form of petroleum (paraffin), or petroleum spirit (petrol or motor spirit), being universally adopted. Although petrol will ignite instantly if a match be applied to it, and paraffin will not, both must be vaporised or transformed into a gas by heat before they can be economically and cleanly used as heating agents. Not only so, but when vaporised, they must be burned mixed with air on the Bunsen principle.

Examples.—An ordinary domestic gaslight is produced by burning gas in air, but the atmospheric or Bunsen burner burns a mixture of gas and air in air. Petrol Burners.—Assume for a moment that the petrol for the burner has been vaporised (method to be described later) and transformed into gas, which we will for the future call 'vapour.' The Locomobile burner (figs. 1 and 2) takes the

Fig. 1.—Plan View of Burner of a Locomobile

form of a shallow circular metal box about one and a quarter inch deep, and of slightly less diameter than the boiler under which it is placed. There are 107 half-inch tubes, which pass through the bottom and top plates of the box. In the top

Fig. 2.—Section of Burner

plate twenty small holes are drilled round each of the half-inch tubes, and as the vapour is injected into the box at the pipe a it passes up these small holes round each of the air-tubes, mixed with the air continually sucked in with it as it enters from the vapour nozzle, and it issues from the twenty small holes round each air-tube, and burns with a solid blue flame above the top plate of the burner, the air for combustion of the mixture (air and vapour) being supplied through the 107 half-inch

M. Serpollet on his first Steam Tricycle (coal-fired) (date 1887)

air-tubes. The tube a at the side of the burner, which is about one inch in diameter, is open at the outer, as well as at the inner end, so that the vapour which is injected into it induces a continual flow of air with it into the burner. The end of the vapour tube which projects into the induction tube a is called the nozzle or nipple. The burners of the Weston, Milwaukee, and many other American cars are practically similar to the Locomobile, and so is that of the Reading, but in this latter burner the vapour is injected from the centre of the bottom plate, so that the half-inch air-tubes have no break in their disposition, and if the petrol be inadvertently left turned on, there is no chance of it flooding the burner and being ignited when the burner is lighted, as it runs out on to the ground.

Vaporising the Fuel.—The petrol is forced from the petrol tank to the burner by air pressure, a cylindrical vessel is connected with the petrol tank, and it is pumped to about 45 lbs. pressure in the Locomobile and most cars of similar type. The pressure is obtained by means of an ordinary bicycle pump, and it occasionally requires a few strokes of the pump to maintain it as the petrol is used up. An air-pump driven by steam can be fitted to the Locomobile, so that the hand-pump need not be used. To vaporise the liquid, it is passed by means of a tube up through the boiler across the top of it, and down again through another tube, the heat of the boiler being found sufficient to transform the liquid into gas. Thence it passes into the burner. This is the Locomobile arrangement. In the Weston the petrol is pumped through a tube which runs straight across the fire-box, or circular case containing the burner, the heat of the fire vaporising it. In the Reading it is passed in tubes through the boiler once, and also over the fire. It will be seen that these methods, which are mentioned as examples, all require that the burner shall be in operation before the process of vaporising can be commenced, and as the burner can only consume vapour, some additional method is necessary to obtain the initial heat.

Starting the Burner.—The Weston starting apparatus is fed by a separate tube from that which supplies the main burner. Its working is as follows:—The tap a (fig. 3) is opened so that the petrol flows through the tube f, and by opening a small tap b the spirit runs into a little square box, outside the fire-box by the pipe f¹. In this box, g, is a small cup, and as soon as it is full it runs over and the tap it is closed. A match is then applied to a hole in the side of the box g, and the petrol in the small cup lighted; it burns under a tube of Г shape filled with copper borings and heats it and them. This Г has a tap c to it, so that petrol can be injected through it, and when it is heated the petrol, as it percolates through the hot copper borings, is vaporised. As soon as the petrol in the cup is nearly burnt out, the tap c is turned, which admits petrol from the pipe f into the Г tube burner above the cup. The flame of the petrol left in the cup lights this 'pilot burner,' and it projects its flame on to the vaporising tube across the fire-box, which supplies petrol to the main burner. When this is believed to be heated sufficiently to vaporise the petrol it can be tested by turning the tap d,

Fig. 3.—The Western Apparatus lor Starting the Burner

when, if the fuel is not vaporised, liquid will issue from the tap d¹, and a minute or two longer must elapse before the main burner can be started. As soon as gas is found to issue from d¹, e is slowly opened, and this admits the vapour into the main burner. It issues into the fire-box, and is ignited by the pilot light. As the heat increases the petrol tube across the fire-box becomes sufficiently hot to vaporise the full supply of fuel, and steam is raised. The pilot light burns continuously, so that when running down-hill or when leaving the car, the main burner can be turned right out; as the pilot light is always burning the burner can be relighted instantly as soon as petrol is turned on again. In the Locomobile the initial heat is usually obtained by a U tube, which is separated from the car, and has to be heated in a fire or gas flame. It is then put into the fire-box and screwed up to the petrol pipes so that the petrol passes through it to vaporise it before it is admitted to the burner. The burner is then lighted, and as soon as the boiler becomes hot enough to vaporise the petrol, which, it will be remembered, is passed through it, the firing iron, as the U tube is called, can be disconnected. This arrangement can now be dispensed with, and in place of it a small Bunsen burner is placed at the side of the fire-box, playing on a coiled tube, through which the petrol passes on its way to the burner. When this coil is heated the small starting burner, which is on a hinge, is turned away from it, but acts as a pilot light, so that the main burner can be almost turned out when stopping or running down hill.

Fig. 4.—Automatic Fire Regulator

The Automatic Fire Regulator.—Many steam vehicles are fitted with an automatic fire regulator, of which the Kelly fitted to the Milwaukee is taken as an example, and it is the same in principle as most others. Fig. 4 is a section of the device. A diaphragm or circular plate is pressed by the steam from the boiler, and as the pressure rises the diaphragm is, so to speak, bulged. In its turn it pushes the plunger rod, which has a conical head a, forward, so that it closes or partially closes the end of the tube b, through which the vapour passes into the tube c on the way to the burner. When there is no pressure in the boiler the coil spring round the plunger rod holds it back, so that the orifice closed by a is fully opened and the vapour passes freely into c and on to the burner. As steam pressure rises the diaphragm is gradually bulged, so that a commences to close b, and at a predetermined pressure, obtained by adjusting the screw d, it closes b entirely, which only commences to open again as pressure falls. When no constantly burning pilot light is used, there is a small groove cut in the opening b, so that a never completely closes it, and enough vapour is admitted to keep the main burner just alight. In some cars no automatic regulator is used, the fire being controlled entirely by the driver from the seat. It should be understood that although the automatic regulator prevents vapour passing to the burner when a maximum predetermined pressure of steam in the boiler is reached, there is always a tap in reach of the driver which enables him to turn off the supply of fuel at any time.

Paraffin Burners.—For burning paraffin instead of petrol, burners of a somewhat different description are employed, as paraffin requires more heat to vaporise it sufficiently, and when vaporised a larger supply of air is necessary for complete combustion. If these conditions are not obtained, a paraffin burner will smoke and give off insufficient heat. Clarkson's paraffin burner is shown (figs. 5 and 5a). In this the paraffin is forced by air pressure through the vaporiser, which takes the form of a coiled pipe above the flame of the burner. It then passes through the vapour pipe to the jet nozzle, and air is admitted by the door of the mouthpiece, and mixes with the paraffin vapour, which rushes along the inducing-tube and issues from the circular opening below the cap, where it ignites so that a spreading ring of flame is formed, which jets out all round the coiled ring of nickel wire shown in the figure; this and the shape of the circular trough tend to spread the flame, so that it completely covers the bottom of the boiler. The intensity of the fire is regulated by a control lever connected to a handle by the side of the seat, and it will be seen by examining the connections at the bottom of fig. 5 that the needle which increases or decreases the size of the hole of the jet nozzle. by which the vapour enters from the vapour-pipe into the inducing-tube, also proportionately raises or lowers the cap, so that the

 

Fig. 5—Section of Paraffin Burner

 

of the burner itself around the cap is proportionately adjusted in size. Air is supplied by suitable holes in the bottom of the fire-box. To obtain the initial heat, methylated spirit is poured into the circular trough and lighted, thus heating the vaporiser, or when gas is laid on in the stable a flexible tube and gas-jet can be used. The primary reason that the vapour

Fig. 5a.—Paraffin Burner (end view)

from the jet nozzle flows up the inducing-tube is because the heat of the fire-box induces a constant inward current of air through the open door of the mouth-piece. No automatic regulator is fitted to this burner, which is in the usual way controlled entirely from the seat, but the makers have designed a special form of diaphragm regulator, which is sometimes used, and when the burner is applied to a flash boiler, a regulator is employed, which is called the thermo regulator, by which the supply of vapour to the burner is automatically controlled by the temperature of the superheated steam. For explanations of 'Flash boiler' and 'Superheat,' see 'Boilers.'

The Syndicate vaporiser is an arrangement which permits paraffin to be burned in petrol burners of the Locomobile type. It consists of a vaporising coil heated by a suitable wick lamp, and to ensure a sufficient supply of air being mixed with the vapour a small jet of steam blows into the burner from the boiler by the side of the vapour nozzle, and so sucks sufficient air into a type of burner which would not otherwise supply enough for satisfactorily burning paraffin vapour. The arrangement was described and illustrated in 'The Autocar,' of January 18th, 1902.

The Serpollet burner shown in fig. 9 has a number of small atmospheric burners, and the paraffin is vaporised by being pumped in a tube across the fire-box before entering the burners. The initial heat is obtained by a gas-flame, or by burning alcohol in a tray under the vaporising tube. The burners are concentric; the vapour passes up a central tube surrounded by two air-tubes, and the suction of the vapour draws air up these, and it mixes with this air before burning.

The Boiler.—We have seen how the mission of the burner is to supply heat to the boiler, and how that heat is generated and controlled; the next step is to consider the generation of steam in the boiler. The duty of the boiler is to supply high-pressure steam to the engine. Steam is the gas which water gives off at boiling point, 212° Fahr. High-pressure steam is steam which is confined in a space smaller than that which it would occupy at atmospheric pressure. The smaller the space in proportion to the volume of steam, the greater the pressure. Steam so confined has immense elastic and expansive force, and the boiler and burner are so proportioned that when the pressure of steam is once obtained, the continual generation of it is so rapid that, although the engine is using it up all the time, pressure is maintained.

Fig. 6 is a photograph of a Locomobile boiler, and fig. 7 shows it partly in section. The boiler is a cylindrical vessel or drum, which should be kept rather more than half filled with water. Through the boiler some three hundred half-inch

Fig. 6.—Vertical Multitubular Boiler

copper tubes run, so that heat from the burner, after heating the bottom of the boiler, passes up these tubes, heating the water in the boiler. In the section it will be seen that the barrel of the boiler is strengthened by winding with piano wire, which is closely wound around the boiler in the same way that a gun is wire-wound. The rough coating of asbestos, or lagging, as it is called, is held to the boiler by thin metal bands. Its mission is to, as far as possible, prevent the escape of heat, as any loss of heat means that more fuel must be burned to maintain steam.

As the heat passes up the boiler tubes, after heating the bottom of the boiler, the water is heated and boiled, and the steam rises, filling the space between the water-level and the top of the boiler. This space is very much less than the steam would naturally occupy, and, consequently, pressure soon becomes high. The heat from the fire in the boiler tubes not

Fig. 7.—Locomobile Boiler with Main Burner in Position

only boils the water around the portion of each tube surrounded by water, but in the upper part its heat tends to dry the steam and keep it from being too wet for satisfactory use in the engine.

The hot gases then pass into a box on the top of the boiler, called the 'smoke-box,' and thence into the down-take, or chimney projecting below the car. The steam from the boiler passes along the pipe to the throttle-valve to engine, the handle of which is by the side of the driver, and as this throttle is open or shut, steam is admitted or shut off from the engine. The type of boiler we have been describing is fitted to nearly all the smaller and lighter steam carriages, though in the majority of cases steel enters more largely into the construction of the boiler, so that the wire winding is not used.

Boilers with tubes surrounded by water, up which the heat of combustion passes, are known as fire-tube boilers, and are the same in principle as those used on a railway locomotive, though in the latter case the boiler is horizontal, instead of vertical. There is another type of boiler which is largely used on steam lorries and other heavy steam automobiles, which is known as the water-tube type. In this the water is contained in tubes, which the fire surrounds—the Fig. 8.—Section of Toledo Boiler exact opposite to the arrangement in the fire-tube boiler.

Fig. 8 is a section of the Toledo boiler, which is a combination of the two types, as an internal chamber is surrounded by water and filled with heat from the burner, but to increase the heating surface a coil of spiral tube is introduced, starting near the bottom of the water, and passing up into the steam space. This induces a very violent circulation of the water, and, although only one coil is shown, eight are actually used, so that the central vessel of the boiler is almost filled with these coils. All boilers are fitted with an automatic safety valve, which releases surplus steam long before the pressure can become dangerously high. The way in which the boilers are supplied with water will be dealt with later.

The Flash Boiler.—All fire-tube and water-tube boilers carry a considerable quantity of water, but the flash generator is not a boiler at all in the ordinary sense of the word, and contains practically no water. So far as steam generation is concerned, the principle of the flash boiler may be likened to dropping water on a red-hot iron. A small stream of water is pumped through a coil of tubing, and this tubing is heated to an intense heat by the burners, so that almost as soon as the water enters it, it is 'flashed' into steam—that is to say, the process of boiling and steam generation is all gone through in an instant, and the water which enters the coil of tubing at the bottom issues from the top of the coil as high-pressure super-heated steam. This process goes on continually as long as the water is pumped into the coil, as its quantity is always small compared with the length of heated tube.

Figs. 9 and 10 illustrate the Serpollet generator and burner, the latter being dealt with under 'Burners.' The generator

Fig. 9.—The Serpollet Generator with burners below

Fig. 10.—Plan of Serpollet Generator, showing arrangement of coils

consists of a box with an outer and inner metal skin packed with asbestos to retain heat. Coils of round nickel steel tube are passed through the boiler, and fig. 10 is a plan of one of these coils. The coils are placed one above the other in varying numbers, according to the power of the engine they are required to drive. They are connected to each other by ɔ tubes, these junctions being outside the burner space, so that they do not get the direct heat of the fire upon them. It will be understood that these coils are arranged like shelves inside the generator case a (fig. 9) in the space b, with the burners giving off their heat below. The burners quickly bring the coils to a red heat, and a small stream of water is pumped into a (fig. 10), and almost instantly converted into steam. It passes right through the coil, issues at b into the next coil above, and so on to the engine. The upper coil superheats the steam—that is to say, it makes it very much hotter than it would be in either of the types of boilers we have previously described—as after being converted into high-pressure steam in the lower parts of the coils, it is still subjected to great heat in the upper lengths of the coil before it passes to the engine. The expansive force of the steam is considerably increased by this superheating, and not only so, but it is very different from the steam from a fire-tube or water-tube boiler, being much drier, as well as hotter, c (fig. 9) indicates the air-inlet to burner box, and the arrows show the direction of the air currents. d is the chimney.

Pumps.—When steam is up, and the burner in full operation, the water in the boiler is quickly evaporated, and the renewal of the supply is performed by pump. The pump is usually driven off the cross-head, a part of the engine which has a constant up-and-down motion. On most of the smaller cars the water supply is carried in a horseshoe-shaped tank at the back, which half encircles the boiler. In the Serpollet the water-tank takes the place of the motor bonnet of a petrol car.

The pump, fig. 11, has a tightly fitting plunger, which is pulled up and pushed down by the engine. As it makes its upward movement it sucks water in on the right, and the flap valve, which only opens in an inward direction, freely admits the water. As the plunger is pushed down it compresses the water, which at once closes the valve on the right and opens the one on the left, forcing the water to the boiler. The valve on the left is opened by the pressure of water from the pump and closed by the pressure of steam on the other side from the boiler as soon as the down-stroke of the pump ceases. Fig. 12 shows the form of pump more commonly employed on steam cars, which works on exactly the same principle as fig. 11, but, instead of the valves being of the flap or hinged type, they take the form of conical stoppers fitting into conical holes in the inlet and delivery sides of the pump.

Before the water from the pump enters the boiler, it is usually passed through a coil of tube inside the silencer or muffler, which is a cylindrical case, into which the exhaust steam from the engine is passed before escaping into the chimney. The expansion of the steam in the silencer reduces the noise of the exhaust, and the steam with which it is filled heats the coil through which the water from the pump passes to the boiler, so that the water itself is partially heated when

Fig. 11.—Pump with Hinged Valves

Fig. 12.—Pump with Conical Valves

it enters the boiler. This, of course, means that less heat is required from the burner to keep up the pressure of steam. The pump is at work the whole of the time the engine is running, so when the engine is requiring little steam the pump would overflow the boiler, and to obviate this a two-way cock or tap is interposed between the boiler and the pump, controlled by a handle near the driver's seat, by which he can turn the water from the pump back into the tank. A separate hand pump is fitted for filling the boiler for starting, or at any time when it requires more water when the engine is not running, but on the Locomobile a steam pump is now provided so that steam once 'up' hand pumping need not be resorted to.

We have already shown that in most cars the forcing of the petrol supply to the burner does not require a constantly acting pump, as an air-tank occasionally pumped up by hand provides enough pressure to force the petrol through the vaporiser to the burner, but in the Serpollet the paraffin (which is under air pressure) is also pumped to the burner as well as the water to the generator. The arrangement is shown at fig. 13. It has been found that six parts of water require one part of paraffin to vaporise them in the Serpollet. The oil pump o is smaller than the water pump w, and both are connected by links o¹

A 12 h.-p. Serpoilet Touring Car (date 1901)

and w¹ to the lever l, which hinges on the fulcrum d. The lever l is moved up and down by the link l¹, which is connected to the arm e. On the arm e is a roller r, which is forced up and down by eccentric discs or cams c on the shaft a, which is rotated from the engine by the toothed or cogged wheel b. The result is that, as the lever l is hinged at d, its up and down motion is greater at w¹ than at o¹, so that the water pump w always has a longer stroke than the oil pump o.

When more steam is required in the Serpollet, it simply means that more water must be forced into the heated generator coils by the water pump. At the same time the greater supply of water requires a larger supply of oil to the burner to keep the coils hot enough to evaporate it, and the stroke or up-and-down motion of the lever l can be varied by shifting the shaft

Fig. 13.—The Serpollet Water and Oil Pump

a sideways, so that cams of varying degrees of eccentricity can be brought under the roller r, and its motion increased or decreased as required. As the two pumps are both connected to the lever l, it will be seen that whether they are giving full Fig. 13a.—Example of Cams of Different Throws supply or anything below it the proportion of six parts of water to one of oil will always be maintained. On some Serpollet cars the pumps are horizontal instead of vertical, but they operate in a precisely similar manner.

Fig. 13a shows three cams in a row. These cams are eccentric discs fixed on a revolving shaft, and as the faces of Nos. 2 and 3 do not project so far from the shaft as 1, if the roller r be introduced against the face of 3, for instance, it will be moved up and down less than if it were bearing against the face of No. 1, so that all the driver has to do when he wishes to increase or decrease the steam supply to his engine is to shift a lever by the seat, which moves the shaft, on which there are eight cams (fig. 13) of varying eccentricity, when the stroke of his pump will be proportionately altered. It should be added that the roller R is kept down on to the cams by a spring, which will be noticed under the lever l (fig. 13).

Water Gauges.—All fire-tube and water-tube boilers, i.e. all boilers in which any appreciable quantity of water is carried, are fitted with a water gauge, as they are not sufficiently thick to resist damage from burning should the water level be allowed Fig. 14.—The Klinger Water Gauge to become so low that the tubes and tube plate become unduly heated. A water gauge is to all intents and purposes a glass window in the boiler. It takes the form of two taps, one below the water level, and the other above. These two taps are connected by a glass tube, provision being made to prevent leakage where the glass joins the taps. In the steam cars, as the boiler is out of sight of the driver, under the seat, tubes are provided so that the water gauge can be placed nearer to him, and a looking-glass is fitted on the dashboard, reflecting the gauge to the driver's eye.

The Klinger gauge (fig. 14) is a great improvement on the ordinary type, as it is provided with a glass window of prismatic section, and the result is that the water is shown black, and its height is much more easily read than with the ordinary glass gauge-tube. Should the driver have reason to doubt the accuracy of his gauge, he can test it by opening the tap at the bottom. All water gauges have a similar tap.

Pressure Gauges.— Pressure of steam in the boiler is expressed in this country in pounds to the square inch, and a small instrument known as a steam pressure gauge is used for the purpose. This is connected to the boiler by a pipe, and is fixed on the dashboard in front of the driver, and a hand on the dial indicates the steam pressure in the boiler (fig. 15). The interior mechanism of the gauge is extremely simple. It consists in a tube bent in a loop, as shown. One end is open to the steam pressure of the boiler, and the other end is closed, the closed end being attached to a short arm, which moves a rack engaging with a small toothed wheel

Steam pressure Gauge with face removed and Bourdon Tube in section		Steam pressure Gauge, ordinary appearance

Fig. 15.

behind the dial, and so turning the hand on its face. The gauge depends for its working on the fact that a bent tube, when subjected to internal pressure, tends to straighten itself out.

The Engine.—Having seen how the heat is supplied by the burner and steam by the boiler, we turn to the engine. This description of the engine need not be read by the novice unless he likes, as it deals with a portion of the car which is quite automatic, and which is exactly the same in its operation as the engine of that most reliable automobile the railway locomotive. Most steam cars have two cylinders, but for the sake of simplicity we will describe a single-cylinder engine, as the principle of working is identical. Fig. 16 shows the cylinder a, in which a piston b is free to move up and down. The steam is admitted alternately at the top and the bottom Fig. 16 of the cylinder by means to be described later. To the piston b a piston-rod c is fixed, and it issues through a hole in the bottom of the cylinder. Both the piston b and the hole through which the piston-rod issues from the cylinder are rendered steam-tight by means to be presently described. The piston-rod c is attached by a hinged joint d to the connecting rod e, which at the other end encircles the crank-pin f of the crank g, which moves, as shown by the arrow and dotted line, in a circle of which h is the centre. We will assume that steam is admitted to the top of the cylinder a. It blows the piston b downwards, which in its turn depresses the piston-rod c, and, as this is connected to crank c by the connecting rod e, the rotation of the crank is started. When b gets to the bottom of the cylinder, the steam supply on the top of it is stopped, and steam is admitted underneath the piston, so that it is blown upward from the underside, and the crank is pulled up. As b ascends it expels the steam from the cylinder which had driven it on its downward stroke. This action is kept up as long as the engine is at work, and by the interposition of the connecting rod and crank, the reciprocating or to-and-fro motion of the piston is transformed into rotary motion.

The Slide Valve. The admission of the steam at alternate ends of the cylinder, and its outlet after it has forced the piston down or up, is controlled by the slide valve, which is worked by the crank-shaft of the engine. Figs. 17 to 20 show the slide valve and piston in different positions, and figs. 21 and 22 give details of the steam ports, exhaust port, and slide valve. Steam ports sp, or openings, are made at the top and bottom of the cylinder, fig. 17, and these are shown in plan at fig. 21. Between them is an opening ep, the exhaust port and the slide valve sv, which from fig. 22 it will be seen

Fig. 17.—Piston at top, valve closed, just about to open

Fig. 18.—Valve open a little; piston descending

Fig. 19.—Valve full open

is a hollow box, alternately covers and uncovers the steam ports for admitting steam to the piston. While it is doing that for one end of the cylinder it is connecting the other steam port with the exhaust port, so that the steam, after it has done its work, can escape freely.

We will assume that the engine is running, and at fig. 17 the piston p in the cylinder c has reached the top of its stroke. At this moment the top steam port is closed by the edge of the slide valve, but as the piston commences to descend on its return stroke, the slide valve has also moved downward, so that the steam is admitted to the top of the piston and forces it downward, as shown in fig. 18.

In fig. 19 the piston has descended further, and the top steam port is fully open to it, but as the slide valve has also descended further, the bottom steam port is open, and the steam which had forced the piston upward in the previous stroke is now, having done its work, pushed out by the descending piston through the bottom steam port into the box portion of the slide valve, and as it will be seen that this is also open to the exhaust port, the steam passes away to the chimney.

In fig. 20 the piston has reached the bottom of its stroke, and is just commencing to ascend, steam being gradually admitted to the bottom steam port while the top steam port is

Fig. 20.—Valve open to bottom of piston; piston ascending

Fig. 21.—View of Valve face and exhaust outlet at side.

Fig. 22.—Plan View of Slide Valve

being opened by the upward movement of the slide valve, so that the steam on the top of the piston can escape into the exhaust. These actions are continued while the engine runs, and, as we have already seen how the up-and-down motion of the piston turns the crank, it is necessary for us to find out how the slide valve is moved backward and forward, so as to perform the operations we have described at the proper time with relation to the piston.

Figs 23, 24, and 25, although mainly for another purpose, will also show how the slide valve is operated. Fig. 25 shows the position of the valve when the engine is running forward. Two eccentrics are keyed to the crank-shaft. These two eccentrics f e and b e are circular discs; they are not, however, fixed to the shaft at their centres, but eccentrically. As the shaft revolves, they have an up-and-down motion, practically the same as if they were cranks. A ring encircles each eccentric, so that the eccentric itself is free to revolve in the ring. To the ring the eccentric rods f and b are fixed. At the other end the eccentric rods are connected on working joints to a curved link. In the curved link is a block b, which has a free sliding fit, and this is connected to the slide valve rod v r in figs. 17 and 22, and plainly shown in figs. 23, 24,

Diagrams for link motion

Fig. 23.—Mid Gear: no steam

Fig.—24 Backward Gear: steam at top

Fig. 25.—Forward Gear: steam at bottom

and 25. As the engine revolves the eccentric gives an up-and-down motion to the rods which are hinged to the link If we look at fig. 25 it will be seen that the forward eccentric rod is nearer to the slide valve rod than the backward eccentric, and this results in an up-and-down motion of the slide valve being produced by the forward eccentric f e, as the backward eccentric b e only forces the right-hand end of the link up and down, and does not drive the slide valve. In fig. 23 we see that by the link connected to the reverse lever by the side of the driver the curved link connecting the two eccentric rods to the slide valve has been so moved that the slide valve rod is placed in the middle of the link. As the engine revolves the eccentrics simply push each end of the link up and down alternately, giving practically no motion to the slide valve, but by moving the reversing handle so that the curved link takes position somewhere between those shown on fig. 25 and fig. 23, the travel or distance which the slide valve moves up and down is reduced, so that the steam is cut off from the piston before the end of its stroke. This process is known as 'notching up,' and it simply means that the steam, instead of being admitted to the piston almost to the end of each stroke, is cut off before the stroke is completed, the expansion of the steam being sufficient to finish the working stroke. This results in a distinct economy in steam, and is one of the first things which a driver of a steam car should learn to do, for it is often unnecessary when running fast on the level or down slight slopes to drive with the steam admitted right to the end of each stroke. This results in economising the steam, which in its turn means that less fuel is used. The backward and forward eccentrics are so set with relation to the crank that the steam is admitted and released at the proper time. When running forward, the forward eccentric does all the work of moving the slide valve up and down, and when running backward the backward eccentric performs it. In other words, the eccentric rod nearest the slide valve rod is the one which works the eccentric, and when we get into the position of 'mid gear' (fig. 23) no steam is admitted at all, as both eccentrics are working the link up and down, but not moving the valve, the block b occupying the same relation to the curved link that the boy does to a see-saw when he stands in the middle of it. The box on the side of the cylinders, in which the slide valve works, is known as the 'steam chest.' The arrows show the passage of the steam from the boiler into the cylinder and out of it, e, the exhaust outlet, being marked for clearness in fig. 23. Although we have spoken throughout as if the eccentrics were so set in relation to the crank, and the slide valve so proportioned that the steam was all pushed out by the piston when exhausting, it should be understood that the exhaust port is closed just before the piston reaches the end of each stroke, so that a small quantity of steam is what is called 'trapped' in the cylinder. This serves as a cushion, and prevents the reversal of the direction of the piston being accompanied by any shock. We do not go into the mysteries of 'lap and lead,' as they are matters which the manufacturers of steam engines satisfactorily settled long ago, and the automobilist need not trouble himself concerning them.

Anyone who is absolutely unacquainted with link motion and steam engines generally should, if he wishes to get an insight into the working of an engine, spend a quarter of an hour examining a small model steam engine. He will learn more of its working—which is very simple in itself, though laborious to plainly describe—in five minutes than he can from as many hours of reading. It should be understood, with regard to figs. 23, 24, and 25, that the link motion is shown at right angles to its true position, as, while we have an end view of the cylinders and slide valve, we have a side view of the links and eccentric rods, this distortion occurring merely for the sake of clearness. Nor are the eccentrics fixed quite at right angles to the crank, but to explain this would occupy more space than we have at our command.

The Reading Engine.—Nearly all the small steam cars are driven by two-cylinder engines, the only exception being the Reading, in which a four-cylinder engine is used. This is a most ingenious engine, which we regret space does not permit us to describe in detail. It has no slide valves, and the steam is admitted to and released from each cylinder by a single rotary valve, this one valve on the top of the four cylinders serving them all, and also providing for reversing. This engine was fully described in 'The Autocar' of April 20th, 1901, and September 21st, 1901.

Compound Engines.—The engine driving the House car is a two-cylinder one, but it is so arranged that one cylinder receives high-pressure steam from the boiler, and, instead of

 

Plan of a Locomobile Car, showing position of Boiler, Engine, Tanks, &c.

the exhaust being passed away into the chimney, it is turned into the second cylinder and drives the piston in it before being released. The high-pressure cylinder is smaller in diameter than the low-pressure cylinder, which is of such diameter that the power from the low-pressure cylinder is practically equal to that of the smaller high-pressure cylinder. For starting purposes, or when special effort is required, the driver can turn high-pressure steam into both cylinders. The idea of the compound engine is economy of the steam consumption, as more work is got out of the steam before its final release. Linking up, or using the steam expansively in an ordinary or simple engine, is done with the same end in view.

The Serpollet Engine.—This engine is designed to use superheated steam, and is entirely different from the ordinary steam engines which we have just described.

The Serpollet engine is practically an adaptation of the internal combustion engine to fit it for using superheated steam. Fig. 26 is a side view of the engine, half of it being shown in section. It has four cylinders and a two-throw crank, but only two cylinders a a are shown, as the other two are immediately behind them. It is a single-acting engine, that is to say, each piston is forced towards the crank by the steam, but it is not forced back. Instead of slide valves, mushroom valves (see chapter on Petrol Engines) are used. h shows one of these valves in section, the steam inlet valve. The exhaust valve to each cylinder is exactly the same as h, but as it is behind it cannot be shown in the drawing. The exhaust steam passes through j and out at j¹. The valve h is kept closed by a spiral spring, which encircles its stem, and h is opened and closed by the to-and-fro motion of f through g, f being moved by the cam e on the cam-shaft d, which is driven by a toothed wheel on cam-shaft c, working into a similar toothed wheel on crank-shaft d. The exhaust valve is similarly operated, and the engine is reversed by sliding another pair of cams under the rollers working the valves. A piston b drives the crank direct through the connecting rod k, exactly the same as in a petrol engine. l is the flywheel, and m a tap for letting dirty lubricating oil out of the crank chamber. Each of the four cylinders works in a precisely similar way to the one described. In some engines the valves are parallel with the cylinders instead of slightly inclined as shown in fig. 26.

Piston-rings.—These scarcely require description, as they are the same in principle as those used in petrol motors, and by turning to the chapter dealing with these the reader will be

Fig. 26.—The Serpollet Engine

able to find out how the piston, which must be a free sliding fit in the cylinder, is also pressure-tight.

Stuffing Boxes.—As the piston-rod issues from the bottom of the cylinder it is necessary that this should also be a free sliding fit, and at the same time steam-tight. These ends are attained by having a circular cavity, into which packing is inserted and held firmly by a screw ring or gland, and a locknut. Two forms of stuffing-box are shown in figs. 27 and 28. The packing usually consists of some substance in which asbestos and graphite are mainly used.

Condensers.— In damp weather, when using a full supply of steam, the exhaust from the engine shows, just as on the same sort of day the steam from horses becomes visible, and to obviate this condensers are used. For the majority of cars the Clarkson condenser is in use. This is described as a 'radiator' in the chapter dealing with internal combustion engines, and needs no further description here, except to say that, instead of water being passed through it, the exhaust steam from the engine takes its place and issues from the bottom of the condenser almost invisibly in a small stream of hot water. In the Serpollet, House, and other cars different forms of condensers are used, but the action is the same. They consist of long ranges of pipes exposed to the air, through which the steam is passed and so condensed into water. Some of the light steam

Fig. 27.—Stuffing Box with studs

Fig. 28.—Stuffing Box with screwed and flange cap

cars are fitted not only with the Clarkson condenser, but also with an oil separator and a water filter, as the steam, instead of being dropped on the road after condensation into water, is pumped back into the tank and used over again. To cleanse it from the oil, which would otherwise damage the boiler, the oil separator and the filter relieve it of all injurious impurities before it reaches the tank. By this means a car can be driven at least double as far without renewing water, that is to say, from fifty to sixty miles, instead of twenty to twenty-five. These remarks apply to cars of the Locomobile type, with the usual tanks, but by having a larger water tank and an extra petrol tank, they can be run greater distances without replenishment.

A convenient fitting is now applied to the Weston car in the form of a steam 'water-lifter.' When the tank requires replenishment, the water has to be poured in from a bucket or can, unless a hose be available, but the water-lifter does this work by steam from the boiler, and completely fills the tank in five minutes, and heats the water to 140° F. in so doing.

The Car.—We do not deal here with the car itself, nor with the transmission, as the latter has a special chapter reserved to it, and the cars, beyond their light tubular framing and generally light build and very simple transmission, are, broadly speaking, similar to the petrol carriages. It should be understood that the makes we have mentioned are cited as examples. No attempt has been made to mention numerous interesting types which do not differ in their main essentials from the cars we have described. The novice who first examines a steam car may possibly be somewhat appalled at its apparent complication, but if he examines the pipes and connections generally, and ascertains their exact mission, he will soon see that the apparently bewildering multiplicity of parts is not very formidable after all. There is no mystery whatever about the mechanism; it merely needs a short study to be easily appreciated.

As compared with a petrol car, the main advantages of a steam vehicle may be summarised in its quietness and evenness of running, ease of starting and restarting, and the great range in the power of the engine, which stops and starts with the car, and can also when necessary be used as a very powerful brake. Steam cars do not put such hard work on the tyres as those driven by petrol, as the engine power is softer in action, and nearly all of the steam cars are lighter in weight than the others. The transmission of the power from the engine to the road wheels is much simpler than it is in the case of the petrol car, but the boiler, burner, &c. make up for this simplicity. It needs more attention on the road in the way of looking after the water level and the steam pressure, but this soon becomes automatic, and is quite as unconsciously performed as the balancing a bicycle after one has once learned to ride. The cause of any stoppage can usually be more easily traced than with a petrol engine. Stops for fuel and water are more numerous, and the fuel consumption greater (about one gallon of petrol every twelve miles on average roads).

The Art of Driving.—Almost anyone can drive a steam car in a few minutes, but it requires experience to get the best results. The great art of driving is always to have sufficient steam in hand to get up any hills that may be met with on the road, and at the same time to keep down the consumption of fuel and water to

The De Dion Steam Vehicle driven by the Marquis and the Count de Chasseloup-Laubat. (See Chapter 1.)

the lowest possible limits. Considerable space might be devoted to discussing the niceties of the art of driving a steam carriage, but they may be summarised as consisting in the maintenance of an even steam pressure and mean water level on all conditions of roads, with a minimum consumption of fuel and water. If the owner takes the trouble thoroughly to understand his car and its mechanism first, and then bears this rule in mind, he will soon acquire the art, and will learn to take advantage of every variation in the gradient and road surface. Linking up plays a very important part in the economy of fuel, and by doing this whenever circumstances permit, by cutting down the fire when descending hills, and by using steam with moderation at the foot of a long hill, it is wonderful what can be done. It is also necessary to remember that the best results will be obtained by keeping the boiler fairly full. If the water is allowed to get low, a large supply has to be given to it at one time, and this results in an instant drop of steam pressure. The great thing for the novice to guard against is 'burning the boiler' by allowing it to become nearly empty, so that it gets overheated. Care should also be taken that the engine and all working parts are properly oiled—never allowed to run dry or to be flooded with needless oil. The boiler should be 'blown down' twice a week when the car is in use. When the drive is finished the pressure should be allowed to fall to 50 pounds, and then the blow-off cock or tap opened so that all the water is blown out, and with it all sediment and deposit which would otherwise form a coating on the inner surface of the boiler and tubes. This is like the 'fur' in a kettle, and not only reduces the steaming power of the boiler, but also eats away the metal. So long as the boiler is regularly 'blown down' it will not get furred.

Quite apart from questions of economy, the owner who studies his car and endeavours to get the best results out of it will find that his interest in the pastime is greatly increased, as he is provided with an interesting occupation the whole time he is driving, and never for one minute does the way seem long or the driver feel bored. Finally, the driver should always make a point of seeing that everything is in good order, as it should be before he starts out, and he should not leave trifling but necessary adjustments, which might have been seen to before he started, to be performed on the roadside. If he follows this advice he will have a vehicle which is as trustworthy as a railway locomotive, and almost as durable.