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Presented at
Cleveland Section Meeting
October 20, 1916

STEAM MOTOR-VEHICLES

BY ABNER DOBLE*
* Vice-president, General Engineering Co.

(Detroit Section Associate)

 

The purpose of this paper is to present a summary of investigations covering a period of nine years. These were made to determine the possibility of overcoming certain serious objections and disadvantages under which the steam motor-vehicle formerly labored.

Ten years ago steam cars were in their zenith—not that a large number of makers were producing them, nor yet that the majority of cars were steamers, but rather that a most progressive and prosperous organization was producing these cars on a real quantity basis. The White steamer of that day was universally respected or beloved, accordingly as the person affected was a gas-car man or a steamer advocate.

The Stanley steam car has been manufactured since 1898 without cessation. The evolution of this car has been gradual and conservative, and it has enjoyed a well-merited reputation for service at low cost. A fire-tube boiler and locomotive-type engine have been used from the first. Stanley Bros. have added improvements only when there was a well recognized demand. They have thus accumulated those necessities of modern motor cars, such as electric lights, streamline bodies and one-man top. A condenser was adapted to the car in 1914, and as a result about 200 miles can be covered on one filling of the boiler. Kerosene is now burnt in the main burner (with gasoline for starting and for the pilot), and the mileage per gallon is high. The fusible plug has been abandoned in favor of a thermostat for shutting off the fuel in case the supply of water runs short.

A large number of more or less ineffective attempts have been made to produce a satisfactory steam-car by persons ill-informed on the actual requirements and apparently lacking in the necessary understanding of automobile-production conditions.

Immediately after the early-day popularity of the steam-car the internal-combustion engine began to be favored by engineers. With the introduction of the long-stroke high-speed engine in Europe the steam-car fell behind rapidly in the march of progress. I do not wish to convey the impression that motor-vehicle builders erred in selecting the gasoline engine. The market demanded cars and more cars, and the makers chose the only practical powerplant available. No one wanted a vehicle that emptied a horse-trough every twenty miles. Very few drivers were equal to the task of properly feeding the boiler. The idea of spending all the way from a quarter of an hour to an hour and a half in starting soon lost its relish.

LOW MILEAGE A DISADVANTAGE

One great disadvantage of the steam-car was the insufficient mileage that was obtained from the water that could be conveniently carried. Several steam-cars were equipped with an apparatus intended to condense the steam, but a continuous run of 100 miles without refilling was uncommon. Owing to the use of heavy cylinder-oil these condensers as well as the water tank required periodical cleaning. Steam cars not so equipped would run approximately 30 to 35 miles on a tank-full, about 35 to 40 gals.

Apparently no one had considered using a honeycomb radiator. The reasons advanced against it were that the thick oil was liable to clog the extremely small passages, and that the exhaust steam (particularly in cars with flash boilers) was liable to melt the solder. It was also believed that oil would injure the boiler, cause violent foaming and that the successful lubrication of a steam engine required a heavy molasses-like oil. It was particularly hard to reconcile these beliefs, and we determined that the best thing to do was to put a honeycomb radiator on a car and operate it with a fire-tube boiler. This we succeeded in doing late in 1913, and obtained several startling results. The car would run anywhere from 1000 to 1500 miles on one tank (24 gal.) of water. The boiler operation was entirely unaffected by the oil pumped into it from the engine cylinder. Having shown that it was possible to travel an adequate distance on one supply of water, we turned to the study of the steam-generator, with special regard to its operation when fed with water containing oil, graphite, and in winter, alcohol.

The so-called flash boiler, consisting of a series of coils forming, in effect, one continuous tube, was naturally out of the question. Its entire absence of steaming stability was a source of constant aggravation to a driver in a hilly country. However, it had the immense advantage that the direction of the water-flow was opposite to the flow of the gases of combustion, which allowed the water to take the last possible heat unit from the flue gases. Its all-steel construction with consequent immunity from leaks due to low water was also a great advantage.

The vertical fire-tube boiler was also out of the question for production on account of its great weight, potential danger present with a large diameter shell, its high cost because of the apparent necessity of winding the shell with a mile of piano wire and its liability to leaks both from oil working through the expanded joints where the tubes were fastened into the heads and from overheating with low water. Notwithstanding these formidable disadvantages, when in good condition it was the best boiler from the driver's standpoint, owing to its large reserve of water heated to the steam temperature, which admitted of great acceleration. It was also efficient because of the surface-heating arrangement with extremely short distance through which the gases radiated heat to the tubes.

The water-tube boiler, which has been built in almost every conceivable shape for motor-vehicle service, seemed to offer a basis on which the good characteristics of the flash and water-level types of boilers might be combined. This at first seemed a forlorn hope, as the apparently conflicting conditions seemed unreconcilable.

Deposits of scale occur in every type of boiler, with a resultant drop in efficiency and added liability of burning the already extremely hot heating-surface. In the water-level types this scale would settle in the non-circulating portions of the boiler, such as the water-column and blow-off connections.

STEAM-GENERATOR REQUIREMENTS

In studying these apparent conflicts, we could see that all functions were closely related. That is, a water-level boiler held the temperature of the steam practically constant, with no possibility of temperatures high enough to effect a deleterious change in the lubricating oil. This allowed the same oil to be used over and over. It also allowed the use of a soldered radiator to condense the exhaust steam. The honeycomb radiator condenses such a large portion of the exhaust steam, that little make-up water is required, with the result that much less scale is introduced into the system. Since little water is lost, in winter, alcohol can readily be used in large enough proportions to prevent freezing. The use of a mixture of alcohol and water results in an imperceptible drop in power because of the large amount of heat-carrying medium that must be circulated.

The use of regular gasoline-engine cylinder-oil for the lubrication of those parts in contact with the steam, would make a steam generating and condensing system of this kind practical. Such oil is more agreeable to handle and easier to procure than the heavy oil used in steam engines. It rapidly forms an emulsion with the water, owing to the violent agitation and intimate contact. It cannot form clots and clog up the radiator passages, and since the return from the radiator is introduced into the bottom of the water-tank the agitation of the contents of the tank is sufficient to maintain the emulsion. This insures that the oil is regularly pumped into the boiler along with the water. The oil that thus finds its way into the boiler performs several valuable functions: First, it coats thoroughly every portion of the interior of the boiler with an exceedingly thin film of oil. While this is thin at ordinary temperatures, it is much thinner at 485 deg. F., which is the approximate temperature of the boiler at 600 lb. pressure.

Scale will not stick to a surface coated with oil, so that the interior of the boiler is absolutely protected from scale as well as from rust. Very little scale-bearing water is introduced into the system because of the efficient condenser, but in several years' operation enough scale would be formed to render a boiler useless, even though none of it adhered to the tubes. The second function of the oil in the water is to combat this condition, which it does with thoroughness and dispatch. As soon as a particle of scale is thrown out of solution it is thoroughly coated with oil, which renders it incapable of sticking to any other particle. This scale therefore remains in suspension, and owing to the violent ebullition and constant flow toward the steam outlet is carried along and out with the steam, finally reaching the water-tank. This action appears to be exceedingly thorough, and in several years' use no accumulation of scale can be detected in any portion of the boiler. It appears that the scale problem can be solved when such particles of foreign matter are kept small enough so that they will be readily carried over with the steam.

The steam generator, Fig 1, which has been worked out to fulfill these interrelated conditions, is a flash-generator in theory, yet has the appearance of a water-tube boiler and has a water-level in the evaporating zone. The close and regular heating-surfaces give heat-transfer conditions resembling those of a fire-tube boiler, and yet the progressive water-flow, counter to the flow of the gases, with no circulatory flow, is characteristic of the flash type. The water enters the bottom of an economizer-zone and flows to the top under the action of the pumps and gravity; the hottest water collects at the top. From there the water overflows through a connecting pipe into an evaporating zone, where it is converted into steam. The water-level is maintained about half-way up the generator by an automatic by-pass valve; this is so arranged that when the regulator tube is filled with steam the by-pass valve is closed by the expansion of the tube, forcing the water from the pumps to lift the check-valve. The water can then enter the generator. As the water-level rises, the regulator tube is filled with water from an exposed pipe leading from the water manifold. This water is not in circulation in the generator, and therefore remains quite cool. The regulator tube then contracts and opens the by-pass valve, allowing the water to return to the tank.

The generator tubes are vertical, swaged at the ends to half their diameter, and welded into horizontal headers, top and bottom. Each section thus formed is connected to manifolds, top and bottom, for the exit of steam and the entrance of water. This construction is absolutely without danger of explosion and is also cheap to manufacture. Any damaged section can be replaced, or isolated pending replacement, in a few minutes. The casing of this generator consists of a ½-in. asbestos board, ¼-in. of mineral wool and a planished-iron jacket.

STARTING STEAM CARS

Perhaps the greatest disadvantage in operating steam-cars was that known as "firing-up," or getting the burner started to raise steam. Steam-cars almost without exception have used a Bunsen burner of the vaporizing type, which required pre-heating to vaporize the fuel. This was necessary to insure that enough mixture passed into the combustion space to ignite readily and to continue burning. After combustion was well under way the fire kept the vaporizer heated. When standing, a supplementary burner was lighted to maintain the vaporizer heat; this ignited the main burner when the car was to be used again.

About three years ago we first tried to eliminate the time and labor required to start combustion. It was suggested that a carbureter and spark-plug be used—a blower driven by an electric motor to furnish the requisite air, the idea being to use these with a regular Bunsen burner. This was found to work fairly well with gasoline, except that undesirable precipitation of the fuel took place. It also seemed necessary to provide means by which kerosene could be used for starting, without recourse to gasoline.

We finally discovered that kerosene could be ignited by an electric-spark with absolute certainty and regularity, if these conditions are observed: First, the kerosene must be separated mechanically, so that the individual particles are sufficiently small to insure a rise in temperature past the point of ignition during the time in which they absorb heat from the spark; second, the spark must occur near the atomizing nozzle, at which point the fog is so dense that one group of kerosene particles igniting, invariably ignite the rest. Third, the velocity must be so low that the particles can absorb sufficient heat from the spark to exceed the ignition temperature. Fourth, the mixture must be much richer at the point where ignition is to occur than is that for most efficient combustion. The combustion should occur in a refractory chamber so arranged that it attains an extremely high temperature; complete combustion of a large amount of fuel can then be obtained in a small space.

Thus, in a complete apparatus we have an electric motor, direct-connected to a multivane blower, and a graduated kerosene pump. The kerosene pump draws a measured quantity of fuel from the supply tank and forces it through the atomizing nozzle; the resultant fog is ignited by a spark-plug. A measured amount of air is forced in by the multivane blower, which whirls the rich ignited mixture down through an inlet tube against the bottom of the refractory combustion chamber, where the fuel is consumed. To stop the combustion it is only necessary to break the blower-motor circuit. This is done automatically by a regulator set to operate at a pre-determined steam pressure.

With the old-fashioned Bunsen burner, which has been used on all previous steam-cars, it is necessary first to heat the vaporizer. This is done with a drip-cup or a painter's blow torch, although on modern steam-cars acetylene gas is used. The fuel valve is then opened slightly, allowing very little fuel to flow until the burner has become well heated, after which the fuel valve can be left open. The starting of the fire takes about six minutes and requires the care of the operator until it is going well. After the fire is started, steam is made quickly. On some types of boilers enough pressure can be raised to start the car in about a minute and a half after the fire is under way. It is therefore apparent that if practically the entire time formerly used in starting the fire can be saved, it is a reasonably simple matter to build a powerplant that can be started in a short time, with no labor or attention required.

The engine of a steam vehicle should last for many years of hard service. It has proved to be a relatively simple matter to provide ample dimensions of the working parts so that the mechanism is safe for continued operation under maximum conditions of load. In order to have efficient working it is necessary to provide for high expansion. This can be obtained with a compound engine, but not satisfactorily, as the ratio of cylinder volumes has to be carefully determined in relation to the probable loads, speeds and steam-chest pressures. These conditions vary so widely that the single expansion engine, Fig. 2, is necessary.

To provide the high expansion desirable, with a simple noiseless valve gear and one valve per cylinder, it is imperative to use the uniflow principle. In the uniflow engine the valve takes care of the steam inlet only, the exhaust passing out through ports at the end of the stroke when these are uncovered by the piston. It is thus possible to secure cut-off at 5 per cent of the stroke. Since the thermal conditions in the uniflow cylinder are practically ideal, it is unnecessary to use superheated steam. This means that little cylinder lubrication is required, and the troubles formerly caused by superheated steam are absent.

The engine directly geared to the axle, with a 47 to 48 ratio, can produce enough torque to slip the driving wheels on dry ground. The slow engine speed thus possible makes elaborate lubrication systems superfluous. The general arrangement of the principal parts of a steam-car is shown in Fig. 3.

ADVANTAGES OF A PERFECTED STEAM POWERPLANT

1. Torque range of 100 per cent with a maximum torque available at zero speed; change-gear mechanisms and clutch therefore unnecessary. Mean effective pressure (and equivalent drawbar pull) always under control of the operator; variable by throttle from zero to maximum, a maximum limited only by the resistance between the driving wheels and road.

2. Utmost mechanical simplicity, with not over twenty-five moving parts in the entire car, and only fifteen in the engine.

3. Smooth and quiet operation, owing to low engine speed and to location of engine on axle.

4. Low running cost; kerosene or crude oil used for fuel.

5. Low manufacturing cost owing to simplicity of construction and lack of fussy work in production.

6. Entire absence of lubrication troubles; no contamination of crankcase oil by kerosene, gasoline, water, road-dust and carbon.

 

 

DISCUSSION

E. G. THOMAS:—This paper recalls a conversation with Mr. Doble, in which he contended that multicylinder engines are unnecessary when if steam is used a two-cylinder engine is sufficient. We then rode in his car at speeds varying from 1 to 60 m.p.h. It was a most pleasing sensation. There was absolutely no noise. The car attained any speed desired at any time.

MR. UTICH :—What does the seven-passenger car weigh?

ABNER DOBLE:—A seven-passenger car of 128-in. wheelbase, 56-in. tread front, 57-in. tread rear, equipped with a rather heavy body and 33 by 5-in. wheels weighs 3100 lb., with tank filled ready for the road.

CHAIRMAN ARTHUR J. SCAIFE:—What is the greatest horsepower obtainable with this type of powerplant?

ABNER DOBLE:—The highest normal horsepower that we have used so far is 25, but a 25 hp. steam powerplant at the standard pressure of 600 lb. per sq. in. will exert about 132 hp. for about eight minutes.

S. L. BLACKBURN:—What is the maximum pressure capacity of the boiler?

ABNER DOBLE:—The boiler is designed for a working pressure of 600 lb. The safety valve is set for 1000 lb. The boilers are all tested to 5000 lb. They will rupture at about 8500 to 9000 lb. At this pressure the tubing ruptures at a place remote from the welds. My own car has been in service since December, 1913. The safety valve has never blown. This means that the maximum pressure has never reached 1000 lb.

THERMAL EFFICIENCY

WALTER C. BAKER:—Why is an efficiency twice that of a gasoline car claimed?

ABNER DOBLE:—Everything depends upon what you mean by "efficiency." We know that 18 per cent thermal efficiency is obtainable from a gasoline engine running at full load. We also know that cars do not run at full rated load much more than 1 per cent of the time. .When running at 20 or 25 m.p.h. about 5 hp. is required to drive the car. Under such light load the ordinary engine will have a thermal efficiency of about 4.5 to 5.0 per cent. The highest thermal efficiency we know of to-day with the steam powerplant is about 21.8 per cent at its full rated load. This is obtained by using a combustion system in which the air is preheated, at the risk of burning out the grate bars. The Doble steam generator has no grate bars, but uses a refractory material that we developed. It will stand about 3400 deg. F. before it fuses. The temperature attained in our fire box is about 2600 deg. F. The air is preheated to 200 deg. before it enters the carbureter, by utilizing about one-third the heat that would otherwise go out of the stack. The boiler efficiency without the economizer is about 82 per cent. This is equivalent to standard practice in boilers. With our boiler we can increase the efficiency about 4 per cent by the economizer and by using a regenerator, which can be placed on the end of the stack, we can raise the boiler efficiency to about 92 per cent. The best net thermal efficiency that we have been able to secure from our powerplant is about 16 per cent under full load. With the 5 hp. load imposed when a car is driven at 25 m.p.h., we realize 14 per cent net thermal efficiency. My car, which was built three years ago, and is crude in some ways, has been driven almost 40,000 miles. It will run 15 miles to the gallon of kerosene under favorable conditions, and will average about 11.5 miles per gallon, although I drive through traffic and mud a part of the time. The old type of steam car never ran more than 7 miles per gallon.

H. H. NEWSOM :—What piston speed is used in the engine?

ABNER DOBLE:—We have found that the most efficient piston speed is 375 ft. per min., which corresponds to a car speed of about 37 m.p.h. 1 have driven my car 80 m.p.h. The corresponding piston speed is 800 ft. per min., not counting the slip, which would be about 12 per cent at that point, making a maximum piston speed of about 900 ft. per min. I have never run an engine at any higher speed than that in a car.

H. H. NEWSOM :—What is the temperature of the steam?

ABNER DOBLE:—The theoretical temperature of saturated steam corresponding to a pressure of 600 lb. is 490 deg. F., but we find sometimes that on ordinary loads, there will be 100 deg. superheat in excess of that. Under full loads it will be down to 490 deg. F., owing to the fact that we will then probably have 3 to 5 per cent of moisture in the steam.

TYPE OF COMBUSTION SYSTEM

MR. WAITE:—What sort of a combustion system is used?

ABNER DOBLE:—An efficient blower furnishes the requisite amount of air, and mixes with it enough kerosene to make a very rich vapor. The kerosene is atomized and the vapor ignited by an electric spark before the air required for complete combustion is added. The spark-plug is connected in parallel with the blower-motor circuit. The ignited mixture flows through the inlet tube and into the combustion chamber, where it burns completely before the hot products of combustion pass through the boiler.

MR. SCHWARTZENBERG:—What about the fire hazard?

ABNER DOBLE:—It is negligible with kerosene as fuel.

WALTER C. BAKER:—Is the exhaust clean when using kerosene?

ABNER DOBLE:—Yes. All carbon is. consumed at 1800 deg. F. The combustionchamber temperature under normal working conditions is about 2450 deg. The feed is set so that the fuel is entirely consumed. The exhaust will smoke sometimes in starting, until a temperature of 1800 deg. F. is reached in the combustion chamber.

MR. SCHWARTZENBERG:—Is the heat objectionable when driving in summer weather?

ABNER DOBLE:—The generator is insulated with a special material that does not reach a temperature of much over 150 deg. F. We use a dashboard that comes down to the frame, and then the frame is covered with a floor. A space of 2 in. is allowed between that floor and the floor-boards proper. We use a 1-in. cocoa mat on top of the floor-boards. The result is a much cooler car than one of the regular gasoline type.

CHAIRMAN ARTHUR J. SCAIFE:—How flexible is the powerplant? If the throttle is opened or closed suddenly, what is the variation in pressure?

ABNER DOBLE:—If the throttle valve is suddenly opened wide with the car at a standstill, the pressure will drop from 600 to 450 lb. by the time the car reaches a speed of 60 m.p.h.

WALTER C. BAKER:—How many seconds does it take to start?

ABNER DOBLE:—Five and one-half seconds from a standstill to 30 m.p.h.

E. L. CLARK:—Fig. 3 shows the engine built right onto the back axle. What is the unsprung . weight?

ABNER DOBLE:—The unsprung weight added to the axle on the older car was 100 lb. The new engine will add about 10 lb. more, but we have saved about 15 lb. in the differential, as we use no differential cage. The piston, piston-rod and cross-head weigh about 8 lb. on each side of the engine. The latter runs at 600 r.p.m. when the car is traveling 60 m.p.h.

Over 200 steam-driven omnibuses have been running for a long time in England. Last year they changed the fuel from kerosene to coke. The latter is fed by automatic stokers driven from the engine. The grate rocks so many times a mile, and all the driver has to do is shove in a little more coke every 10 miles or so. Coke sufficient for about 50 miles is carried. They also use coke-burning steam lorries.

A. M. DEAN:—What is the temperature of the engine when running at 25 or 30 m.p.h.?

A13NER DOBLE:—The steam temperature at the intake when running at 25 m.p.h. is just about 390 deg. F. The temperature at the exhaust, in every case, is 212 deg. F., or within 2 or 3 deg. of that, because at the exhaust the steam contains about 15 per cent water.

S. L. BLACKBURN:—What is the piston displacement of the engine?

ABNER DOBLE:—It is 314 cu. in. per revolution.

MR. DUNKIN:—What is the bore and stroke of the engine?

ABNER DOBLE:—It has a 5-in. bore and 4-in. stroke.

REVERSING ENGINE

E. L. CLARK:—How is the engine reversed?

ABNER DOBLE:—The "Joy" valve gear used was invented a long time ago by David Joy in England. It is the same gear that the White company used on its engines. The engine is reversed simply by changing the timing of the valve; that is accomplished by tipping the rock shaft to an inclination opposite to that used in running forward.

H. H. NEWSOM:—Does the Joy valve gear have a link motion?

ABNER DOBLE:—No, it does not. It is called a radial valve-gear, and is driven from the connecting-rod, as shown in Fig. 2. The end of the anchor link is nearly horizontal. The valve link is attached to what we call the "correcting" link, because without it the valve would not have a correct motion.

H. H. NEWSOM:—Is the control manually operated?

ABNER DOBLE:—The control is by a pedal.

H. H. NEWSOM:—Is it advanced as the speed increases?

ABNER DOBLE:—No; to start the car the pedal is moved to the first notch. That gives cut-off at three-quarter stroke. At higher speed, fuel can be saved by moving the pedal to the next notch.

W. D. APPEL:—What is the maximum cut-off when the valve gear is in the extreme position?

ABNER DOBLE:—The maximum cut-off is 21/2 in. on a 4-in. stroke. There are two other positions; the first for ordinary running and for extreme acceleration is one-quarter stroke, and the second for economical running, or for extremely high speed after acceleration has cut-off at one-eighth stroke.

W. D. APPEL:—With the cut-off set at one-eighth stroke, would it be possible for the engine to stop an dead center so that it could not be readily started?

ABNER DOBLE:—Unless the cut-off is later than mid-stroke, this can occur. In order to start under this condition, it is necessary to use the reverse pedal first.

PRODUCTION COSTS

MR. SCHWARTZENBERG:—With a properly equipped plant, turning out three hundred cars a day, and with metal at normal prices, what would be the cost of manufacture as compared to a $2,000 gas car?

ABNER DOBLE:—A car to give the same power performance as a Cadillac, for example, and with the same finish and quality of workmanship, will cost $198 less per car. In general, the saving will amount to 8 or 10 per cent of the list price of the car.

S. L. BLACKBURN:—Can the car be built in any class? Say for example in the $700 class?

ABNER DOBLE:—Yes. But the performance will be better and less care is necessary in finishing and fitting pistons and cylinders.

C. E. WILSON:—Are the braking possibilities the same as in gasoline cars?

ABNER DOBLE:—Yes; by using the reverse pedal, it is possible to stop almost instantly. Beside this, two sets of brakes are provided as required by law. The center of gravity of the car is low and nearer the rear than in gasoline cars, hence the car holds the road better and the wheels do not slide so much 'as they would otherwise. This makes the braking action more effective.

CHAIRMAN ARTHUR J. SCAIFE:—How is the engine lubricated?

ABNER DOBLE:—By the time the steam enters the cylinders, it contains about 3 per cent moisture, which increases to about 8 per cent as the expansion takes place. This moisture does the lubricating. Little internal lubrication is required, for the piston speed is low at ordinary driving speeds. The cylinder surface is cast iron, which is easy to lubricate. We use oil to prevent corrosion and to help lubrication. The last gallon of oil I used in my car was sufficient for 12,200 miles operation. The oil used is primarily to clean the scale from the boiler.

GEORGE W. SMITH:—What is the weight of the powerplant?

ABNER DOBLE:—The new engine will weigh about 240 lb. The old engine weighed 220 lb. The generator will weigh about 520 lb.; the water tank about 250 lb. The radiator will weigh 15 lb. more than a gasoline-car radiator. The engine will develop 70 hp. continuously.

H. H. NEWSOM :—Locomotives have traveled 50,000 miles without any oil in the cylinder. Cast iron will get along with little or no lubrication.

E. L. CLARK:—Is there any possibility of knocking off the cylinder head because of water in the cylinder when starting?

ABNER DOBLE:—We use ordinary slide valves, placed under the cylinders. Water that condenses in the cylinder drains into the steam chest, because the valves fall away from their seats. The car can stand for days and the throttle then be opened suddenly without injuring the engine.

E. H. SHERBONDY:—How is the water from the condenser handled? Do you carry it back to the main supply tank and then into the boiler?

ABNER DOBLE:—The water from the condenser goes through a pipe into the bottom of the water tank. From there it is forced into the boiler by the boiler feed pump.


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