Burlington, New Jersey
We thought you folks would be interested in this experimental locomotive and for that reason we give it a prominent place and much detail. Editor
Locomotive 60,000, the subject of the present publication, was designed and built by the Baldwin Locomotive Works as an experiment to ascertain the gain in efficiency by the use of high pressure steam and high ratios of expansion. Opportunity was also taken to try out certain novel details of construction.
Through the courtesy of the Pennsylvania Railroad the locomotive was submitted to an extensive program of tests on their locomotive test plant at Altoona (Pa.), and it was subsequently given road tests on this line and on a number of other prominent railroads.
DESIGN AND CONSTRUCTION
The locomotive forming the subject of this bulletin is the 60,000th locomotive built by The Baldwin Locomotive Works. It was built during the early part of the year 1926 as an experiment to ascertain the possible economies which can be effected by the use of high steam pressures and a high ratio of expansion.
Up to a certain period, development of locomotive design brought with it mainly an increase in, weight of individual locomotives, the increase in power being proportionate to the increase in weight. This increase in power made possible notable economies in railroading. Of late years, however, the demand for still further economies has led locomotive) designers to strive to increase the efficiency of the locomotive, and thus give increased power per unit of locomotive weight. Among the means adopted successfully to this end, are the use of superheated steam, various fuel and labor-saving devices, improved boiler design, more efficient steam distribution, and refinements in design and materials for locomotive parts.
At present much thought is being given to the possibility of using higher steam pressures and higher ratios of expansion to give greater cylinder efficiency and consequently greater horse-power per unit of weight.
The great advantage of high pressure steam is that a combination of adequate cylinder force and a high ratio of expansion can be obtained with cylinder of moderate dimensions.
High-pressure (1), inside
27' x 32'
in working order
Low-pressure (2), outside
27' x 32'
On driving wheels
Piston, 14' dia.
12' x 13'
' truck, front
11' x 13'
' ' and tender
ENGINE TRUCK WHEELS
7' x 12'
9' x 14'
745 sq. ft.
1645 sq. ft.
2775 sq. ft.
Length of grate
27 sq. ft.
12,000 U. S. gal.
5192 sq. ft.
1357 sq. ft.
82.5 sq. ft.
Total engine and tender
The figures here given are based on the outside diameters of the boiler tubes and flues, and the inside diameter of the super heater tubes. The figures given on page 50, which were used in computing the results of the tests, are based on the inside diameters of the boiler tubes and flues, and the outside diameter of the superheating tubes.
In view of the limits set to steam temperatures by the method of producing the steam and by difficulties of lubrication, locomotive designers must, at least for the present, aim at a steam temperature of approximately 650 degrees F., with a maximum of say 700 degrees, irrespective of the pressure used. Now, if the pressure is increased while the temperature remains constant, the superheat and the heat content per pound of steam fall off as the pressure is increased. For example, a steam temperature of 650 degrees F. gives, at 200 pounds per square inch, about 263 degrees superheat and 1340 B.T.U. per pound of steam, and at 350 pounds per square inch about 217 degrees superheat and 1332 B.T.U.
If steam of 200 pounds per square inch and of 350 pounds per square inch is expanded from the same temperature under such conditions in each case respectively that the exhaust steam escapes at the same pressure and temperature, and with the same heat content in both cases, it follows that the heat taken from the steam in the cylinders and converted into mechanical work will be slightly less with the high than with the low pressure steam. That is, with the same heat content in the exhaust steam, the higher pressure will not give greater thermal efficiency. To reduce the heat content of the exhaust steam and thus increase the thermal efficiency, it is necessary to increase the ratio of expansion.
An increase in the ratio of expansion results in a reduction in the mean effective pressure obtained from a given boiler pressure, and this requires an increase in cylinder dimensions if the same power is to be developed. Now in a large modern locomotive of conventional design, an increase in cylinder dimensions to permit of higher expansion would lead to difficulties in design, and it is advantageous to use a higher boiler pressure so that the increase in expansion can be obtained without involving a loss in power or an abnormal increase in cylinder dimensions.
As a means of obtaining the higher expansion necessary to give economy with steam of 350 pounds per square inch, Locomotive 60,000 was designed with three cylinders compounded, the high-pressure steam being first admitted to the middle cylinder. After expansion there, the steam passes through the receiver in the cylinder saddle to the two outside cylinders where further expansion takes place.
Steam pressure of 200 to 215 pounds per square inch have been currently used for a number of years, and in the last two or three years a considerable number of locomotives have been built for working steam pressures of 240 and 250 pounds per square inch. This latter is probably about the maximum pressure which can be carried successfully in boilers of conventional design with fireboxes having flat sides braced by staybolts. The stayed firebox is the weakest point in a locomotive as ordinarily designed, and with pressures carried above 250 pounds per square inch a change in design is necessary to eliminate excessive trouble with staybolt breakage. The decision to use a pressure of 350 pounds per square inch in Locomotive 60,000 led to the adoption of a water tube firebox, and the elimination of all staybolts.
The locomotive is of the 4-10-2 type, built for freight service, with driving wheels 63 inches in diameter, and three cylinders each 27 inches in diameter by 32 inch stroke. The total weight in working order is 457,500 pounds, of which 338,400 are on driving wheels. Full detailed dimensions are given on page 6. (Ed. note. The dimensions are found under one of the accompanying pictures).
Apart from the modifications necessary to the use of the water tube firebox and the high pressure, the boiler does not differ in principle from that of the conventional locomotive. The boiler barrel is of the usual fire tube type having 206 2-inch tubes and a type A super heater carried 50 5-inch flues.
The barrel consists of three courses, having plates respectively 1 and five-sixteenths, 1 and three-eighths and 1 inches thick. The third course is sloped on top, increasing the shell diameter from 84 inches at the front end to 94 inches at the back. All circumferential seams are double riveted, and the longitudinal seams are of the so-called 'saw-tooth.' octuple riveted design, which provides a short caulking distance between rivets. At the rear, the barrel is closed by a tube sheet, which is riveted to the shell in the same manner as the front tube sheet. The boiler tubes and flues are welded into the rear tube sheet.
None of the studs tapped into the boiler passes all the way through the sheets, hence there can be no leaky studs or stays.
The firebox is of the water-tube type, each side wall consisting of 48 tubes 4 inches in diameter connecting a hollow cast steel mud-ring at the bottom to one of the horizontal cylindrical drums at the top. Outside of these side tubes a firebrick shell is built, over which are applied removable cover plates which are covered with magnesia sectional lagging and jacketed. The front and back walls of the firebox are of firebrick, and the opening between the two drums forming the crown of the firebox is also closed with firebrick.
This construction provides a boiler entirely free from staybolts and from flat surfaces requiring staybolts. This feature of the design gives it an important advantage when high steam pressures are to be carried.
The depth of the firebox from the top of the mud-ring to the center line of the drums is 6 feet 6 inches. The total volume, including combustion chamber, reaches the large figure of 683 cubic feet. This gives 8.3 cubic feet of volume for each of the 82.5 square feet of grate area, which is a high relative volume for a modern locomotive, and aids in securing effective and efficient combustion.
The two drums are each 26 inches in diameter, and the transverse distance between their centers is 31 inches. They have a total length of 23 feet 6 inches, and extend into the boiler barrel a distance of 5 feet 6 inches ahead of the back tube sheet. The openings in this sheet, through which the drums pass, have flanges 65/8 inches in depth, to which the drums are double riveted. Each drum is closed, at the rear, by a cover plate which is secured to an internal ring by means of studs, and is fitted with a copper gasket to keep the joint tight. By removing these covers the drums can be entered for purposes of inspection, and the water tubes can be 'turbined' during washing-out, to remove any scale. This can be done without removing any of the lower plugs, one of which is placed in the mud-ring opposite each tube end for rolling the tubes.
Evidence obtained in road tests with different kinds of water shows very light accumulation of scale in the drums and water-tubes. This indicates that less frequent turbining and cleaning are necessary than with conventional type of stayed firebox.
The third course in the boiler barrel is sloped on top, and the two upper drums are so located that their forward extensions come in contact with this course and are riveted to it. This acts as a support for the drums, and tend to counteract the cantilever effect of the long overhanging firebox. Furthermore, to balance the effect of the pressure on the covers at the back ends of the drums, three longitudinal stay rods are run from the forward end of each drum to the front tube sheet. These rods are anchored to internal braces which are riveted to the drum. This construction, together with a system of braces connecting the front end of the mud-ring and the boiler barrel, relieves the back tube sheet of any tendency to distortion, due to the firebox overhang and the pressure on the drums heads.
The hollow cast steel mud-ring is connected to each upper drum by 48 tubes each 4 inches in diameter; and there are also four tubes connecting the drums to the back section of the mud-ring. All these tubes are swedged to a diameter of 3 inches at the mud-ring end, where they are rolled and belled, while at the drum end they are rolled, belled and welded. The tube holes in the mud-ring have two depressions rolled into them, into which the tubes lock themselves firmly when being rolled in. Water connection between the bottom of the boiler barrel and the front end of the mud-ring is made by two elbow pipes, each 9 inches in diameter, and placed right and left.
The mud-ring, which has a total length of 18 feet 2 inches and a width of 8 feet 5 inches, is cored throughout to permit water circulation. The rectangular outer frame is crossed by a central longitudinal member and also a transverse member located about six feet back of the front end of the firebox. From this transverse member, which lies at the front end of the grate, five water tubes extend to the upper drums, and serve as supports for the brick arch. That portion of the firebox which is forward of the arch constitutes a combustion chamber and is closed, at the bottom, by a horizontal steel plate, and floored with firebrick. A Y-shaped cinder pocket is applied for cleaning this combustion chamber.
The locomotive is at present arranged for burning coal, and is equipped with a Duplex stoker. It has, however, also been operated as an oil burner.
The dome is placed on the second barrel course, and is connected with the super heater header by an internal dry-pipe. A smoke box throttle of the multiple type is applied, and there is a shut-off valve for the steam supply in the dome.
The three cylinders, with their steam passages and steam chests, are formed in a single grey iron casting. The high-pressure steam chest is placed in the saddle, on the right-hand side, and is connected with the super heater by a single steam pipe. All the piston valves are 14 inches in diameter, that for the high-pressure cylinder being arranged for inside admission, while the valves for the low-pressure (outside) cylinders are arranged for outside admission. The high-pressure exhaust is conveyed to the low-pressure steam chests through passages cored in the cylinder casting; while the exhaust from the low-pressure cylinders passes to the smoke box through outside pipes which terminate in a single exhaust nozzle. A Worthington feed-water heater is applied to this locomotive, and a branch from each exhaust pipe conveys the steam to the heater.
For starting purposes, live steam is admitted to the low-pressure cylinders through a 1-inch pipe leading from a manually-controlled valve in the cab. This creates a back pressure or. the high-pressure piston, relieving the same from the full effect of 350 pounds' pressure.
The two outside cranks are placed 90 degrees apart, so that there are four even exhausts per revolution, and the inside crank is placed at 135 degrees from each outside crank. The high-pressure piston is connected to the second pair of driving wheels, and the two low-pressure pistons to the third pair. All three piston heads are of the built-up type, with spiders of open hearth cast steel. The main and side rods are of carbon vanadium steel, while the driving axles, main crank pins and piston rods are of open hearth steel, heat treated, oil quenched and hollow bored. The crossheads are of the underhung multiple bearing type, as developed by Mr. J. T. Wallis, now Assistant Vice President in Charge of Operation of the Pennsylvania Railroad, and adopted as standard for heavy power by that road. They work in guides having two inwardly projecting horizontal ribs on each side.
Walschaerts valve gear is used, with an independent motion for each cylinder, but all controlled by one type B Ragonnet power reverse gear. The valve for the left-hand cylinder is operated from the left-hand main pin and crosshead in the usual way. The right-hand valve receives its lead from the right-hand crosshead, but the link for this cylinder is operated through a transverse shaft, by means of a connection to the left-hand cross-head. The return crank on the right-hand main pin is set to operate the valve from the inside cylinder, and this valve is given lead through a connection with the inside crosshead. The valve motion bearer is a single steel casting supporting practically the entire valve gear.
This locomotive, designed to traverse curves of 17 degrees, has flanged tires on all the wheels. Lateral motion boxes are applied to the first driving axle. The front truck has a swing bolster suspended on heart-shaped links, while the rear truck of the Delta type, and is so designed that a booster can subsequently be applied if necessary. There is a continuous equalization system on each side of the locomotive, from the leading drivers to the rear truck.
The accessories are all operated by superheated steam at a pressure of 350 pounds, except the feed-water heater and injector, which use saturated steam at the same pressure.
The tender is carried on two six-wheeled trucks, and is of the Vanderbilt type with capacity for 12,000 gallons of water and 16 tons of coal.
DISCUSSION OF TESTS
After a few preliminary runs on the road, Locomotive 60,000 was turned over to the Pennsylvania Railroad to be tested on the locomotive testing plant at Altoona.
The locomotive test plant is too well known to require detailed description. On it a locomotive under test is supported on carrying wheels which are controlled by hydraulic friction brakes so that the power developed can be absorbed, while the tractive effort is measured by a dynamometer.
On the test plant it is possible to run a locomotive continuously for an hour or more with perfect uniformity of speed and cut-off. At the same time water and coal measurements, and observations of draft and temperature, can be made with an accuracy unattainable in road tests.
While all test measurements can be made with much more facility and accuracy on the test plant, this is particularly true of indicator diagrams. In. the case of road tests, corrections are necessary for acceleration due to grades or change of speed, and it is always possible, by a change in throttle or reverse lever, to produce a card which does not in any way correspond to the speed at which the engine is running. On the test plant such irregularities cannot occur, and the indicator cards are far more reliable than those obtained in road service.
The tests made by the Pennsylvania Railroad on Locomotive 60,000 covered speeds from 80 to 200 revolutions per minute (15 to 37.5 miles per hour), and cut-offs from 50 to 90 per cent in the high-pressure, and 20 to 70 per cent in the low-pressure cylinders. The indicated horse-power developed ranged from 1500 to 4500, at which figure the capacity of the test plant was reached, otherwise a higher power could have been developed.
Maximum power was developed at 200 revolutions per minute with a cutoff of 80 per cent in the high and 50 per cent in the low-pressure cylinders. With these conditions held constant during a test run of one hours' duration, the following results were obtained
Equivalent evaporation, pounds per hour
Coal fired, total dry coal, pounds per hour
Coal fired, dry coal per square foot of grate, pounds per hour
Boiler efficiency, per cent
Steam per indicated horsepower hour, pounds
Dry coal per indicated horsepower hour, pounds
Draw bar pull, pounds
During this test the boiler pressure averaged 344 pounds per square inch, with a temperature of 683 degrees F. or 257 degrees superheat in the branch pipe. The horse-power and equivalent evaporation of this test are both higher than have been reached with any other locomotive on the test plant. They represent approximately the maximum values likely to be reached by Locomotive 60,000 in regular operation, although as stated elsewhere, they could have been exceeded if the capacity of the test plant had not been reached.
On a repeat test with the same cutoff and speed a similar horse-power was obtained with the same coal rate and a water rate of 15.4 pounds. This gives an average water rate of 15.15 pounds per indicated horse-power hour for a working rate of 4500 horse-power indicated.
The evaporative capacity of the boiler was high and so far as published records show, is higher than that of any other locomotive boiler tested at Altoona. This is due to the largo dimensions of heating surface, grate area and combustion space.
When plotted against the rate of firing per square foot of grate per hour, the boiler efficiency is well represented by a straight line ranging from about 67 per cent at 40 pounds or dry coal per square foot of grate per hour to about 53 per cent at 140 pounds of dry coal per square foot of grate per hour.
More detailed information on the boiler efficiency is given by the heat balances and by the determination of the efficiencies of heat production and heat absorption. The efficiency of heat absorption is about 82 per cent at all rates of working, while the efficiency of combustion fall off as the rate of firing increases.
Comparison of these efficiencies with those obtained from modern boilers with fireboxes of the conventional type shows little difference in the overall boiler efficiency. The tests show that the water-tube firebox has little effect on steam production. Its purpose is to eliminate the necessity for flat stayed surfaces in a high-pressure boiler.
The temperature of the steam in the branch pipe ranged from 568 degrees F. at the lowest power to 683 degrees at high power. These figures compare closely with those usually obtained with other locomotives. The superheat corresponding to the foregoing figures varies from 135 to 257 degrees.
For all cut-offs between 50/20 (that is 50 per cent in the high and 20 per cent in the low-pressure cylinders) and 80/50 and at all speeds from 15 to 30 miles per hour, 80 to 160 revolutions per minute, the water rate lies between 14.2 and 15.2 pounds per indicated horse-power hour. Even at full gear with a cut-off 90/70, the water rate is only 16.3 pounds at 15 miles per hour, and 16.6 pounds at 22.5 miles per hour.
Examination of the information available from published records shows that the best water rate on record for an American locomotive ranges from 15.5 to 19 pounds, these figures being obtained with 250 pound:-per square inch boiler pressure. The usual modern locomotive with a boiler pressure of 200 pounds per square inch and possible full stroke cut-off will usually be found to have a water rate ranging from 17 to 27 pounds per indicated horse-power hour.
It is evident that in Locomotive 60,000 the combination of high-pressure and high expansion gives a high degree of engine efficiency.
The ratio of expansion was computed by Heck's method.
Owing to the high ratio of expansion obtained in the compound cylinders of Locomotive 60,000, the pressures at the end of expansion are less than would usually be obtained in single expansion cylinders using steam of lower initial pressure. This is a factor in increasing the cylinder efficiency. At the end of expansion the steam is exhausted and loses pressure without doing useful work. This represents a loss which can be reduced by a high ratio of expansion which produces low pressures at the end of expansion.
The proportion of power developed respectively by the high and by the low-pressure cylinders, varies with the speed and cut-off. At 200 revolutions per minute and a cut-off of 80/50 when developing 4500 horse-power as above, the high-pressure cylinder delivers 1080 horse-power or 24 per cent of the total, leaving an average of 38 per cent for each of the low pressure cylinders. That is, at this speed and cut-off, the high-pressure cylinder does about one-third less work than each of the low-pressure cylinders. If the speed of 200 revolutions per minute be maintained and the cut-off shortened to 60/30 the indicated horsepower drops to 2880, of which only 145 horse-power or 5 per cent is contributed by the high-pressure cylinder. This combination of cut-off and speed does not represent conditions likely to be met in actual service, as the power developed is only slightly over one-half that of which the engine is capable.
The cylinders were designed to give equal work up to approximately 22 miles per hour, after which, as the tests verify, the inside engine is relieved with increasing speed.
These tests are interesting in showing that a drawbar pull less than the maximum capacity of Locomotive 60,000, can in many cases be obtained more economically by throttling that by shortening the cut-off. This is contrary to the generally accepted practice with ordinary single expansion locomotives, but for Locomotive 60,000 is borne out by experience in road tests. In actual service it is usually better to use the throttle rather than the reverse lever for minor reductions in tractive effort.