AN ASME PAPER ON THE ARMSTRONG-WHITWORTH LOCOMOTIVE

Here is an abstract (from RAILWAY AGE, dated January 10, 1925) of a paper presented at the annual meeting of the Railroad Division of the American Society of Mechanical Engineers by George F Jones and T Laurence Hale:

"There is great room for improvement when it is considered that a locomotive of the ordinary type has a thermal efficiency of only approximately six per cent and that doubling its, thermal efficiency would reduce the fuel consumption by half or alternatively, allow a much more powerful locomotive to be built with the present practical limits of firebox area. The replacing of cylinders by the steam turbine is an innovation, in locomotive construction, but not more so than the application Qf condensation which is rendered possibie by lts introductlon. From a thermodynamic point of view, it is evident that turbo locomotives, whatever their systems of power transmission, whether electrical or gear, largely depend for their economies in fuel consumption upon the efficiency and reliability of their condensing plant.

General Description
The front portion of the Ramsay locomotive, which is connected to the rear portion by a special universal joint, incorporates the boiler, forced draft set and driver's cab, the main turbo-alternator set and the auxiliary direct-current turbo generator being situated under the boiler. The rear portion of the locomotive is practically devoted to the condensing plant with axial fan, condensate extracting pump, etc. Room, however, has been found for the main water tank and coal bunker. Communication between the turbines and condenser is by means of a 24-in. diameter exhaust pipe which is provided with a flexible rubber connection reinforced by internal rings of aluminum.

Each portion of the locomotive carries two driving motors, each pair of motors being bolted to a center cross-bearer which carries a transmitting shaft and spur wheels. Pinions are keyed to the motor shafts and these mesh with the spur wheels, the power being finally transmitted through coupling rods from the spur wheels to the driving wheels in the ordinary manner. The spur wheel and pinion shafts are enclosed in a gear case and run in an oil bath. The gear ratio is 2.8 to 1.

The main turbine is of the impulse type and contains. nine stages. The mean blade diameter is 36 in. It IS designed for a steam pressure of 200 lb. per sq. in., and the steam IS superheated to a total temperature of 685 deg. F., exhausting to a vacuum of 27 in. The turbine is flexibly coupled to a three-phase alternator and has a speed range of 1,800 rpm at starting to 3,600 rpm. at 60 miles an hour. The three-phase alternator. is designed to develop 890 kw. at a maximum pressure of 600 volts. The auxiliary turbine is a single stage machine flexibly coupled to a direct-current generator, which provides the energy for the excitation of the main alternator poles as well as for the auxiliary direct current motors driving the condenser fan, condenser rotor, condenser extracting pump and the forced draft set for the boiler. It also supplies the necessary current for lighting the train. The auxiliary turbine operates under the same steam conditions as the main turbo set.

The boiler is of the ordinary locomotive type and the combustion chamber is supplied with air by a high speed forced draft set located in the cab. A simple locking device is provided on the fire door to prevent a blow-back, the door being prevented from opening by a safety catch when the forced draft fan is in operation.

The transmission of power from the main turbine to the driving motors is three-phase, current being supplied from the alternator to the four alternating current slip ring motors, each motor having a continuous output capacity of 275 b.hp. and one hour's rating of 360 b.hp. The following tractive force is developed at the rims of the driving wheels for the acceleration period from rest to 60 miles an hour:

Miles an hour	Tractive force
At starting	22,OOO lb
15	22,000 lb
30	11,050 lb
60	8,600 lb
60 (normal running)	6,000 lb

Design and Description of the Condensing Plant
As the success of a locomotive of this description depends in such a large measure upon the design and action of its condenser, it is perhaps not irrelevant to give a very brief review of the groundwork which influenced the adoption of the principle of evaporation as the basis of design for the present condenser. In the light of previous experience with the difficulties of recooling condensing systems, it was decided to attack the exhaust steam by direct means. It was fully realized that the alternative method to evaporation, that of direct cooling by air alone, involved the employment of large condensing surfaces and excessive fan power, and that such a type of condenser would depend for its success largely upon atmospheric conditions; and, while probably producing a satisfactory vacuum in low temperature countries, the system would be at a great disadvantage and far from satisfactory in hotter climates. Attention was, therefore, turned towards evolving a suitable condenser on the direct cooling system based on the evaporative principle as being the system to successfully meet the atmospheric conditions of all countries.
In design, the ordinary evaporative condenser has progressed but little and still remains practically as originally conceived; such test results as existed were unreliable and it was, therefore, necessary to carry out a series of preliminary experiments on small scale condensing apparatus with fans to produce a current of air and so intensify the evaporative effect. The importance of maintaining a thin and unbroken water film upon the condensing surfaces was easily demonstrated and, of the numerous methods and contrivances tested with a view to producing satisfactory water filming of the surfaces under a blast of air, the simple method of completely immersing the surfaces in water before exposing them to the air current was found to give the most reliable and proper film effect. Repeated tests on a small condensing plant proved the type to be exceedingly economical in water consumption, in practice approximately only one pound of water being evaporated to condense one pound of steam. The fan power required was reasonably lowwhile the rate of heat transmission was found to be moderately high and sufficient to bring the condensing surface well within the practical limits.

Further experiments were carried out on a plant containing some 400 sq. ft. of surface. For the sake of simplicity, the condensing surfaces were composed of ordinary brass condenser tubes and, as a natural development to facilitate the process of filming, they were arranged in the form of a circular cage, or hollow drum. The drum, supported between bearings, was rotated in a tank containing water, the tubes passing through the water as they rotated. The condenser was supplied with air by an axial fan and was tested in conjunction with a steam regenerator and the necessary wet air pump, water filming of the surfaces and resultant evaporation taking place successfully. The promising results from this experimental work led to the design and construction of the present locomotive condenser.
Ordinary condenser practice was observed in the con- struction of the drum which consists of an annular nest of standard % -in. diameter brass condenser tubes ferruled into two headers. The exhaust steam entering one header is condensed, and the resultant condensate is collected and drawn off from the other header and returned to the hot well by the rotary extraction pump as hot clean feed water for the boiler. The trunnions of the respective headers are fitted with air tight glands of the steam sealed self-adjusting type, and this design of gland has given satisfaction in resisting air leakage into the condenser.
A small motor, driving through a spur gear, turns the drum which is housed in a sheet metal casing, the bottom of which forms a tank containing water fed from the main tank for purposes of filming, and a pneumatic float maintains the water at a constant level. The condensate extracting pump is of the ordinary rotary condenser design, while the air pump is of the steam ejector type and has two stages. This pump is supplied with steam from the bOiler through a reducing valve.

Control of Power and Speed Regulation
Before starting the locomotive, the auxiliary turbine is run up to a speed of 3,000 r.p.m., thus providing excitation for the main alternator and energy for the motor-driven auxiliaries. The main turbine set is then run up to half speed; viz, 1,800 r.p.m. At this period the motors are connected in cascade by the master controller in the driver's cab. Then the locomotive may be started. It is well known that when a turbine speeds up from rest to full speed, its torque decreases in the ratio of two to one, and when passing through the period of half speed its torque is one and one-half times the normal and this is the torque of the main locomotive turbine when running at starting speed; namely, 1,800 r.p.m. Again, two alternating current motors when connected in cascade and running at half the alternator speed, have twice the turning moment that they have when connected in par- allel with the same power consumption. Therefore, with the driving motors in cascade and the main turbine running at half speed, the torque from rest to quarter speed will be two times 1.5, or three times the normal torque. The motors now being connected in parallel with the turbine running at half speed, the speed of the locomotive increases from one quarter to one half speed, and the torque becomes 1.5 times the normal. The turbine speed is then increased to the maximum and the torque drops from 1.5 times the normal to normal. In controlling the speed of the Ramsay locomotive from rest to 60 miles an hour, the following sequence of operations is observed:
After the main and auxiliary turbines have been brought to speed by means of the hand wheels in the cab which control the steam inlets, all control of the locomotive is carried out electrically by means of the master controller. To start the locomotive, the controller wheel is moved to the first notch, thereby closing the excitation circuit of the alternator and connecting the driving motors in cascade with resistance wholly in circuit. Further movement of the control wheel cuts out resistance until a first running position of 15 miles an hour is obtained. If a greater speed is desired, the controller wheel is further moved round and changes the motor connections from cascade to parallel, and the excitation circuit being again closed, the motors once more operate under current, resistance being cut out until a second free running speed of 30 miles an hour is reached.
Further increases of speed are obtained by moving the controller wheel round, step by step, whereby the setting of the main turbine governor is correspondingly altered, that is, the speed of the turbo-alternator is increased and thereby the periodicity. In this manner the speed of the locomotive can be increased from 30 to 60 miles an hour. A reduction in the speed of the locomotive is obtained by turning the controller wheel quickly back to the zero position, thus observing the reverse succession of operations to those of starting up to full speed. The excitation circuit being opened, the motors are without current and ready for starting up again in cascade.
Reversing the locomotive is, of course, effected by reversing the driving motors in the ordinary way. The illustrations show the general arrangement of the front portion of the locomotive. The resistances, which are of the grid type, are arranged under the running plates on either side. Both vacuum and Westinghouse brake equipment is used.

Principal Dimensions And Proportions

Length overall	69 ft. 7 in.
Total wheel base	59 ft. 4 in.
Rigid wheel base	16 ft. 4 in.
Drivlng wheel diameter	48 in.
Height from rail to center line of boiler	10 ft. 3 in.
Maximum width	9 ft. 0 in.
Total heating surface of boiler	1,543 sq. ft.
Grate area	28 sq. ft.
Tractive force at starting	22,000 lb.

Shop and Main Line Testing
Shop tests, to ascertain the reliability of the special electrical control were carried out before the locomotive was given actual running trials. In addition, several main line trials were made when the locomotive hauled heavy trains without difficulty, a vacuum, ranging from 80 to 95 percent, being regularly attained and held. Pronounced smoothness of running was evident, due to the constant and even turning moment exerted by the driving motors.
At no time during the run did the temperature of the condenser exceed 135 degF which corresponds to a vacuum of 25 in. of mercury. Improvement in the vacuum during easier periods of the run were noted. The work of driving and firing was carried out by ordinary railway employees and, as all the work in speeding up the locomotive is performed electrically, the duties of the engineman, so far as controlling the locomotive is concerned, are confined to the turning of the controller wheel, while the duties of firing are not as onerous as those connected with the ordinary locomotive.