The metre gauge Royal State Railways of Siam took early steps to dieselise their railways due to the serious inroads being made into the nation's lumber supplies by their fleet of wood burning steam locomotives. Despite the necessity of now having to import oil for the new diesels, several diesel orders were placed, the first in 1927 for two 180hp diesel mechanicals built by the Swiss Locomotive Co for shunting and local traffic work around Bangkok. Further orders followed in 1931/32 including one 1,600hp heavy goods locomotive, six 1,000hp express passenger locomotives and the first of three orders for Sulzer powered locomotives as follows:

1931/32 six 450hp machines, # 501 - 506
1945/46 four 735hp machines, # 651 - 654
1950/51 three 960hp machines, #561 - 563

Additionally six 150hp railcars were purchased. All the orders upto 1932 were placed under requirements laid down by the CME Mr H A K Zachariae, details of the designs were worked out by the builders - Frichs & Sulzer Brothers.

A1A-A1A 450hp locomotives of 1931/32 delivery 501 - 506

In 1930 six 450hp diesel-electric locomotives were ordered from Sulzer Brothers, with the first of them undergoing tests in Switzerland during the summer of 1931. Design specifications were to the order of Sulzer Brothers, the mechanical portions were constructed by Henschel & Sohn AG, Kassel and electrical equipment supplied by Ateliers de Construction Oerlikon.

The Sulzer engine was an eight cylinder four stroke cycle trunk-piston type (8LV25) with a maximum output of 450hp at 700rpm. Cylinder dimensions were 250mm x 310mm being cast in two blocks of four bolted together to form one rigid block. The light main frame is of cast steel. The connecting rods were of chromium-nickel steel, the uncooled pistons were aluminium. Operation of the engine was by direct airless injection of fuel on the precombustion chamber principal which required low injection pressure and fairly large nozzle holes. Each cylinder had its own readily accessible fuel pump, situated between the pushrods of the inlet & exhaust valves, the pumps were driven off the main camshaft. Fuel delivery was controlled by a centrifugal governor set to keep the engine running at a constant speed.

The Sulzer 8LV25 engine.

Starting the engine was by means of motoring the main generator from a battery. The main generator was self ventilated and provided power to four series-wound nose suspended traction motors worked in parallel, also self ventilated, using reduction gearing to transmit power to the wheels. The auxiliary generator was directly coupled to the main generator and provided power for various auxiliary machines, the battery & for exciting the main generator.

Cooling of the water and oil was by the use of variable speed electric fans drawing air through two side mounted radiators. Svenska iron-nickel accumulators were located in the front and rear sections of the locomotives.

The locomotive has been so designed that it can be operated by one person. Instruments in the cab include a speedometer, a tachometer, a watt-meter displaying the main generator output and an ammeter for the traction motors. An instrument showing the state of the governor allowed the driver to detect any problems with the cylinders and also contained a device to monitor the flow of the cooling oil & water. Maximum speed was 37.5 mph (60km/h), the maximum for the main lines at that time.

Braking was by vacuum or handbrake whilst compressed air sanders were fitted on the bogies.

Although the vast majority of the locomotive frame and structure was made of metal the engineroom floor was covered with teak wood.

A builder's view of one of the 1931 built machines.

The first locomotive was tested between July 6th & 20th 1931 on the Landquart - Chur - Disentis line of the Rhaetic Railways. This route was about 73km in length with an elevation gain of just over 600 metres. Eleven round trips were made totalling 763 miles (excluding mileage through shunting). Total fuel consumption for this period, including shunting work, was 3,410lb. Starting and acceleration tests were also carried out. After stopping the train comprised of five bogie coaches (120 tons?) on a gradient of 1:37 with 100m radius curves a speed of 19mph was reached after a maximum of 35 seconds, recorded fuel consumption was 0.035lb per ton-mile. About the tests 'The Engineer' reported "from our own observation we should imagine the results must be very satisfactory alike to the purchasers and the builders of the locomotive".

	A fine view from some Sulzer publicity material of one of the 1931 built machines under test in Switzerland.
	The spartan cab furnishings are revealed in this ex-factory view. The cab layout is very similar to a number of locomotives built during this period.

In service these locomotives worked passenger trains between Bangkok - Pitsanulok/Chiangmai (the northern line) and Bangkok - Hua Hin (the southern line). All six locomotives had each accumulated at least 700,000km prior to Siam entering World War Two. The war took its toll on the locomotives due to a reduction in maintenance and the lack of availability of spare parts. During the war one of these machines received a direct bomb hit leading to its withdrawal. After the war the remaining locomotives were returned to service as spares were shipped in during the early 1950's. As newer machines were received these early Sulzers were transferred to the Maeklong line, where 501 & 504 were still in service during 1977, one them lasted substantially longer.

(Below) Publicity views include two (left & center) taken from an advert from 1935 featuring the first order of Sulzer powered locomotives to Siam, whilst (right) shows No.503 in service at Bangkok.

At least two of these locomotives saw service into the 1990's under the ownership of the Jalan Prathan Cement Company at their Ban Sa plant near Ban Cha-am - Km 203 - on the SRT's southern line. A branch line connected with the station to their plant. The two locomotives were 504 (21828 – 1931) and 505 (21829 – 1931). 504 was noted in a shed, perhaps operational whilst 505 was plinthed near the works office.

Bo-Bo 735hp locomotives of 1945/46 delivery 651 - 654

For the longer and heavier graded southern mainline from Bangkok to Singpore (750 miles) & the northern mainline from Bangkok to Chieng Mai (470 miles) the RSR looked for more powerful locomotives. The good service record of the first order of Sulzer powered locomotives led to the placing of a further order with Sulzer Brothers.

Sulzer were able to provide a more powerful engine in this second order (430hp v 735hp), and were able to construct the locomotives using newer weight saving methods, allowing for the use of only four axles to carry the locomotive weight, rather than six axles as in the first order. The mechanical portion was built by Henschel & Sons, Kassel, the electrical equipment by Ateliers de Construction Oerlikon, whilst Sulzer, Winterthur built the power unit.

The 6LDA25 power unit was a six cylinder four stroke machine of conventional Sulzer construction. Cylinder diameter was 250mm, piston stroke was 320mm. The one hour output rating 735hp at 850rpm, continuous rating was 650hp at 750rpm. Tractive effort was 9,200lb at 17.5mph (one hour rating) or 6,800lb at 22.5mph (continuous rating).

The heart of the machine, the Sulzer 6LDA25 looking towards the radiator end of the locomotive.

The outward appearance of the 1945/46 deliveries differed somewhat from that of the 1931/32 order. Weight saving was achieved by replacing standard rolled sections with bent sheet metal parts riveted or welded. Much welding was used to create the main structural members and the bogie frames. For instance the horizontal middle and upper transoms, when fabricated using the latest procedures were forty percent lighter with a sixty five percent higher bending resistance.

One major design change from the first order was the position of the intakes for receiving air for the traction motors. In the first order the cooling air was drawn from underneath the locomotive body. This location caused inordinate amounts of dust to be drawn in causing serious operating problems for the traction motors. For the second order air was drawn in from the region of the cab roof, which also provided for improved air circulation within the cabs.

Termite damage to the wooden surfaces in the cabs was mitigated through the use of impregnated plywood or teak.

Testing of the first locomotive took place in June 1942 over the Rhaetic Railways hauling loads up to 182 tons. Delivery to Siam did not begin until hostilities ended in 1945.

A view of one of the second order of locomotives for Thailand, seen here under test in Switzerland - this view being used to advertise Sulzer powered diesel locomotives and railcars. As usual the locomotives of this period sport a quite considerable builder's plate, mounted midway along the side of the locomotive.

These four locomotives ended their days working the Maeklong line, most definately 651 & 654, probably lasting in service until about 1989.

Photograph courtesy Robert M. Boer of Rail Asia
Some forty years after delivery 651 was still operational and photographed in a corner of the Mahachai depot on March 23rd 1986.

A1A-A1A 960hp locomotives of 1951 delivery 561 - 563

During 1951 three locomotives were delivered to the Royal State Railways of Siam for use on routes between Bangkok & Padang Besar (625 miles) and Bangkok & Chiengmai (465 miles). Gradients on the southern mainline are at a ruling 1:100 with short distances of 1:50, curve radii vary from 590ft on the main line to 510ft on sidings and through points. The maximum axleloading was 12 tons, maximum speed limit was 40mph. Temperatures varied between 50F & 104F, with a maximum altitude of 2,000ft. On the northern line gradients were more severe with stretches of 1:42 & 1:37. Trailing loads were 420 tons over the southern route and 250 tons on the Chiengmai line.

With Sulzer Brothers Ltd again as the main contractor all specifications were to their requirements, electric transmission equipment was provided by Maschinenfabrik Oerlikon, the mechanical portion completed by Henschel & Sohn GMBH. Particular attention was paid to the maximum axle load requirement, the A1A-A1A wheel arrangement being preferred after much study. In order to simplify matters for the Siam railway authorities much standardisation took place between these units and the earlier 735hp Bo-Bo machines. Although more cylinders were involved in the newer engines many of the components were of the same dimensions. The electrical control equipment, driving controls, wheel centres, tyres, axleboxes, springs, brake blocks and other mechanical portions were the same as were the basic lines of construction.

The power unit was a Sulzer pressure-charged 8LDA25 type set to give 960hp at 850rpm at the one hour rating, or 860hp at 800rpm continuous rating, cylinder dimensions were 9.85in by 12.6in (250mm x 320mm). It was of the usual welded construction of cylinder block, crankcase & bedplate made up of mild steel & cast steel components. Dry weight for the engine was 18,240lb. Charge air was provided by a Sulzer exhaust gas turbo blower with the usual plain bearings for the shaft.

The Oerlikon main generator was mounted on the common welded steel subframe. Continuous rating was 800rpm, 1,000volts, 550amps or 800rpm, 630volts, 860amps, the one hour rating was 800rpm, 497volts, 1070amps, the maximum rating was 850rpm, 1060volts, 1680amps. The auxiliary generator, of 33.7kW is of the overhung typeand supplied the main generator excitation current; motors for the cooling water pump, radiator fan, exhauster, air compressor, rotary voltage converter and for charging the batteries.

The four traction motors were self ventilated and nose suspended, grouped in parallel. Each motor was rated at 121.5kW, 268amp, 497volts, 700rpm - one hour rating, or 125.5kW, 215amp, 1000rpm, 630 volts - continuous rating. Ventilating air was drawn in from behind the cabs

A Sulzer automatic field regulator control allows the driving controller to regulate the engine governor, setting the engine speed at predetermined values; the main generator excitation provides a constant torque on the engine. Eight speed-torque loadings are available from 470 to 850 rpm and from idling to 960hp. Overloading is prevented in all circumstances, shutdown will also occur if cooling water or lubrication oil pressures fail or become too high.

The low required axle loading led to the complete welding of the locomotive body, bent and pressed sheet steel were used for all horizontal & vertical parts, providing much additional stiffening to the framework. The complete body framework is welded and riveted to the underframe.

The bogie frames were completely welded and supported on SKF roller bearing axleboxes through overhung laminated springs. Each bogie carried one brake cylinder, each motored axle had two brake blocks per wheel, connected through compensated rigging.

Trial runs on the Rhaetian Railway provided some interesting data, not only because of the steep grades (up to 1 in 25) combined with sharp curves but because this was a locomotive built for a tropical climate under test in winter conditions. Runs were made first between Landquart and Ilanz, 26 miles with an average grade of 1 in 200; and with a ruling grade of 1 in 100 for five miles, curved almost throughout at 262ft - 985ft radius. Trailing loads up to 300 tons, were made up of sixteen bogie coaches; on the 1 in 100 grade with the curves a sustained speed of almost 27mph was maintained, the diesel engine working on its one hour output. On the Ilanz route grades of 1 in 72 with curves of 262ft radius were featured. Landquart is at 1,730 ft, Ilanz is at 2,300 ft. Fuel consumption for the return trip was equivalent to 0.021lb per gross ton-mile.

Further trials conducted over the 13.25 miles between Landquart & Kublis, rising all the way at an average of 1 in 69 and with a ruling grade of 1 in 25, were run with 155 tons trailing. Speed up the ruling grade was 25mph at the beginning but fell to 13mph after 0.62 mile with the controller on notch 9, equal to the diesel engine continuous output. Fuel consumption on the Landquart - Kublis section was 0.033lb per gross ton-mile.

Dimensions for the Bo-Bo & A1A-A1A locomotives

	1931 A1A-A1A	1946 Bo-Bo	1951 A1A-A1A
Weight, empty/full	??/60tons	43.5/46.5tons	54/58tons with 2,700 litres of fuel
Minimum adhesion weight	43tons	44.5tons	44tons
Maximum Axle Loading	??	12 tons	12 tons
Starting Tractive Effort	20,680lb	20,000lb	30,900lb
Tractive Effort - Continuous	??	6,800lb @ 22.5mph	12,800lb @ 19mph
Tractive Effort - One Hour	9,130lb @ 12.8mph	9,200lb @ 17.5mph	17,600lb @ 14mph
Tractive Effort - Full Power & Max Speed	??	??	6,600lb @ 40mph
Wheel Diameter	36in -driving, 30in carrying	3.00 ft	3.00 ft
Bogie Wheelbase	9ft 10in	7ft 10.5in	9ft 10in
Distance between bogie pivots	24ft 3in	22ft 7.375in	25ft 7in
Length over buffer beams	44ft 6.75in	37ft 1in	42ft 0in
Maximum width	??	9ft 1.5in	9ft 2in
Maximum height	??	12ft 6.25in	12ft 6.5in

The following is an extract from the Diesel Railway Traction journal, July 1951 detailing additional testing of one of the locomotives awaiting shipment to Siam

Testing of one of the new diesels over the Rhaetian Railways Landquart-Klosters-Davos route included operation under severe winter weather conditions. In fact the day after testing the route was blocked for a week due to heavy snowfall & avalanches.

Timings and loads of these recent test runs were adjusted so that the continuous output, at least of the diesel engine should be required more or less all the way from Lanquart to Davos-Wolfgang, a 44km (27.5mile) metre gauge route entirely uphill, with ruling grades of 4.5 & 4.52 percent (1 in 22), with one 800 metre stretch of 5 percent (1 in 20) just south of Klosters. Throughout the steepest grades there is a constant succession of curves of 100 to 300 metres radius. Between Klosters & Davos the 1 in 22 grade, with the 1 in 20 section also, extends continuously for 10km (6.2 miles) with only the intermediate platform lengths as intervening levels sections.

On controller notch 10, corresponding to the one hour diesel engine output, speed was 34kph (21.1mph) at the beginning of the 1 in 22.25, and fell to 32-33kph (19.8-20.5mph). Using controller notch 9, corresponding to the continuous output of the diesel engine the speed maintained over the same section was 30.5-31kph (19.5mph). Trailing load was three bogie coaches weighing 60 tonnes. From Landquart to Kublis, with a maximum grade, short in length, of 3.46 percent (1 in 29) trailing grade, the load was eight bogie coaches weighing 157 tonnes. From Kublis to Kosters with 4.26 to 4.37 percent (1 in 23.5 to 22.75) grades, trailing load was four bogie coaches weighing 80 tonnes; and from Klosters to Davos-Wolfgang with continuous 1 in 20 to 1 in 22.25 grades, three coaches weighing 60 tonnes were hauled. Between Landquart & Klosters the electrical equipment was loaded slightly above the continuous rating; and on the Davos - Wolfgang route the throughout average load was just equal to the continuous rating.

Test run of 960hp Sulzer diesel locomotive

Station	Time	Distance - kilometres	Height above sea level in feet	Maximum Grade	Sustained speed - mph
Landquart	dep 9.10	0.0	1,725	1 in 25	21
Kublis	arr 9.51 - dep 9.55	21.5	2,665	1 in 23.5	21
Klosters	arr 10.28 - dep 10.30	32.5	3,910	1 in 23	21
Davos-Wolfgang	arr 10.54	43.6	5,330	1 in 20	19.2

The Rhaetian Railways imposed the following speed limits on this route:
Landquart - Kublis: 55/65kph (34/40.5mph)
Kublis - Davos: 40/42kph (24.8/26mph)

In general the diesel engine was developing 850 - 950hp from Seewis to Davos-Wolfgang (23 miles).

Fuel consumption over the return trip between Landquart & Davos-Wolfgang was 11.3gr per tonne-km (0.045lb per gross ton-mile). The trials were of exceptional interest not only because of the sound behaviour in heavy snow conditions of a locomotive designed for tropical service, but also because of the way steady speeds of 18.5 to 21mph were maintained up gradients exactly twice as steep as the maximum to be encountered in Siam, and at heights up to 5,330ft above sea level at Davos.

A report from 1960 indicates that all of the locomotives from the second & third order were in service as part of Siamese State Railways fleet of sixty five diesel locomotives. Three pre-war diesels were included in these totals, presumably this must include the two remaining locomotives from the first order.

Sources:
Railway Gazette, August 7th 1931, Diesel Railway Traction April 1946 & February 1951.
The Railways of Thailand - Roel Ramaer, White Lotus, Bangkok 1994.

Page added April 21st 2003
Page updated January 3rd 2009

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