This locomotive is one of the most obscure I have ever researched, but here are the facts I have assembled so far.

Four of these metre-gauge locomotives were built by the Sentinel Waggons Works Ltd of Shrewsbury, England; the first was sold to the Belgian State Railway in May 1934. Three more were produced for the Société National des Chemins de Fer en Colombe, in Colombia, South America, and these were first shipped to Belgium for testing on metre-gauge track there, and then on to South America in June 1934.

These locos were specially designed for the sharp curves and steep inclines of Colombia, and intended to pull 200-ton passenger trains up gradients of 2%. The minimum track radii are reported to have been 56 to 80m. Power output was more than 600HP, with a tractive effort of 17,500 lbs, or 7940kg. Each had two six-wheeled bogies, with a Doble steam-motor driving each axle, so there were six motors in total. If one motor failed it could be disconnected from its axle in a few minutes, its steam supply cut off by an isolating valve, and the journey continued.

The boiler was a Woolnough water-tube type, working at no less than 550 psi, with a heating area of 45 m2 (489 ft2); the design cetainly qualifies as a high-pressure locomotive. It was a marine-type 3-drum watertube boiler, first patented in February 1929 by W H Woolnough. A later patent (No 388,799) in August 1931 was jointly applied for with the Sentinel Waggon Works. This type of boiler was used for several railcar and locomotive projects, having a much greater steam-raising capability than the small boilers Sentinel used to power their steam-wagons. The Woolnough boiler for the Colombian locomotives was the largest that Sentinel ever built.

Left: The Colombian steam motor locomotive. This photograph appears to have been taken in England, judging by the scenery. That is a very English-looking bridge in the background. The front of the locomotive is on the right. Apologies for the poor picture quality; images of this machine are very hard to come by.

Left: The Colombian steam motor locomotive: side elevation. Dimensions are in millimetres.

Left: The Colombian steam motor locomotive. This photograph and the one below were taken during the trials in Belgium. You can't see it at this scale, but the wagon in the lower picture has "Maissin" written on it. Maissin is a Belgian village, and once a depot on the Poix-Paliseul metre gauge tram line in the Ardennes. The line opened in 1903 and closed after 1955. Belgium once had extensive metre gauge tramways, more than 4000km in length, and known as the Vicinal network. They were almost all run by an organisation called the NMVB. (De Nationale Maatschappij van Buurtspoorwegen) The SelfSite brings you the details! Maissin information very kindly provided by Johan De Groote.

Left: The Colombian steam motor locomotive. In any case, the vegetation does not look Columbian, insofar as I am any judge. Apologies again for the poor picture quality.

Left: The control-room of the Colombian locomotive. The two pedestals on each side carry duplicated throttle levers (on top) and cut-off control cranks. (on the sides facing the camera) Next to each throttle lever is a linear scale indicating the cut-off that has been set. These controls were linked and allowed the locomotive to be driven from either side. The central handwheel next to the three gauges is the steam stop-valve. The six-way lubrication distributor can be seen to the left, near the window.

The boiler was mounted in the centre of the locomotive. There was a 960 gallon water tank to the front, and another 240 gallon tank at the back. The coal was carried in a bunker just behind the cab; it could hold 3 tons.
The boiler was fed by a Weir direct-acting feedpump, with an injector as backup.

Left: The Colombian locomotive in Belgium. Taken from the coal-bunker end. The picture quality is, I'm afraid, pretty dire. But since photos of this machine are very rare- here it is. From The Railway Gazette, June 15, 1934

Left: One of the bogies of the Colombian locomotive. Three of the flexible/articulated steam pipes to the motors can be seen in front of the side towards the camera. From The Railway Gazette, June 15, 1934

Left: One of the bogies seen from above. Unfortunately no details of the steam motors are discernible. From The Railway Gazette, June 15, 1934

Left: The front elevation of the Colombian locomotive. Showing the upper steam drum and the two lower water drums of the Woolnough water-tube boiler. From The Railway Gazette, June 15, 1934

Above: The compound Doble steam-motor in plan & elevation. From Engineering, 1933 or 1934

Each steam- motor was a two-cylinder double-acting compound type, designed by a team headed by Abner Doble, one of the founders of an American company called Doble Steam Motors, which had succumbed to the Great Depression. Abner Doble came to England to work for Sentinel while his brother Warren was doing similiar work at Henschel in Germany. The engine was almost identical to the design used to power a Sentinel railbus, four of which were supplied to the Southern Railway in March 1933.
The cylinders had diameters of 4.25in (HP) and 7.25in (LP) with a 6in stroke. Piston valves were driven by a version of Stephenson's link motion. There were amply-sized relief valves at each of each cylinder to prevent damage if water was trapped by the pistons. The crankshaft drove the main axle through reduction gearing of 2.74:1, and roller bearings were fitted to the main axle, the crankshaft, the big ends, and the eccentric straps. These parts were splash-lubricated by the oil in the partly-filled crankcase, while the cylinders were force-lubricated by a mechanical lubricator, via a six-way distributor in the cab.

Left: The regulator of the Colombian locomotive. This throttle valve was located in front of the right-hand control pedestal. It was of unusual design, as it had to handle steam at 550 psi without being impossibly stiff. The first movement of the throttle lever opened a central pilot valve, admitting steam to the underneath of the poppet valve and relieving the considerable force on it that kept it firmly shut. Further movement opened the poppet valve 1/8 in before the piston-like extension to the left began to uncover the six ports leading to the steam-motors. Thus the seat of the main valve was not scored by the flow of steam. God is in the details.

Left: The Woolnough water-tube boiler fitted to the Colombian locomotive. The boiler had brick partition wall which divided its interior into a firebox at one end and a smokebox at the other, the hot gases being obliged to travel through the water-tubes in the side flues. The superheater tubes were placed between the water-tubes and the boiler casing, to keep the latter from overheating. The cylinder to the left of the chimney is the feedwater heater. Air passed between the boiler casing and the exterior bodywork, cooling the former. This air was then taken to the underneath of the grate, giving a measure of pre-heating.

Left: The Woolnough water-tube boiler viewed from the other side, with the covers removed. The sinuous superheater tubes can be seen on the outside, with the water-tubes behind them.

I have so far failed to discover any information at all as to what happened when these remarkable locomotives reached Colombia. The likeliest outcome, I fear, was that local skills were unequal to the task of maintaining a complicated twelve-cylinder locomotive, and as soon as things began to go wrong, they were shunted into sidings and left there. At any rate, there were no more orders.
Christopher Wilkinson, in his book "Narrow Gauge In Colombia" (Trackside Publications) says that there are no known photographs of the locomotives working in Colombia, that their history there is unknown, and that it is most likely that they were set aside during the Second World War, when spare parts became unobtainable.

This seems a great shame. While it is impossible to comment on the performance of the locomotive in the absence of any information on its running, Sentinel were a company who knew what they were about, and it seems to me a most ingenious design.

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