Central South African Rack 4-6-4RT

Numbers 995 and 996 of the CSAR were two 4-6-4T rack locomotives specified by P.A. Hyde and built by Vulcan Foundry in 1905. They were intended for the section between Waterval Onder and Waterval Boven that also included a tunnel, so that they also required condensing apparatus. The specification called for bar frames and only two 18-inch cylinders with a long stroke of 30 inches which powered the adhesion wheels and the two rack wheels at the same time.

As opposed to the specifications, Vulcan Foundry chose to use a total of four cylinders with a stroke of only 20 inches for independent rack and adhesion drive. The driving axles were mounted in outside plate frames to provide space for a frame that held the two rack wheels. This was also the cause for the long wheelbase between the first and second driving axles. For stopping on the downward runs, they had a Le Chatelier counter-pressure air brake.

As the dimensions of the boilers had originally been specified for only two cylinders, they quickly reached their limits when both sets of cylinders were used at the same time. In the result, the CSAR continued to use older rack locomotives on this line and as early as 1906, the inside cylinders and the rack wheels were removed. Now, their wheel arrangement meant that they had a small adhesive weight compared to the total locomotive weight. The SAR integrated them into their roster, but withdrew both in 1915.