Impressive cylinder block with high and low pressure cylinders and the corresponding valve boxes of the four-cylinder steam rack locomotive HG 4/4 # 704 of the Furka-Bergstrecke steam railroad (DFB). This cylinder block could not be used for the refurbishment of the HG 4/4 # 704 due to heavy wear, so the one from locomotive 706 was used. The HG 4/4 # 706 was built in 1929 by Maschinenfabrik Esslingen according to SLM plans, had remained in Vietnam during the “Back to Switzerland” campaign in 1990 and the individual parts (frame, cylinder block and wheelsets) only arrived in Switzerland via the port of Haiphong in 1998. Below are the two high-pressure cylinders for driving the four drive axles, above are the two low-pressure cylinders for driving the two gear wheels. It is interesting to note that the high- and low-pressure cylinders have the same diameter of 455 mm, but the cogwheel drive runs twice as fast as the adhesion drive. The gear drive consists of two coupled intermediate countershafts, which are mounted above the driving gear shafts and drive them via a reduction ratio of 1:2. The entire gear drive is mounted in the frame and is therefore part of the sprung mass; it can be adjusted in height to compensate for wear on the drums. This single-gear design allows the high-pressure and low-pressure cylinders to have the same diameter despite the significantly different volume flow. The additional gear reduction also means that the rack and pinion motor runs at twice the speed and in the opposite direction to the adhesion motor in rack and pinion mode. The cylinders on the high-pressure side each form a single casting with their slide boxes, while the two cylinders and slide boxes on the low-pressure side are combined into a single casting. The entire cylinder block therefore consists of three parts, which are bolted to the locally reinforced frame. All cylinders are fitted with piston slide valves. This cylinder block of locomotive 704 was visually refurbished in the Uzwil workshop and is now on display next to the station in Realp.
