DR Class 99.23-24

The engines of DR Class 99.23 are metre gauge tank locomotives, that were procured by the Deutsche Reichsbahn (DR) in East Germany from 1954 to 1956. When they entered service they had operating numbers 99 231–99 247. Today they are numbered 99 7231–99 7247.

History
A total of 17 locomotives were bought by the DR between 1954 and 1956 for the railways of the Harzquerbahn and Brockenbahn, and for the line from Eisfeld to Schönbrunn to replace much of the outdated fleet. Four locomotives were built for the USSR in 1956, but their ultimate fate is unknown. The first seven units (99 231 to 99 237) were originally equipped with two Krauss-Helmholtz bogies. Due to problems with curve running, the engines in the second series were given Beugniot levers between the first and second coupled axles in addition to the Krauss-Helmholtz bogies (according to other sources also a Schwartzkopff-Eckhardt II bogie  ).

The locomotives of the first series were subsequently modified with Beugniot levers, some in the early 1960s, others in 1973/74 (on the Harz lines). The thinner wheel flanges of the driving wheels were completely removed later to achieve better curve running, resulting in the second series not having a rigid wheelbase. The drive was applied to the third coupled axle, the locomotives had Heusinger valve gear with unsprung Müller balanced slide valves and, later, Trofimoff valves.

These Neubaulokomotiven were a fully welded development of the standard locomotives (Einheitsloks) of the DRG Class 99.22. In contrast to those, the 99.23-24s had mixer-preheaters and plate frames. However, the latter caused maintenance difficulties from the outset due to cracks and distortion. 10 locomotives (99 7232, 7240, 7245, 7239, 7236, 7234, 7237, 7241, 7243, 7247) were equipped from 2004 onward with a redesigned plate frame and 5 of those (99 7232, 7240, 7245, 7239, 7236) with new, welded steam cylinders. The 17 DR engines are all extant and based in the Harz; some however are no longer working.

The 17 German engines were converted to primary oil-firing between 1977 and 1983, and together with the DRG Class 99.22 are the most powerful German narrow gauge steam locomotives ever constructed. They were later converted back to coal-firing and are primarily used on the line up to the Brocken from Wernigerode.

Their operating numbers changed from 99 231 et seq to 99 7231 et seq on the introduction of computerised numbers in 1970 and then again to 99 0231 et seq on conversion to oil-firing. The computer numbers are still valid because the HSB retains those allocated in the 1970 DR renumbering scheme.

The engines can carry 4 t of coal and 8000 L of water.

Locomotives

 * 99 7231: out of service since 2001
 * 99 7232: working, new frame
 * 99 7233: out of service since 1999
 * 99 7234: working, new feame
 * 99 7235: out of service since 2020
 * 99 7236: working, new frame
 * 99 7237: working, new frame
 * 99 7238: working
 * 99 7239: working, new frame
 * 99 7240: working, new frame
 * 99 7241: working, new frame
 * 99 7242: out of service since 2010
 * 99 7243: working, new frame
 * 99 7244: working, undergoing conversion to oil-firing
 * 99 7245: working, new frame
 * LKM 134023: built for & lost in the USSR
 * LKM 134024: built for & lost in the USSR
 * LKM 134025: built for & lost in the USSR
 * LKM 134026: built for & lost in the USSR
 * 99 7246: out of service since 1996
 * 99 7247: working, new frame