Cab-forwards, and the Norfolk & Western A-class. Compound expansion Compound expansion, or compound, articulated steam engines like Anatole Mallet's original idea, consist of two sets of unequally sized cylinders. The smaller pair of cylinders near the cab was fed with high pressure steam directly from the boiler and then the steam was passed into a pair of low-pressure cylinders at the front, with larger diameter to offset the lower pressure, before exhausting through the smokestack. While the thermal efficiency was greatly improved through the compound use of steam in Mallet designs, the large low-pressure cylinders posed unique limitations, both in terms of loading gauge (the cylinders could only be as large as the track and track-side infrastructure allowed) and in terms of performance at speed. The large and consequently heavier pistons caused stability issues at higher speed, which generally limited compound expansion articulated locomotives to below 30 or 40 miles per hour. A notable exception to this was to be found in later iterations of Norfolk & Western Y-class 2-8-8-2s, which could and did often exceed 50 miles per hour in service as well as being one of the hardest-pulling steam locomotives ever built. The first Garratt locomotives constructed, the Tasmanian Government Railways K class were also compound locomotives, but were complicated as a result. All subsequent Garratts were simple engines only. Geared types There were various types of articulated geared steam locomotive, including: Climax locomotive Heisler locomotive Shay locomotive Willamette locomotive Other types du Bousquet locomotive Engerth locomotive Gölsdorf axle Golwé locomotive Hagans locomotive, such as the Prussian T 13 (Hagans variant) Klien-Lindner locomotive Krauss-Helmholtz bogie Luttermöller axle Electric locomotives There are several classes of articulated electric locomotives of generally two types: Three sections, where the middle part sits on the two outer parts (similar to the Garratt design), e.g. Milwaukee Road class EP-2 Swiss crocodile locomotives, :de:SBB Ce 6/8 II and :de:SBB Ce 6/8 III DRG Class E 94, :de:DRB-Baureihe E 94 Two sections which share a central or Jacobs bogie, e.g. FS Class E.636 in Italy, first built in 1940 HŽ series 1061, a derivative of E.636 operating in Croatia - also known as SŽ series 362 in Slovenia and as JŽ series 362 in Yugoslavia FS Class E.646 in Italy, first built in 1958 FS Class E.656 operating in Italy since 1975 Rhaetian Railway Ge 6/6 II in Switzerland New Zealand EW class, built by English