Prussian State 4-4-2 Locomotives in Germany

Class S 7 - Lentz poppet valves (Locobase 20738)

Data from "Four-Cylinder Locomotive with Poppet Valves", Railway Age, Volume 42, No (10 August 1906), pp. 178-179.

Railway Age reported on George Egerstorff's very first locomotive fitted with Lentz poppet valves. A Prussian State S7 compound Atlantic (Locobase 6046) was modified to test the concept and shown at the 1906 Milan Exposition. Like many other Continental designs of the time, the boiler's Serve tubes presented a large external diameter to the water and eight slender fins inside. Railways that used them typically figured them to add 50% more area to the fire side. Compared to later Prussian 4-4-2s, S7s used relatively small grates.

The departure from conventional practice lay in the valve setup housed in a chest cast integrally with the high-pressure and low-pressure cylinder on each side of the smokebox. In contrast to both slide valves and piston valves, which oscillated back and forth, the four valves in each casing were arranged longitudinally, the middle two for intake, the rear and front valves for exhaust.

Proponents claimed several advantages. The valves sealed tightly, preventing steam from excaping, eliminated water hammering because they simultaneously acted as safety valves. Friction in their action was negligible as relatively weak springs were all that was necessary to ensure their closing, valve wear was "reduced to a minimum", they were easier to lubricate. Their action reduced the velocity of steam admission by 40%, reducing the wire drawing created by the resistance of steam flowing through ports and steam passages . Hannover that their valve was especially suited handle superheated steam.

The 648's high and low-pressure cranks on each side of the engine were set at 180 degrees apart and the two HP and two LP cranks were set at 90 degrees. "In this way," the RA report claimed, "the engine is in almost perfect balance so that it runs extremely steady and at the highest speeds."

Later assessments noted that while many of the claimed advantages were more or less proved, actuation was problematic. The rods that drove the original setup were later replaced by a rotary cam mechanism, but it too suffered from

Class S 7 - de Glehn - Serve tubes (Locobase 6046)

Data from [], which is a profile of the ten locomotives of this type that were transferred from Germany in 1919 as part of World War I reparations, and

from Maurice Demoulin, Locomotive Actuelle ... (Paris: Librairie Polytechnique Ch.Beranger, 1906), p 217-218.

Produced by Hanomag and Grafenstaden.

There were two versions of this four-cylinder compound design, differing in the compounding system used. Five of the de Glehns had the ribbed Serve tubes and are shown here; the others had smooth tubes and are described in Locobase 9183.

Regardless of tube type, the de Glehns had a more complicated operation that led to the KPEV procuring many fewer of this design than of the von Borries design. The von Borries variant is profiled on Locobase 1262.

Class S 7 - de Glehn - smooth tubes (Locobase 9183)

Data from Maurice Demoulin, Locomotive Actuelle ... (Paris: Librairie Polytechnique Ch.Beranger, 1906), p 206-207, amended by "Four-Cylinder Compound Locomotive, Prussian State Rys", The Locomotive Magazine, Vol IX (3 October 1903), p. 204. See also Dr. R. Sanzin, "Die Lokomotiven auf der Intertionalen Austellung in Mailand 1906, 5. 2/4 gekuppelte vierzylindrige Verbung-Schnellzuglokomotive mit Lentscher Ventilsteuerung er preussische Staatsbahnen ...", Zeitschrift des Oesterreichischen Ingenieur- und Architeckten-Vereines, Vol LVIII Nr. 49 (7 December 1906), p 681. Also note SACM diagram Loc. 130 from Societe Alsacienne de Constructions Mecaniques from locomotive book supplied by Dany Machi up at [] as

Diagrammes des machines SACM construites a GRAFENSTADEN (October 2007).

These were the last of the S7s, a set built by the KPEV to see if a larger firebox would raise more steam, according to Roger Hennessey's Atlantic The Well-Beloved Engine (Stroud, Gloucestershire: Tempus Books, 2002), pp. 160. The data from Demoulin include a heating surface area of 1,914 sq ft (177.9 sq m), which measured the water side of the tubes. German tube heating surface measurements - which were made on the inside of the tube -- ran between 8 and 10% less than in similar Anglo-North American locomotives.

Dr Sanzin's entry describes the Hannover prototype that used Lentz poppet valve gear. Sanzin's discussion includes some excellent diagrams of the poppet valve.

Class S 7 - von Borries with Pielock (Locobase 13575)

Data from "Four Cylinder Balanced Compound Atlantic Type Passenger Type--Prussian State Ry", Locomotive Exhibits in Railroad Transportation at the International Exposition, Railway and Engineering Review, Special Issue (1904) , pp.95-97. Frank C Perkins, "German and English Locomotives", The Technical World, Volume 1, No 6 (August 1904), p. 700. See also Charles S Lake, The World's Locomotives (London: Percival Marschall & Co, 1904), pp. 242-245. For the Pielock superheater, see the San Diego Railroad Museum's helpful faq that reproduces Llewellyn Ludy, Locomotive Boilers and Engines (Chicago: American Technical Society, 1920), pp. 63 and 74 at [], last accessed 26 March 2022; and Robert Garbe (Lesley S Robertson, editor), The Application of Highly Superheated Steam to Locomotives (London: Crosby, Lockwood and Son, 1908), pp.8, 38-40. (Thanks to Alexander Blessing for his 4 March 2022 email noting several distances and providing a link to the R&RE special issue that supplied the data.) Works numbers were 4165-4183.

Piotr Staszewski's 16 June 2021 email to Locobase claimed that Hannover never exported 4-4-2s to Russia. Locobase's investigation of Frank Perkins's article found that the caption under Figure 2, page 700 clearly read "Russian". When he looked at a builder's list for Hannover/Hanomag supplied by Allen Stanley from his extensive Railway Data Exchange collection, however, no such deliveries could be found.

Further research determined that Perkins was almost certainly referring to the Hannover batch supplied to the Prussian State Railways in the same year.

Although these are essentiallly smooth-tube compounds like those described in Locobase 1262. Charles Lake reported that some of the engines had been fitted with Pielock superheaters, a relatively low-temperature system that never threatened the growing supremacy of the Schmidt firetube design. Virtually all other superheater installations either sat ahead of the small tube bundle in the boiler, fit in the smokebox, or, in the case the ultimately triumphant Schmidt system, in a set of flues between the tubesheets.

The Pielock unit enclosed most of the tubes, forming a chamber bounded by tubesheets placed between 30" (762 mm) and 42" (1,067 mm) apart and entered by a pipe from the steam dome and exited by tube that led to a small throttle inside the dome. It was placed far enough forward of the rear tubesheet to avoid overheating.

Within the unit, vertical baffles between the ranks of tubes guided the steam entering from the steam dome so it would zig-zag before leaving the superheater, and rising up to a separate throttle that let it travel forward to the cylinders. Robert Garbe pointed out a key limitation on the system's effectiveness by observing that the superheated steam's upward journey including passage through saturated steam. Even though the two didn't mix, heat lost to the saturated steam reduced the power of the Pielock's output. (Page 38 includes several other criticisms.)

Class S 7- von Borries (Locobase 1262)

Data from Frank C Perkins, "Types of German and English Locomotives", The Technical World, Volume I, No 6 (August 1904), p.700; and [], which is a profile of the ten locomotives of this type that were transferred from Germany in 1919 as part of World War I reparations. Data amended by Christian Lindecke's German locomotive website ([], accessed 31 January 2007). (Thanks to Alexander Blessing for his 4 March 2022 email pointing out the proper deisgnation for the valve gear. Works numbers were 3768-3670 in 1902, 4094-4099 in 1903; 4156, 4165-4183, 4287-4312 in 1904; 4351-4377 in 1905; 4498-4537, 4551 in 1906

Produced by Hanomag.

There were two versions of this four-cylinder compound design , differing in the compounding system used. By far the more numerous of the two were the von Borries locomotives. Instead of the de Glehn divided drive, these engines had HP and LP cylinder on each side cast as a single block and all four driving on the lead axle, but served by separate valves and valve gear. (See Locobase 6046 for the de Glehn variant, and 1263 for a description of a fuller description of the compounding layout.).

In French service, the 10 reparees ran under the Est's management and bore numbers 2701-2710.

Class S.9 (Locobase 1263)

Data from Albert H Bone, "Some Recent Designs of Locomotives for Service on Continental Railways", Cassier's Magazine, 1910, pp. 561-609 and Gustav Reder, The World of Steam Locomotives (1974, pl 278). See also Dgrr57, "Le type 69 (S 9) belge", 10 April 2010 post on Atlantic 221 - les stars de la Belle +poque thread at [], last accessed 4 October 2019; and Von Metzeltin,"Die neuen 2/5 gekuppelten Schnellzuglokomotiven der Preussischen Staatsbahn", Zeitschrift des Vereines Deutscher Ingenieure, Volume 53, No 17 (24 April 1909), pp. 641-648.

These Von Borries compounds had the typical wide firebox (indeed, the outline looks like a Belpaire), HP and LP cylinder on each side cast as a single block and driving on the lead axle, but served by separate valves and valve gear, and the slightly tapered boiler.

As Reder observes, trials against the smaller S6 showed higher coal consumption for the S9 when pulling trains between 224 and 502 tons. Above 500 tons, however, the S9 began to come into its own. Bone says that he "...more than once traveled behind these engines in rough weather with 52 axles = 445 tons behind the tender, on trains making non-stop runs of 158 miles at a booked average of 50 miles per hour, the engines easily managing this load and keeping good time."

In 1914, some engines were rebuilt with Knorr feedwater heaters and superheaters; see Locobase 12577.

A condition of the 1918 Armistice between the Central Powers and the Allies was an obligation to supply thousands of locomotives to countries whose railways were devastated by the war. Over 2,000 locomotives went to Belgium including 17 S9s. Designated Type 69, the engines proved well suited to fast passenger service out of Antwerp and Brussels. From the latter city, the 69 readily pulled Pullman express boat trains to Calais. Later duties included handling the International Brussels-Amsterdam trains.

Updated with various improvements, some of the class were fitted with smoke-lifters. Thirteen remained in service in 1946 and were redesignated 69.001-69.013. The class was retired in 1946-1948.

Class S.9 / BR 14 (Locobase 12577)

Data from [], last accessed on 10 May 2011. See also RAS Hennessey, Atlantic - The Well Beloved Engine (Stroud, Gloucestershire: Tempus Publishing, 2002), p 64,

These Von Borries compounds were originally delivered with saturated boilers in 1908; see Locobase 1263.

In 1914,engines rebuilt with Knorr feedwater heaters and superheaters were "reckoned to be the most economical of all Prussian express engines." 80 of them went into service in Elsass-Lothringen (Alace-Lorraine)

Even so, the DRG assigned numbers to only half the class and these were out of service by 1926. Roger Hennessey noted that the disposal of S9s was in line with a general Prussian/German antipathy toward the wheel arrangement. After an initial flush of delight with the S9's speed, its lack of adhesive weight so limited the design's usefulness that 27 had been retired by the time of the creation of the DRG in 1924.

Many of the retired S9s were used to fill out the war reparations roster of the Belgian Railways (17) and France's Est (4).