The reference for locomotives and railcars
Bavarian AA I
German Reichsbahn class 168
Germany | 1896 | only one produced

The AA I was a prototype used to test ways of saving coal and water by using a lift axle. It was based on the B XI, which was built from 1892 both as a conventional saturated simple locomotive and with a compound engine. The 4-4-0 wheel arrangement of the predecessor was modified by replacing the second coupled axle with a trailing axle. For this purpose, the lift axle with small wheels was used between the lead bogie and the first coupled axle, which was driven by a second engine with two smaller cylinders.

With this configuration, it was possible under most conditions to drive with only one driving axle, thus saving coal and water. The lift axle was raised using a pressure cylinder because running along with the additional engine being turned would have required more power. If more power or traction was needed, the lift axle was lowered and some of the steam was fed to its cylinders. Although the locomotive with this system was economical and reliable on a day-to-day basis, the complicated engine required more maintenance than with conventional steam locomotives. So it was decided to continue to procure the B XI.

After an accident in 1907, the AA I was converted into a 4-4-0 locomotive, making it look like its predecessor. In contrast to this, it received a superheater. With this powerplant, it was able to last the longest of all Bavarian 4-4-0 engines in service with the Reichsbahn and was therefore not retired until 1933 as road number 16 861.

Variantas builtrebuilt P 2/4
Axle config4-2-2-2 4-4-0 (American) 
Gauge4 ft 8 1/2 in (Standard gauge)
Dimensions and Weights
Length54 ft 4 3/8 in
Wheelbase24 ft 3 5/16 in
Fixed wheelbase8 ft 4 3/8 in8 ft 2 1/16 in
Service weight113,979 lbs
Adhesive weight61,729 lbs65,698 lbs
Axle load32,849 lbs
Water capacity3,830 us gal
Fuel capacity13,228 lbs (coal)
Power sourcesteam
Estimated power671 hp (500 kW)
Optimal speed50 mph26 mph
Top speed56 mph
Starting effort8,587 lbf16,771 lbf
with start valve10,304 lbf
Booster8,085 lbf
Power Plant
Driver diameter73.6 in
Boiler pressure188 psi
Expansion typecompoundsimple
Cylinderstwo, HP: 15 3/16 x 24 in
and LP: 24 x 24 in
two, 17 15/16 x 24 in
Grate area24.3 sq ft
Firebox area102.3 sq ft96.9 sq ft
Tube heating area1,257 sq ft1,018.3 sq ft
Evaporative heating area1,359.3 sq ft1,115.1 sq ft
Total heating area1,359.3 sq ft1,115.1 sq ft
Calculated Values
steam locomotive
lift axle
last changed: 01/2022

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