PRR S2
Encyclopedia
The Pennsylvania Railroad
's class S2 was a steam turbine locomotive
. Only one prototype was built, #6200, delivered in 1944. The S2 was the sole example of the 6-8-6
wheel arrangement
in the Whyte notation
, featuring a six-wheel leading truck, eight driving wheel
s, and a six-wheel trailing truck. The S2 design used a direct-drive steam turbine
; the turbine was geared to the center pair of axles with the outer two axles connected by side rods. This had the advantage of simplicity. The disadvantage was that the turbine could not operate at optimal speeds over the locomotive's entire speed range. The S2 was the largest direct-drive turbine locomotive design ever built.
The locomotive was to be a 4-8-4
, but wartime restrictions on light steel alloys increased weight until six-wheel leading and trailing trucks were needed. Two turbines were fitted, one for forward travel and a smaller one for reversing at speeds up to 22 mph. A large boiler with a Belpaire firebox
and long combustion chamber
was fitted. The turbine exhaust was piped through a set of 4 nozzles in the smokebox
, providing an even draft for the fire and exiting through a unique quadruple stack. A Worthington-pattern feedwater heater
was fitted for increased efficiency. Twin air pumps for train braking were fitted below the running boards beside the smokebox front, and a large radiator assembly at the nose cooled the compressed air. The large 16-wheel tender was similar to that used on the PRR's other large passenger locomotives, the T1
and S1
.
In service the locomotive proved to be powerful and capable, with reserves of power at speed and reasonable fuel economy. The turbine drive was easy on the track and allowed more power to be delivered to the rails. The disadvantage was that, while economical at speed, the locomotive was highly uneconomical at lower speeds. The turbine used less steam than conventional locomotives above 30 mph; below that, the locomotive used excessive amounts of steam and fuel. The boiler normally operated at 310 PSI, but low speed steam usage could cause the pressure to drop as low as 85 PSI. The increased fuel usage at slow speeds also caused the firebox to run hotter, which sometimes caused stay bolts to break.
The locomotive's problems and the obvious advantages of the emerging diesel locomotive
technology ensured #6200 would never be duplicated. The locomotive was withdrawn from service in 1949 and scrapped in 1953.
Pennsylvania Railroad
The Pennsylvania Railroad was an American Class I railroad, founded in 1846. Commonly referred to as the "Pennsy", the PRR was headquartered in Philadelphia, Pennsylvania....
's class S2 was a steam turbine locomotive
Steam turbine locomotive
A steam turbine locomotive is a steam locomotive which transmits steam power to the wheels via a steam turbine. Numerous attempts at this type of locomotive were made, mostly without success...
. Only one prototype was built, #6200, delivered in 1944. The S2 was the sole example of the 6-8-6
6-8-6
In Whyte notation, a 6-8-6 is a steam locomotive with:* six unpowered leading wheels arranged into a three-axle leading truck,* eight powered driving wheels, and* six unpowered trailing wheels arranged into a three-axle trailing truck....
wheel arrangement
Wheel arrangement
In rail transport, a wheel arrangement is a system of classifying the way in which wheels are distributed beneath a locomotive.. Several notations exist to describe the wheel assemblies of a locomotive by type, position, and connections, with the adopted notations varying by country...
in the Whyte notation
Whyte notation
The Whyte notation for classifying steam locomotives by wheel arrangement was devised by Frederick Methvan Whyte and came into use in the early twentieth century encouraged by an editorial in American Engineer and Railroad Journal...
, featuring a six-wheel leading truck, eight driving wheel
Driving wheel
On a steam locomotive, a driving wheel is a powered wheel which is driven by the locomotive's pistons...
s, and a six-wheel trailing truck. The S2 design used a direct-drive steam turbine
Steam turbine
A steam turbine is a mechanical device that extracts thermal energy from pressurized steam, and converts it into rotary motion. Its modern manifestation was invented by Sir Charles Parsons in 1884....
; the turbine was geared to the center pair of axles with the outer two axles connected by side rods. This had the advantage of simplicity. The disadvantage was that the turbine could not operate at optimal speeds over the locomotive's entire speed range. The S2 was the largest direct-drive turbine locomotive design ever built.
The locomotive was to be a 4-8-4
4-8-4
Under the Whyte notation classification of steam locomotives, 4-8-4 represents the wheel arrangement of four leading wheels on two axles , eight powered and coupled driving wheels on four axles, and four trailing wheels on two axles .Other equivalent classifications are:UIC classification: 2D2...
, but wartime restrictions on light steel alloys increased weight until six-wheel leading and trailing trucks were needed. Two turbines were fitted, one for forward travel and a smaller one for reversing at speeds up to 22 mph. A large boiler with a Belpaire firebox
Belpaire firebox
The Belpaire firebox is a type of firebox used on steam locomotives. It was invented by Alfred Belpaire of Belgium. It has a greater surface area at the top of the firebox, improving heat transfer and steam production...
and long combustion chamber
Combustion chamber
A combustion chamber is the part of an engine in which fuel is burned.-Internal combustion engine:The hot gases produced by the combustion occupy a far greater volume than the original fuel, thus creating an increase in pressure within the limited volume of the chamber...
was fitted. The turbine exhaust was piped through a set of 4 nozzles in the smokebox
Smokebox
A smokebox is one of the major basic parts of a Steam locomotive exhaust system. Smoke and hot gases pass from the firebox through tubes where they pass heat to the surrounding water in the boiler. The smoke then enters the smokebox, and is exhausted to the atmosphere through the chimney .To assist...
, providing an even draft for the fire and exiting through a unique quadruple stack. A Worthington-pattern feedwater heater
Feedwater heater
A feedwater heater is a power plant component used to pre-heat water delivered to a steam generating boiler. Preheating the feedwater reduces the irreversibilities involved in steam generation and therefore improves the thermodynamic efficiency of the system...
was fitted for increased efficiency. Twin air pumps for train braking were fitted below the running boards beside the smokebox front, and a large radiator assembly at the nose cooled the compressed air. The large 16-wheel tender was similar to that used on the PRR's other large passenger locomotives, the T1
PRR T1
The Pennsylvania Railroad's 52 T1 class duplex-drive 4-4-4-4 steam locomotives, introduced in 1942 and 1946 , were their last-built steam locomotives and their most controversial. They were ambitious, technologically sophisticated, powerful, fast, and uniquely streamlined by Raymond Loewy...
and S1
PRR S1
The PRR S1 class steam locomotive was an experimental locomotive that was the largest rigid frame passenger locomotive ever built. The streamlined Art Deco styled shell of the locomotive was designed by Raymond Loewy....
.
In service the locomotive proved to be powerful and capable, with reserves of power at speed and reasonable fuel economy. The turbine drive was easy on the track and allowed more power to be delivered to the rails. The disadvantage was that, while economical at speed, the locomotive was highly uneconomical at lower speeds. The turbine used less steam than conventional locomotives above 30 mph; below that, the locomotive used excessive amounts of steam and fuel. The boiler normally operated at 310 PSI, but low speed steam usage could cause the pressure to drop as low as 85 PSI. The increased fuel usage at slow speeds also caused the firebox to run hotter, which sometimes caused stay bolts to break.
The locomotive's problems and the obvious advantages of the emerging diesel locomotive
Diesel locomotive
A diesel locomotive is a type of railroad locomotive in which the prime mover is a diesel engine, a reciprocating engine operating on the Diesel cycle as invented by Dr. Rudolf Diesel...
technology ensured #6200 would never be duplicated. The locomotive was withdrawn from service in 1949 and scrapped in 1953.