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Steam

This site is dedicated to Pennsylvania Railroad Steam Locomotives


These numbers, 0-4-0, 4-6-2, 2-10-0, 4-6-4-4 and many other like them define the wheel layout of the steam engines and therefore the type and classification for them. The type is the name used by the builders and are the same for all builders and railroad lines.

The classification system is unique to each railroad line. The only line we are talking about here is the PRR so we will say a given type is a given class, but please remember if you look at another line's engine it will have a different classification.

O.K. So just what do these numbers mean? Like I said above, it's really very simple, they define the wheel layout of the steam engines. The first number is how many leading (or pilot) wheels the engine has, and the last number is how many trailing wheels the engine has. The middle number or numbers are how many driving wheels it has.

For our example we will use the Pacific, a PRR class K, wheel arrangement 4-6-2.



There are 4 small leading wheels that help steer the engine around curves.
There are 6 large driver wheels.
And there are 2 trailing wheels that support the firebox.
Giving us a 4-6-2.
In the examples here we will use the standard symbols of 'o' for
the small wheels and 'O' for the big wheels or drivers.
The '/' is the front of the engine.

Wheel     layout          Type        PRR Class



0-4-0     /OO             Shifter         A

0-6-0     /OOO            Switcher        B

0-8-0     /OOOO           Switcher        C



4-4-0     /oo OO          American        D

4-4-2     /oo OO o        Atlantic        E

2-6-0     /o OOO          Mogul           F



4-6-0     /oo OOO         Ten Wheeler     G

2-8-0     /o OOOO         Consolidation   H

2-10-0    /o OOOOO        Decapod         I



2-10-4    /o OOOOO oo     Texas           J

4-6-2     /oo OOO o       Pacific         K

2-8-2     /o OOOO o       Mikado          L 



4-8-2     /oo OOOO o      Mountain        M

2-10-2    /o OOOOO o      Santa Fe        N

4-4-6-4   /oo OO OOO oo     **            Q



6-4-4-6   /ooo OO OO ooo    **            S1

6-8-6     /ooo OOOO ooo     **            S2

4-4-4-4   /oo OO OO oo      **            T



0-8-8-0   /OOOO OOOO        ***           CC

2-8-8-0   /o OOOO OOOO      ***           HC

2-8-8-2   /o OOOO OOOO o    ***           HH
** I do not know what these types are called, they are refereed to as 'Duplex' on some sites, except for the S2. If anyone knows the type of any of these (Q, S1, T, CC, or HC) please Send me an email I will give you credit on this page. If you have any references to cite I would appreciate you listing them.

*** Gerald Foley pointed out to me that the CC, HC and HH classes are not properly called duplex. They are all "articulated" (the two sets of driving wheels are in two different frames that pivot, to allow the engine to run around curves), and the CC and HH are "Mallet", named after the French inventor of the articulated compound locomotives of which they are examples. The HC1 is a simple articulated engine, not a Mallet nor a duplex.

Now, how about the signals? There are no red, yellow, and green lights on the PRR.

The description for signals below is very simplified and in the real world there are combinations of one type of signal used for many things. They use a ground level signal for track switches. They also place 2 signals, one above the other to indicate other things. This is beyond the scope of this site, which is to bring you pictures of PRR steam engines.

The railroad lines use at least 4 different types of signaling devices
1.) The semaphore which is a mechanical device, an arm with 3 positions.

a.) _ means STOP
b.) / means CAUTION
c.) | means ALL CLEAR


2.) The COLORED lights with 3 colors, just like the traffic lights on the streets.

a.) RED means STOP
b.) YELLOW means CAUTION
c.) GREEN means ALL CLEAR


3.) The POSITION light system with 3 lights for each signal. The lights are positioned like the semaphore.
This is the system used on the PRR.

STOP . . .. . . .

CAUTION . .

ALL CLEAR

4.) The COLOR POSITION light system with 3 colors, similar to the traffic lights on the streets except they use 2 lights for each signal. The lights are positioned like those in the description above with the center light removed.

a.) | RED means STOP
b.) / YELLOW means CAUTION
c.) _ GREEN means ALL CLEAR


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