Kevin’s Komments 03/31/2021

Steam Engines

Most of us have a basic understanding of the USRA steam locomotive standards – When the USRA took over the railroads during WWI, they created standards for steam locomotives so that a number of locomotives could be produced and distributed to the railroads.  The reason was the deficit of steam locos caused by the war effort.  Railroads would order from the standard models, and the USRA would see that those models were distributed to the railroads as ordered/needed.  The engineers that designed the standards, used existing efficient models and practices, but then looked into the future and the direction steam power was going.  The net was that the standards were used long after the war.  And while most locomotive orders drifted away from the USRA standards by the late ‘20s, the last steam locos built (by the N&W) were USRA-like 0-8-0s.

USRA standards were developed for the switchers: 0-6-0 & 0-8-0, the road freight 2-8-2 & 2-10-2, the passenger pullers 4-6-2 & 4-8-2 (though many 4-8-2s ended up freight pullers), and the mallets 2-6-6-2 & 2-8-8-2.  Light and heavy versions existed for the 2-8-2, 2-10-2, 4-6-2, & 4-8-2.  The light versions kept weight less than 55,000 lbs per axle to accommodate railroads with lighter rail, while the heavy versions allowed up to 60,000 lbs per axle for heavier rail.  The least successful of the models were the mallets, though N&W’s Y class was based on the USRA 2-8-8-2.  The Mikados, 2-8-2s, were heavily produced and used for many years even after larger locos replaced them as prime freight movers.  The heavy Pacifics, 4-6-2s, had wheel diameters of 79” which allowed them to reach comfortable speeds above 80 mph.  The light Pacifics had wheel diameters of 73” which allowed them to reach comfortable speeds between 70 and 80 mph.  The other road engines had wheel diameters between 57” and 69” which allowed for comfortable speeds between 50 mph to 65 mph.  I called the speeds “comfortable” – the locos could reach higher speeds, but the beating of the rods became significantly stronger when over their comfortable speeds.  This heavy beating was not only felt through the train, but pounded the rails and the loco frame such that wear and damage could be significant.

Finally – pics!

First, the switchers. A few features – the headlight is at the top of the smokebox. The bell is between the front sand dome and the steam dome. There are two sand domes – front and back by the cab. Pilot is the step version.

The light and heavy Mikado have features common among the road engines: Headlight centered on the smokebox. Bell overhanging the top front of the smokebox. Spoked pilots. One sand dome. The road engines also had steps leading from the pilot to the sideboards.

The Santa Fe’s (light and heavy) carried the same “road loco” features with the pilot, bell, and headlight.  They also had the two sand domes, one just behind the steam dome.  Note a couple other feature common in all USRA designs:  the tapered stacks and rounded domes.  Also, the cabs carry a similar design with the rounded “barn” style roof and overhang, and simple rectangular windows.  The cabs all have footboards along the lower outside edge.

The light and heavy Pacifics have the same road loco features. These two picks present the fireman’s side and show the single cross-compound air pump mounted towards the middle below the sideboard. The trailing trucks are clearly shown in these picks – USRA designs had the earlier built-up trucks with spoked wheels. Later, the cast delta trailing trucks became common. Also note that the USRA designs were simple – no shrouding or covers even on the passenger locos. The turrets are open and visible along with the sanding valves on the sides of the sand dome.

The features of the light and heavy Mountains run similar to the Pacifics and all the road locos.

The two articulated mallet designs present a few changes from the typical road loco designs:  The headlight is mounted above the pilot.  The cross-compound air pump is mounted to the front center of the smokebox.  And, there are two sand domes  I was always a little curious about the power reverse on the articulated locos.  On the 2-6-6-2, you can see that there is a single power reverse over the rear set of drivers with a rod extending forward above the drivers to the front set.  (I guess I assumed there would be two power reverses – these picks show the USRA design with one and an extension rod.)  The 2-8-8-2 power reverse is a little more difficult to follow, but only one power reverse can be seen above the rear drivers.  The extension rod might be visible – not sure.

The modern steam locos were developed off of these designs.  Appliances that increased efficiency were added.  Railroads rebuilt or rearranged features based on their experiences and desires.  But, a lot of the basics of modern steam were first captured in these designs.  Here are some examples to compare to the pics above:
…a “light” Mikado – has a cast delta trailing truck but otherwise pretty close to the USRA:

This was either a USRA light Pacific, or built off-of the USRA design. The ACL added a second cross-compound air pump. Note the coal pusher on the tender. I believe coal pushers were part of the USRA design, but they don’t appear (or are not visible) on a lot of the modern steam.

This is a AT&SF “heavy” Pacific – similar to the USRA, but unique to AT&SF designs.

This is an N&W class Y3/Y3a mallet – a direct descendent of the USRA 2-8-8-2 design:

This is a PRR class N1 “Santa Fe”. I’m not sure how much the USRA design affected the PRR locos, but some of the original USRA Santa Fe’s were distributed to the PRR. The PRR shop rebuilt the fireboxes into the Belpaire version PRR preferred. Other modifications led to the N class seen here.

This is N&W #244, the last steam locomotive built for a US class 1 railroad. The design was a modernized version of the USRA 0-8-0 design.


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