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Transport history notes >
Mallet locomotives N&W USA.
This form of articulated locomotive was well developed in the USA. The Norfolk & Western Railway Co produced two variations on this theme, the 2-6-6-4 & the 2-8-8-2 known as “A” & “Y” class. The main frame of the loco’ supported the boiler and the rear half of the motive power ( the 6-4 or the 8-2 bit ! )This was supplied with 270-300 psi steam pressure and drove the rear traction six or eight wheels. The steam was then piped forward to the LP cylinders after exhausting from the rear HP cylinders, the “Y” classes LP cylinders then used the remaining steam pressure ( 70-90 PSI) in 39 inch diameter cylinders, so this was a true Mallet compound locomotive. The “A “ class used 4 X 30 inch cylinders, all HP @ 270 PSI, so this class was a “simple” layout and used only full boiler pressure on all cylinders.
“Y” class were also produced as “ simple” locomotives having 300 psi boiler pressure. The front drivers were articulating and pivoted under the boiler to allow this long machine to negotiate curves. The steam supply also needed to “ swivel “ so a jointed steam pipe was needed and could be the “ achilles heal “ of the design . These locomotives were very powerful and would produce 4500-5000 HP. Used on 10,000 ton coal trains in Virginia these giants were some of the best Mallet type locomotives ever produced. See a small clip of them at work ! Click on the icon below.
The locomotive below is “Y” class
This machine had an overall weight of 480 tons (US)
That is three times and more the size of any UK freight locomotive. (9F)
In the 4000-5000HP class the “Blue mountains “would echo the sound of their sirens.
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