Triplex Locomotives – 2-8-8-8-2 and 2-8-8-4-8-4

This is a Triples Locomotive:

Builder’s photo of the Virginian Xa, the sole 2-8-8-8-4 locomotive ever built

Why am I writing about Triplex Mocomotives when they had nothing to do with Mendocino Railroad History. Well, President Chuck Whitlock was at home cruising the Web watching vids of Train Mountain. Train Mountain is in Chiliquin north of Klamath Falls. Life Member Bill Shepherd owns a piece of land on the Train Mountain property and can run his 7.5 inch gauge equipment on the 37 miles (not an error) of track there. Chuck decided he was “obsessed” with finding out more about Triplex locomotives. I decided to help him out.

Only one 2-8-8-8-4T was ever built, a Mallet-type for the Virginian Railway in 1916. This is the one in the above photo. Built by Baldwin Locomotive Works, it became the only example of their class Xa, so named due to the experimental nature of the locomotive. Like the same railroad’s large articulated electrics and the Erie Railroad 2-8-8-8-2s, it was nicknamed “Triplex”.

The purpose of the Xa was to push heavy trains over steep inclines, requiring high tractive effort, but low speed, over short distances. The Xa worked on a difficult 14-mile section from Elmore to Clark’s Gap.

The Xa’s center set of cylinders received high-pressure steam, and the exhaust from these was fed to the two other sets of cylinders, which were valved for low pressure. The right cylinder exhausted into the front set of low pressure cylinders, and the left into the rear set; this is also why the high pressure cylinders have the same diameter as the low pressure ones, whereas most mallet locomotives have much smaller high pressure cylinders. The front set exhausted through the smokebox and the rear set exhausted first through a feedwater heater in the tender and then to the open air through a large pipe, which can be seen in the photo. Since only half of the exhaust steam exited through the smokebox, firebox draft (and thus boiler heating) was poor. Although the boiler was large (in line with contemporary two-cylinder and four-cylinder practice), six large cylinders demanded more steam than even such a boiler could supply. With all six cylinders operating at their full pressure (which could not be sustained for very long), the Xa produced huge amounts of tractive effort that may have been the highest of any steam locomotive before or since (160,000 pounds-force in compound mode, which was the largest tractive effort for any locomotive up to the time,1914-1916). The Xa is also considered the largest tank engine ever built since the tender had driving wheels as well and thus contributed to traction. The problem of variable adhesion on the Xa’s tender unit was not a serious one, since pusher locomotives had frequent opportunities to take on additional fuel and water.

The Xa was unable to sustain a speed greater than five miles an hour, since the six cylinders could easily consume more steam than the boiler could produce. The tender had a four-wheel truck at the rear to help guide the locomotive into curves when drifting back downhill after pushing a train over the hill.

The XA was sent back to Baldwin in 1920 and was rebuilt as two locomotives, a 2-8-8-0 and a 2-8-2. Unlike their progenitor which lasted only a few years in service, these two locomotives remained in service until 1953.

What about the 2-8-8-8-2 of which there were two:

Erie Railroad Triples # 1914

This engine (above) was ordered to work the difficult 14-mile section from Elmore to Clark’s Gap; only one was built. Although the boiler was bigger than that of the Erie triplex, there was still not enough steam. Another problem was steam leakage from the stuffing boxes of the tender cylinder, which obscured vision from the cab, and the machine was rebuilt without the powered tender.

You might think that an inherent problem with these engines- one that would have occurred to the designers- was that as the tender emptied, the adhesion of the rear driving wheels steadily decreased. However, Wiener states that since they were used for banking, there were frequent opportunities to replenish coal and water, and this was not a serious problem.

Virginia Railway Triplex # 1916




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