"Triplex" Steam Locomotive: Specs, History, Photos
Last revised: October 6, 2026
By: Adam Burns
The Erie Railroad’s Triplex was a Mallet compound with three engines, a unique 2-8-8-8-2 wheel arrangement: a leading truck, three sets of eight drivers, and a trailing truck under the tender. Baldwin built three, class P-1. The first, works 41308, left in August 1914 as number 2603 and was later 5014. The railroad painted the name Matt H. Shay on that engine, for an Erie engineer. The other two, works 43350 and 43351, followed in May 1916 as 2604 and 2605, later 5015 and 5016.
George R. Henderson of Baldwin designed them as helper engines. On the Erie they pushed at Gulf Summit, the grade also called Susquehanna Hill, between Deposit, New York, and Susquehanna, Pennsylvania. Six cylinders of the same size emptied the boiler once speed rose much above 10 miles an hour. The steam roster retires the class in 1929–1933.
One more Triplex was built. The Virginian took a single 2-8-8-8-4, class XA, number 700, Baldwin works 44448, in November 1916. Baldwin also drew a 2-8-8-8-2 for the Denver & Rio Grande Western in the same season as the Matt H. Shay’s first runs. That engine stayed on paper. Four Triplexes were built. All four were scrapped.
A crowd around Erie 2-8-8-8-2 No. 5014, the Matt H. Shay, at the yard in Binghamton, New York, circa 1914. Baldwin built the engine in 1914. The railroad named it for Matt H. Shay, an Erie engineer. Photographer unknown.
On this page: At a glance · Three engines, one boiler · The 1930 class card · Susquehanna Hill · Three locomotives · Virginian 700 · A Rio Grande drawing
At a glance
| Item | Detail |
|---|---|
| Railroad | Erie Railroad. Class P-1. Three engines |
| Whyte | 2-8-8-8-2. Three engine sets. The last set sits under the tender |
| Builder | Baldwin. George R. Henderson’s design. Baker valve gear |
| Numbers | 2603, later 5014, the Matt H. Shay, August 1914, works 41308. 2604 and 2605, later 5015 and 5016, May 1916, works 43350 and 43351 |
| Cylinders | High pressure, two, 36 × 32 in, in the middle. Low pressure, four, 36 × 32 in, one pair ahead and one pair under the tender. Compound at all times |
| Drivers | 63 in. Boiler 210 psi |
| Tractive effort | 176,256 lb calculated, 1930 Locomotive Cyclopedia. Factor of adhesion 4.32 on that figure. 160,000 lb compound, in Douglas Self’s compilation |
| Weight | On drivers, 761,600 lb. Engine, 853,050 lb. Tender, loaded, 316,700 lb. Engine and tender, 1,169,750 lb |
| Grate | 90 sq ft as delivered on the first engine. 121.50 sq ft on the 1930 class card, the grate of the second and third |
| Tender | Water 11,600 gallons. Coal 16 tons. The tender tank rides on the third engine |
| Service | Pusher, Gulf Summit / Susquehanna Hill, Deposit, New York, to Susquehanna, Pennsylvania |
| Retired | 1929–1933. Number 5014 was scrapped in October 1929. None preserved |
| The other Triplex | Virginian class XA, 2-8-8-8-4 No. 700, November 1916. Taken apart at Baldwin in 1921. The parts became AF 610 and MD 410 |
Erie dimensions are the 1930 Locomotive Cyclopedia class card, as compiled by Steve Llanso, Locobase 3300, with Baldwin specifications in the DeGolyer Library volumes he cites. The 160,000-pound compound figure is Douglas Self’s. Retirement years follow the Erie steam roster. Information compiled October 6, 2026.
Three engines, one boiler
A Mallet already has two engines under one boiler. The front engine is hinged. The rear engine is fixed to the boiler, and the high-pressure cylinders sit ahead of it and exhaust forward into the low-pressure pair. Henderson added a third engine, under the tender, and kept every cylinder the same size. The two high-pressure cylinders are the middle pair, 36 by 32 inches. They exhaust into four low-pressure cylinders, also 36 by 32 inches, two under the smokebox and two at the back of the tender. The front low-pressure pair exhausts up the stack, which is what keeps a draft on the fire. The rear pair exhausts through a feedwater heater of 437 square feet and up a narrow pipe at the rear of the tank.
The third engine is why the wheel arrangement is a 2-8-8-8-2. Twelve driving axles carry the adhesive weight, and the coal and the water are part of that weight because they sit on the last eight drivers. A two-wheel truck trails behind the tank. Valve gear is Baker. The engines worked compound. George H. Drury’s note, as Steve Llanso quotes it, is that they were never simpled, even for starting, because two or three revolutions of the drivers would have exhausted the boiler.
The boiler that had to supply those six cylinders was pressed to 210 pounds. Drivers are 63 inches. As delivered, the grate measured 90 square feet. Llanso calculates that grate against the cylinder demand and calls the combination impossible. The second and third engines were given a larger grate by taking out the Gaines brick wall in the firebox. Arch-tube surface came down with that change, from 88 square feet to 74. The 1930 class card records the enlarged grate as 121.50 square feet. On the first layout the firebox heating surface included 108 square feet of combustion chamber and the 88 square feet of arch tubes.
A Baldwin builder's photograph of Erie 2-8-8-8-2 No. 5016. This locomotive was one of the two engines of May 1916, works 43350 and 43351, originally 2605.
The 1930 class card
The figures below are the class card in the 1930 Locomotive Cyclopedia, the card Locobase 3300 transcribes for Erie P-1. One column covers the three engines as the cyclopedia listed them. The grate on that card is the enlarged grate. The first engine was built with 90 square feet. The cyclopedia’s tractive effort is a calculated figure. Self’s figure is the compound rating he compiles for the Matt H. Shay. The factor of adhesion 4.32 divides the 761,600 pounds on the drivers by the calculated 176,256.
| Specification | 1930 Locomotive Cyclopedia, class P-1 |
|---|---|
| Class / Whyte | P-1. 2-8-8-8-2. Three engines |
| Road numbers | 5014–5016, formerly 2603–2605 |
| Builder | Baldwin. 41308 in August 1914. 43350 and 43351 in May 1916 |
| Valve gear | Baker |
| Driver wheelbase | 49 ft 6 in |
| Engine wheelbase | 71 ft 6 in |
| Engine and tender wheelbase | 91 ft |
| Maximum axle load | 70,100 lb |
| Weight on drivers | 761,600 lb |
| Engine weight | 853,050 lb |
| Tender, loaded | 316,700 lb. Water 11,600 gallons. Coal 16 tons |
| Engine and tender | 1,169,750 lb |
| Drivers / boiler | 63 in. 210 psi |
| Cylinders | Two high-pressure, 36 × 32 in. Four low-pressure, 36 × 32 in |
| Tractive effort, calculated | 176,256 lb. Factor of adhesion 4.32 |
| Tractive effort, compound | 160,000 lb, in Douglas Self’s compilation of the Matt H. Shay |
| Tubes and flues | 326 tubes, 2¼ in. 53 flues, 5½ in. Length 24 ft |
| Heating surface | Firebox 468 sq ft. Evaporative 6,886. Superheater 1,584. Combined 8,470 sq ft |
| Grate | 121.50 sq ft on this card. 90 sq ft as delivered on the first engine |
| Rear exhaust | Feedwater heater, 437 sq ft, then a pipe at the rear of the tank |
Engine weight and the loaded tender add to the 1,169,750 pounds. Evaporative surface and superheater add to the 8,470. Twelve driving axles and a loaded tender of only 16 tons of coal tell the same story as the fireman’s complaint below. The adhesive weight was enormous. The grate, even after it was enlarged, was the grate of a large conventional engine, asked to steam six cylinders.
Susquehanna Hill
The grade these engines were built for is the same hill that had already produced Erie’s earlier articulateds. In 1907 Schenectady delivered three Camelback 0-8-8-0s, class L-1, for pusher service between Deposit and Susquehanna. A shop-built 2-6-8-0 followed in 1910. Both experiments are on the steam roster. The Triplex was the next attempt to put one crew on the helper job at Gulf Summit, less than thirty miles east of Binghamton and close to the Pennsylvania line.
The first engine was said to be capable of 640 cars. What Comstock recorded in 1971, and what Llanso repeats, is a shorter run and a harder stop. The Matt H. Shay did start a train of 250 coal cars. The run lasted 17 miles. The force of the pull then snatched one from a coal car and stopped the train. Couplers, draft gear, and car frames of the mid-1910s were the limit, so the three engines stayed in pusher service. Llanso’s summary is that they were useful pushers on Susquehanna Hill into the late 1920s.
Two other limits sat in the machine itself. Above about 10 miles an hour the six cylinders used steam faster than the boiler could make it. And the factor of adhesion on the tender engine fell as the coal and the water were burned, because that fuel was the weight on the last set of drivers. An Erie fireman, Andrew Goobeck, put the draft problem in one sentence. Writing in Railroad Magazine in October 1942, in the passage Comstock quotes, he said the best place for anybody to cool off on a summer day was behind the firedoor.
The Berkshires changed the helper pool. Class S 2-8-4s began arriving in 1927, and the 2-10-2s they released from other work could take the pusher assignments. The Triplexes came off that job in those years. Roster retirement is a later pair of dates. The steam roster’s years for P-1 are 1929–1933. Number 5014 was scrapped in October 1929. The Erie & Wyoming Valley shops at Dunmore, Pennsylvania, had given 5016 a minor overhaul in 1920, while the class was still in helper service. None of the three was saved.
Erie 2-8-8-8-2 No. 5016. The number is on the cab and ERIE is lettered on the tender. The third engine is under the tank. Photographer unknown.
Three locomotives
| Later no. | Original no. | Built | Works | Retired | Notes |
|---|---|---|---|---|---|
| 5014 | 2603 | August 1914 | 41308 | Scrapped October 1929 | The Matt H. Shay, for some years. First of the class. Grate 90 sq ft as delivered |
| 5015 | 2604 | May 1916 | 43350 or 43351 | 1929–1933 | Enlarged grate. One of the two May 1916 works numbers |
| 5016 | 2605 | May 1916 | 43350 or 43351 | 1929–1933 | The other May 1916 works number. Minor overhaul at Dunmore, 1920. The Baldwin builder photograph shows this number on the cab |
The class count is three, which is the count on the steam roster: Baldwin, 1914 and 1916, retired 1929–1933, with the name Matt H. Shay on 5014. The works numbers of the 1916 pair are 43350 and 43351, one number to each engine.
Virginian 700
Virginian 2-8-8-8-4 No. 700, circa 1916, Baldwin. Class XA. The number is on the tender tank, and a four-wheel truck trails under the tank for drifting back down the grade. Baldwin works 44448, November 1916.
The Virginian was a coal road from the West Virginia mines to tidewater, and its helper grade was Elmore to Clark’s Gap. Baldwin’s specification, as Llanso summarizes it from the DeGolyer papers and from the March 1917 descriptions in Railway and Locomotive Engineering and Engineering News, asked number 700 to drag 2,580 tons over that run. Fourteen miles, of which 12 miles ascended at 2.07 percent and wound through ten 12-degree curves. Four-fifths of the load, 2,064 tons, was to go up at 10 miles an hour.
The engine built for that specification was class XA, the experimental engine of its series, a 2-8-8-8-4. Works number 44448, November 1916. The cylinders are two inches smaller than the Erie engines, 34 by 32 inches, two high-pressure and four low-pressure. The boiler is a little larger. Drivers are 56 inches, pressure on the class card is 222 pounds, and the calculated tractive effort is 186,975 pounds, with a factor of adhesion of 3.88. Weight on the drivers is 725,475 pounds. The engine weighs 842,310 pounds. Water is 13,000 gallons and coal is 12 tons. The grate is 107.60 square feet. Combined heating surface on the card is 10,179 square feet. A four-wheel truck under the back of the tender was there so the engine could track when it drifted back down the hill. Baldwin people stayed with it in service.
| Specification | Virginian XA 700, Locobase 3301 |
|---|---|
| Whyte / class | 2-8-8-8-4. Class XA. One engine, number 700 |
| Builder | Baldwin works 44448, November 1916. Baker valve gear |
| Wheelbases | Drivers 45.75 ft. Engine 67.58 ft. Engine and tender 91.25 ft |
| Weight | Maximum axle load 62,000 lb. On drivers 725,475 lb. Engine 842,310 lb |
| Tender capacity | Water 13,000 gallons. Coal 12 tons |
| Drivers / boiler | 56 in. 222 psi |
| Cylinders | Two high-pressure, 34 × 32 in. Four low-pressure, 34 × 32 in |
| Tractive effort | 186,975 lb calculated. Factor of adhesion 3.88 |
| Tubes and flues | 365 tubes, 2¼ in. 65 flues, 5½ in. Length 25 ft |
| Heating surface | Firebox 431 sq ft. Evaporative 8,120. Superheater 2,059. Combined 10,179 sq ft. Grate 107.60 sq ft |
Drury’s comparison, again as Llanso quotes the 1993 text, is that 700 was slower than the Erie engines and ran out of steam faster. One tunnel on its road had four inches of clearance. His conclusion is that it never made a successful trip. The older Triplex account on the same site puts the steaming limit near 5 miles an hour, against about 10 on the Erie.
In 1921 Baldwin took the locomotive apart and sent two new engines back. The boiler went onto a 2-8-8-0, class AF, number 610, works 55100, September 1921. The cylinders of that Mallet match the Virginian’s 1913 ADs, and the tube layout remained the Triplex boiler. In November 1942 the AF was given a trailing truck and became a 2-8-8-2. It ran until 1953. The tender engine became a 2-8-2, class MD, number 410, rebuilt in December 1921 and the only locomotive in that class. It also ran until 1953. Number 700 itself ended in the 1921 split.
A Rio Grande drawing
In the same year the Matt H. Shay went to work, Baldwin prepared a 2-8-8-8-2 proposal for the Denver & Rio Grande Western. Locobase 6823 transcribes the drawing, which a later Rio Grande diagram book still carried. The cylinders are 34 by 32 inches, two inches smaller than the Erie engines. The grate was held to 80 square feet by a Gaines wall, the same idea the Erie then removed when 90 square feet proved too small. Valve gear on the proposal is Walschaert. The Erie’s experience ended the interest, and the proposal stayed a drawing. Henderson also laid out a four-engine machine, a 2-8-8-8-8-2, and that stayed a drawing too.
Related reading on American-Rails.com
- Erie Railroad · Erie steam roster · Berkshire type
- Mallet locomotives · Camelbacks · Feedwater heaters · Baldwin Locomotive Works
- Virginian Railway · Denver & Rio Grande Western
Sources
- Llanso, Steve. Locobase 3300, on steamlocomotive.com. Erie class P-1. Data from the 1930 Locomotive Cyclopedia, and from Baldwin specifications in the DeGolyer Library, Volume 50, pp. 184+, and Volume 55, pp. 125+. Works 41308 in August 1914, and 43350 and 43351 in May 1916. Baker valve gear. The compound arrangement, the 437-square-foot feedwater heater on the rear exhaust, the 90-square-foot grate as delivered, and the enlarged grate on the second and third engines, with arch tubes reduced from 88 to 74 square feet. The class-card dimensions in the table above, including calculated tractive effort of 176,256 pounds and a factor of adhesion of 4.32. Drury’s 1993 note that the engines were never simpled, even for starting. Comstock (1971), quoting Andrew Goobeck, Railroad Magazine, October 1942, on the firedoor, and the Matt H. Shay’s start with 250 coal cars, ended after 17 miles.
- Self, Douglas. "The Triplex Locomotive," on douglas-self.com. The compound tractive effort of 160,000 pounds compiled there for the Matt H. Shay. Dimensions in the tables are the 1930 cyclopedia card.
- Drury, George H. Guide to North American Steam Locomotives, revised edition, as used for the class line on this site’s Erie steam roster: P-1, numbers 5014–5016, three engines, Baldwin, built 1914 and 1916, retired 1929–1933. The same roster records the Matt H. Shay name on 5014, the 1920 minor overhaul of 5016 at Dunmore, and the 1927 arrival of the S-class Berkshires. Llanso’s quotations of Drury’s 1993 text cover the compounding sentence and, for the Virginian, the comparison with the Erie engines, the four inches of tunnel clearance, and the line that 700 never made a successful trip.
- SteamLocomotive.com, the Triplex overview beside the Locobase entries. Original numbers 2603–2605, soon renumbered 5014–5016. Pusher service on Gulf Summit, or Susquehanna Hill, near Deposit, New York. Steaming limited to about 10 miles an hour on the Erie and about 5 on the Virginian. The 640-car claim, stated there as something said of the first engine. Number 5014 scrapped in October 1929. Build years in this account are the Baldwin works dates, August 1914 and May 1916.
- Llanso, Steve. Locobase 3301. Virginian class XA, number 700, works 44448, November 1916. DeGolyer, Volume 55, pp. 187+. Railway and Locomotive Engineering, Volume 30, No. 3 (March 1917), pp. 73–76. Engineering News, Volume 77, No. 11 (March 15, 1917), pp. 417–418. The class card in the Virginian table, the 2.07 percent specification from Elmore to Clark’s Gap, and the split of the engine into a 2-8-8-0 and a 2-8-2.
- Llanso, Steve. Locobase 3566. Virginian class AF, number 610, a 2-8-8-0, works 55100, September 1921, using the Triplex boiler. A trailing truck added in November 1942 made it a 2-8-8-2. In service until 1953. Locobase 7486, and the Virginian Mikado roster on the same site: class MD, number 410, a 2-8-2 rebuilt in December 1921 from the tender unit of 700, the only engine of that class, in service until 1953.
- Llanso, Steve. Locobase 6823. Baldwin’s unbuilt 2-8-8-8-2 proposal for the Denver & Rio Grande Western, drawn the same year as the Matt H. Shay’s first runs. Cylinders 34 by 32 inches. Grate held to 80 square feet by a Gaines wall. Walschaert valve gear. The diagram survived in a Rio Grande diagram book, D&RGW 12, 1937, Folio 10.
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Kentucky railroad museums—the Kentucky Railway Museum, Bowling Green’s L&N depot, Paducah, Versailles, and Covington. Confirm hours on each site. -
Kansas Railroad Museums (2026): A Complete Guide
Oct 07, 26 11:26 AM
Kansas railroad museums—Santa Fe 3768 at Wichita, Santa Fe 132 in Topeka, the Great Overland Station, and Abilene. Confirm hours on each site. -
Cincinnati, New Orleans and Texas Pacific Diesel Roster (All-Time)
Oct 07, 26 10:38 AM
All-time diesel roster of Southern locomotives lettered for the Cincinnati, New Orleans and Texas Pacific. Serials, order numbers, and builder dates. -
Cincinnati, New Orleans and Texas Pacific Railway
Oct 07, 26 10:31 AM
Cincinnati, New Orleans and Texas Pacific Railway, incorporated September 8, 1881, to lease Cincinnati’s railroad to Chattanooga. Queen and Crescent route, Rathole, and the 2024 sale to Norfolk Southe… -
Indiana Railroad Museums (2026): A Complete Guide
Oct 07, 26 12:26 AM
Indiana railroad museums—Nickel Plate 765, Elkhart’s New York Central collection, French Lick, Linden’s junction depot, and Haley Tower. Confirm hours on each site. -
"Triplex" Steam Locomotive: Specs, History, Photos
Oct 06, 26 11:52 PM
Erie class P-1 Triplex 2-8-8-8-2s. Three Baldwin compounds, 2603–2605, later 5014–5016, built 1914 and 1916. Matt H. Shay, the 1930 class card, and Virginian XA 700. -
Illinois Railroad Museums (2026): A Complete Guide
Oct 06, 26 11:47 PM
Illinois railroad museums—the Illinois Railway Museum, Monticello, the Pioneer Zephyr, Galesburg’s Burlington 3006, and the depots. Confirm hours on each site.
Impact
The Triplex locomotive was a natural progression of steam technology as builders and railroads sought to develop more powerful designs to handle increasingly larger and heavier trains.
Unfortunately, experimental designs like the Triplex, steam turbines, and even Duplexes proved to be relatively unsatisfactory in service. Nevertheless, they were fascinating concepts aimed at reducing operating costs.
In retrospect, the Triplexes time in service would have been relatively short lived, even had they been successful. The age of the diesel-electric was just around the corner and Electro-Motive unveiled its FT in 1939.
In addition, Erie had been experimenting with early diesel switchers by the mid-1920s and acquired its first FTs in 1944. For a railroad constantly plagued with debt and bankruptcy it quickly retired its steam fleet and was fully dieselized by the mid-1950s.