Pennsylvania Railroad T1 technology
The Pennsylvania Railroad had a reputation for blazing its own path, setting a standard different from the rest of the railroad community. Such is the case with its T1 class 4-4-4-4 duplex locomotives. In spring 1942, prototypes Nos. 6110 and 6111 were quietly rolled from the Baldwin Locomotive Works. The Pennsy liked what they saw and from 1945 to 1946 built a fleet of 50 additional T1s — 25 erected by Baldwin, 25 came from the railroad’s shops at Altoona, Pa.
The same trail-blazing spirit exists in the contemporary T1 Trust, which is currently working to build a new T1 from the rails up. Starting in 2014, by casting a keystone-shaped number plate bearing the new locomotive’s identity — 5550 — it began fabricating the 51st T1 (not counting the prototypes). The group has conducted extensive research, including gathering almost a complete set of the original blueprints, in an effort to create an authentic rendition more than half a century after all the originals were scrapped.
What’s old is new again
T1 No. 5550, due to be completed by 2030, will be a near reproduction of No. 5500, as it appeared in 1947. There will be some technological differences between the originals and the new edition. The first T1s burned coal. No. 5550 will run on oil. The originals had riveted boilers and cast frames and cylinders. The new T1 will have a welded boiler, frame, and cylinders. The steam distribution system and poppet valves — we’ll talk about these in a moment — will be the later Franklin B2 type, as opposed to the less-successful type A used originally.
Differences aside, the T1 Trust is working to faithfully build a new, yet original, locomotive. Jason Johnson, Trust general manager, talked about the technical differences, “If the [Pennsylvania Railroad] is building steam locomotives today, this is how they’d do it. You would not rivet. A rivet gives you another point of failure and a place for a leak to occur. When all of our welds are done, they are radiographed. They are 100% perfect welds every time.”
The group has also researched the metallurgy used by the Pennsy for cast parts and replicated the formulas for use in new castings. They are working to keep the weight of the No. 5550 within 2% of the original T1s. Speaking of the new frame, which is currently in production, Johnson says, “The center of gravity is in the exact same location on both frames, and both frames are within a thousand pounds of each other.”
Under the hood
The T1 was a sleek, shark-nosed, streamlined affair with a stylish outer skin fashioned by the artistic mind of industrial designer Raymond Loewy. The class was among a number of other Pennsy rail vehicles to receive a Loewy dressing. The GG1 electric, K4 Pacific, duplex 6-4-4-6 S1, 4-6-4-4 Q1 and the 1939 Broadway Limited all bore Loewy industrial styling.
In the case of the T1, as with the other U.S. locomotives, the artistic skin merely shielded the technology at work beneath. Despite World War II restrictions, it was becoming clear that diesels would power U.S. trains following the conflict. The Pennsylvania Railroad had different thoughts, believing steam — if the technology could be pushed further — would yield more efficient power than a diesel locomotive. The railroad was both right and wrong.
Go big or go bigger
The T1s were monster locomotives and a study in the best technology of their time. Measuring 122 feet 93/4 inches over the couplers, they sported a 107-foot wheelbase. (The Union Pacific Big Boy is 132 feet 97/8 inches long.) The T1s were designed for hustling passenger trains at more than 70 mph. The Pennsy’s idea was to couple a T1 onto a westbound train at Harrisburg, Pa., have it run to Chicago with one coal stop at Millbrook, Ohio, 385 miles west of Harrisburg, and do so while meeting or beating established schedules.
evident in this builder’s photo. The T1s measured 122 feet 93/4 inches over the couplers — only 10 feet shorter than the Union Pacific Big Boys. Note the water scoop between the tender trucks. Three photos, Baldwin Locomotive Works
The T1 locomotive weighed in at 502,200 pounds, the tender at 442,500 pounds, totaling 944,700 pounds. These figures included 62,000 pounds of coal and 19,200 gallons of water in the tender.
Think of the 4-4-4-4 wheel arrangement as an uncoupled 4-8-4. The running gear was smaller — four 10-foot main rods versus two 30-footers — and lighter, resulting in less total weight, shorter cylinder stroke, and less wear and tear on parts. All rods and reciprocating parts on a T1 weigh 9,152 pounds, while a Pennsylvania Railroad study found the same parts on an average 4-8-4 tallied 11,291 pounds.
The Pennsy tested a T1 at its plant in Altoona against one of its M1a 4-8-2 Mountain-type locomotives. The M1a and T1 had the same weight on the driving wheels. The T1 generated 6,552 hp, which was 46% more than the M1a. That is also more than the 6,300 hp put forth by the Union Pacific Big Boys. The T1’s goal was to haul 800 tons of passenger train at 100 mph on level tangent track, requiring 2,838 drawbar horsepower at 38 mph. The T1 generated 6,000 drawbar hp above 55 mph, giving the railroad the confidence that a T1 could out perform a four-unit, 5,400-hp EMD FT diesel at any speed over 26 mph.
Aluminum was used to fabricate many T1 parts saving additional weight. The streamlined jacket, hip castings, sand boxes, cab, decks, steps, skirting and running boards were all aluminum, deducting 17,000 pounds from the total weight.
Not the same old valve
One of the most significant features of the T1s was the use of poppet valves instead of the normal spool-shaped, sliding valve system. With a spool-shaped valve, steam is always simultaneously being exhausted from and admitted into the cylinders. As the valve slides back and forth, the percentage of motion devoted to admitting steam and exhausting it will change continuously.
Such valve actions use considerable horsepower. “The typical Baker or Walschaerts valve gear uses between 200 and 300 hp that the engine is producing just to operate the valves and associated gear,” says Johnson.
For the Pennsy’s 50-locomotive T1 fleet, the railroad insisted on using the Franklin steam distribution system with oscillating cams and poppet valves. Think of a device similar to the valves in an automobile engine. As a cam shaft rotates, either the intake valve or the exhaust valve is opened. Steam is admitted to the cylinder and the valve is closed. The process repeats for the exhaust. A dedicated exhaust valve is opened, allowing steam to escape the cylinder.
The poppet valve, with its on-or-off action, dramatically improves steam-usage efficiency. In the spool valve, steam has not fully expanded by the time the valve moves to begin the exhaust portion of the cycle. With a poppet valve, steam is allowed to expand more fully before the exhaust port opens — a port that is larger than the intake port to accommodate the expanded steam. On the Franklin type-A system intake valves measured 5 inches across. The exhaust valves were 6 inches. Two intake and two exhaust valves were placed on the front and back of each cylinder, equipping the T1s with 32 total valves.
The valve system relates to how fast a locomotive can actually travel, Johnson says. On paper, the math indicates an 80-inch driver diameter should move the locomotive at speeds up to 130 mph. “At that speed … those 80-inch drivers would be running at 400 [to] 450 rpms. This is the why a poppet valve over a piston valve is the key at high speeds. On an engine like the [Union Pacific No.] 844, or pick your big engine of choice … they all have the same problem, in that the intake steam has to exit through the same exact size porting when it leaves and goes to exhaust.
“Steam expands 1,600 times when it hits the atmosphere. When it hits that piston, the steam all of a sudden expands its volume up to 1,600 times bigger than when it came in. Now it has to go back out through the same size hole that it came in. That causes back pressure. The piston can’t, at 400 rpm, get the expanded steam out fast enough to make speeds of a hundred miles an hour.”
Don’t go breaking my valves
The poppet valves patented in the United States and used on the T1s came from Franklin Railway Supply, a company with ties to Lima Locomotive Works and not Baldwin. William Woodard, Lima’s design chief, assembled a team under the direction of Julius Kirchhof, an Austrian engineer, to develop a valve set capable of operating at 500 rpm or 120 mph with 80-inch drivers. The team was successful with the system being installed on the T1s. Franklin guaranteed the poppet valves would run at a sustained 100 mph, with short-duration speeds up to 125 mph.
Valve breakage became a problem on the T1s. Franklin’s engineers could not determine the cause, but realized the random breaks were generally occurring on the track between Crestline, Ohio, and Fort Wayne, Ind., where 100 mph was the top speed. Kirchhof sent a Franklin staffer “undercover” to ride trains in this area for a month. The collected data showed that Pennsy engineers routinely made up time on this stretch, pushing the T1s to more than 125 mph. On two occasions, shorter six- and seven-car trains reached 135 to 142 mph and held that speed for several miles.
Kirchhof did not share the findings with the Pennsy, but rather attempted to re-engineer the valves. Despite numerous approaches, it was determined that regardless of material, the valves were prone to breakage above 100 mph.
Don’t slip
From the beginning with Nos. 6110 and 6111, driver slippage was a notable negative trait of the T1s. When the pilot truck and front driving wheels passed over an irregularity in the rails, they would slip and then catch. The rear drivers would then encounter the same spot and slip as well. In some cases, the imbalance created would cause the front drivers to slip again. Slipping at slower speeds was disconcerting, however, the T1s would also slip at higher speeds. Driver slip at 80 mph caused excessive vibration and lurched the locomotive along the rails. To control the situation, the engineer had to quickly cut power, then slowly reopen the throttle until the wheels caught, hoping not to lose too much speed in the process. Some T1s received sanding devices to help control slip at speeds up to 25 mph. It was also noted that the wheel slippage increased on the 50 production T1s. This was attributed to train handling. The prototypes were generally run by senior crews, whereas the production units ran with crews called from the board.
Young and done
The T1s had a number of qualities that brought about their early demise, with the class being scrapped between 1953 and 1956. Loewy’s streamlined shroud caused plenty of access headaches for maintenance crews. Although the decoration could be and was trimmed back, this was a minor detrimental reason. The wheel slip was eventually solved; however, this was a situation of too little, too late. The average engineer did not acquire the finesse to operate a T1. Wheel slippage is bad enough at low speeds, but a slip at 80 mph was a scary proposition. The poppet valve breakage posed a considerable concern despite re-engineering efforts. The real death knell for the T1s was the 1948 announcement by Martin W. Clement, Pennsylvania Railroad president: “By May of this year, we expect all of our important east-west through passenger trains will be diesel powered west of Harrisburg.”
By weight, the T1 Trust is more than half finished with No. 5550. When done, the plan is to make a run at the world speed record for steam locomotives established by London & North Eastern Railway A4 No. 4468 — Mallard — on July 3, 1938. The 126-mph record was set during a downgrade test run on Stoke Bank, south of Grantham, England, at Milepost 90 1/4.
New world record or not, T1 No. 5550 will be a sight to see: the styling of Loewy riding aboard an updated version of Baldwin and Franklin technology, spirited along by the contemporary version of Pennsylvania Railroad chutzpah courtesy of the T1 Trust. 2
For more information on the T1 Trust, please visit: prrt1steamlocomotivetrust.org
