That sounds logical. As far as I know, all American 3-cylinder locomotives used high-pressure steam in all cylinders - with one exception.
In the 1920's steam locomotive development had reached maximum allowable size and weight limits. Three cylinders added power within those limits. Following European practice, the first were 4-6-2's and 4-8-2's. But gains were negligible. Larger locomotives - 4-10-2's - performed well on the UP and on the SP. Always thinking big, the UP expanded the concept and acquired 88 4-12-2's. Then maintenance costs began to mount. Smaller European locomotives were able to use 3 cylinders and 4 cylinders (and cranked axles) economically. Their running gear could handle the power produced.
ALCo was thriving in the 3-cylindr market. Baldwin's business dropped to jobs that ALCo was too busy to handle. Baldwin tried to enter the market by taking the 3-cylinder concept to the next level - America's only 3-cylinder compound.
A water-tube firebox was used to supply steam at 350 lbs. It went to a high-pressure center cylinder and exhausted to both outside cylinders. It was numbered 60000 as the 60,000th locomotive built by Baldwin. It produced more than 4500 hp and exceeded the capacity of the Pennsy test plant at Altoona. But it was too big, heavy and complex for railroad operating departments. It was returned to Baldwin after a 100,000-mile demonstrator tour, unsold and unwanted. Baldwin Vice-President Samuel L. Vauclain served on the Board of The Franklin Institute. He arraged to donate her to Railroad Hall in 1932, where she has moved back and forth about 10 feet to give cab rides to visitors ever since.
Lima cracked the horsepower/weight barrier with a larger firebox supported by a 4-wheel trailing truck. Lima Super Power accomplished what 3-cylinder power did not - steam and power at increased speeds.
That was the second time Mr. Vauclain fell short. He invented Vauclain compounds - high pressure cylinders atop low-pressure cylinders. They met some success until superheaters did a better job with pipes inside boiler flues to increase steam temperature and give it more expansive force.
