As I recall, the boiler design of the D&H engines was really strange to me--and it may well have contributed to the high maintenance requirements. I can picture one or two of these engines in my mind (they really looked strange to me, back in the fifties, when Trains had an article on these engines).
Paul, was it the Vauclain that had a high pressure cylinder on one side and a low pressure cylinder on the other? Or did it have a high and low pressure cylinder on each side? I confess that I had not heard the name "de Glehn;" what was the cylinder arrangement?
Johnny
There's a big difference between a marine VTE engine, which operates at relatively low speeds, and a Vauclain or de Glehn compound, which are high speed designs. Also, most of the early compound designs were withdrawn with the advent of superheating.
The various D&H experimentals in the 1400 series were complex high-maintenance designs. It was said that they could pull well but you had to send half of the shop force out with them.
Since compounding in the United States was mostly in the form of Mallet locomotives, with their ponderous low pressure cylinders and low drivers, there is a general impression that compounds were inherently slow.
`T`aint necessarily so.
Some of the Cole and Vauclain compounds built around the turn of the last century were high-drivered 2-4-2 and 4-4-2 types, and were quite capable of a good turn of speed. More recently, there were compounds built on the far side of the Atlantic that could FLY!
Back in the early '70s, Bill Withuhn designed a 4-cylinder triple expansion compound engine that used internally connected drivers to balance and all but eliminate dynamic augment. If built, it would have been capable of speeds comparable to a N&W J.
One key difference between the Mallet and a four cylinder triple expansion loco is that three of the four cylinders are meant be the same size - greatly simplifying the balancing required.
So, are such engines practical? Innumerable ocean-going ships had four cylinder triple expansion engines, including all the WWII Liberty ships. They were chosen for the latter because they were simple, reliable and didn't require reduction gears like a steam turbine.
There was one such loco built in the US - the Delaware and Hudson's Leonor F. Loree. It was a low-drivered 4-8-0, basically a super-consolidation, not designed for speed. The limiting factor was driver size, not compounding.
Chuck
You're welcome, Ulrich!
Interesting response...thanks Firelock!
Well, yes and no. Yes, the double use of steam from high pressure to low pressure cylinders is a bit more efficient, but there is a penalty paid in road speed. The Big Boys and Challengers were designed for 70mph running so compounding just wouldn't work. The Norfolk and Western's Y6 Mallets could get up to 50mph but I don't think they were run that fast very often. The Class A simple articulated was a greyhound though, 60-plus mile per hour running was nothing for them.
Most compound Mallets were used in drag freight and pusher service, so speed wasn't a factor.
Looking forward to hearing from others on this one!
What are the advanatges of one over the other? Union Pacific Big Boy and Challenger locomotives were simple expansion with the same steam pressure applied to all four cylinders. The Norfolk and Western opted for true Mallets..compound expansion locomotives where steam was first used in the hind two cylinders and then routed for further expansion in the two oversized front cylinders. One might think that the Mallet might be more efficient as the same steam is used twice before being dissipated to the atmosphere..is that correct?
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