3 cylinder compound steam locomotives

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April 21, 2013 8:44 PM

How does a 3 cylinder compound steam locomotives work? If the inside high pressure cylinder feeds the 2 outside low pressure cylinders, doesn't it have to work twice as much as the low pressure cylinders?

 
 
 
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April 21, 2013 8:54 PM

I thought that the two outside cylinders are the high pressure, which then feeds their exhaust steam to the inside, low pressure cylinder. The low pressure cylinder is always larger in diameter to allow for the lower temperature steam, but all three, or four cylinders do the same "work".

 

I must admit however, that all the three cylinder steam locomotives I've seen in Germany all had the three cylinders working with high pressure steam. Thus, they where not compound. 

 
 
 
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April 21, 2013 10:30 PM

Looking at the Wikipedia entry on compound locomotives, seems like there weren't too many three cylinder compounds made.  Baldwin 60000 seems like the only one made in the states, with the center cylinder as the high pressure one and the outers as low pressure.  My understanding of compounds is that the subsequent cylinders in a compound need to have twice the volume of the previous cylinder.  Since the 60000 had all the cylinders at 27x32, the combined volume of the LP cylinders was twice the HP's volume. 

 

More info at the compound steam engine article. I'm sure someone who understands such stuff better will correct me, in which case, thank you!

 

 
 
 
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April 21, 2013 10:41 PM

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.

 
 
 
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April 21, 2013 10:44 PM

AFAIK, the only three-cylinder compound built for use in the USA was the 4-10-2 Baldwin demonstrator #60000, which now resides in the Franklin Institute in Philadelphia.

 

The center cylinder was/is high-pressure, the two outer cylinders low-pressure.  The two outer cranks were 90 degrees apart with left-hand lead; the center crank was 135 degrees from both of the outer cranks.  Since Alco had the license for the English Gresley valve gear for operating the valve of the center cylinder of a locomotive whose cranks were 120 degrees apart, Baldwin had to resort to a different method.

 

Again, AFAIK the engine performed well enough, but had a water-tube firebox and steamed at 350 pounds; it had so many novel features that nobody was interested in buying it.

 

The center cylinder has an inside-admission piston valve getting its motion from an oddly-set eccentric crank on the right side; its combination lever is inside.  The left valve is an outside-admission piston valve with the normal arrangement of Walschaerts valve gear.  The Walschaerts link for the right valve, also outside admission, gets its motion from the left crosshead, which has a lever that drives a shaft across the frame.

 

Don't know whether Baldwin really expected to sell any of these, but nobody was interested in either the water-tube firebox (the firebox alone has 200 washout plugs to be removed and replaced every monthly boiler wash; an N&W Y-6 2-8-8-2 had 39 in firebox and boiler combined) or the drive train.

 

Alco did use the wheel arrangement for 3-cylinder simple engines for the UP and SP, though.  The cranks of these engines were 120 degrees apart, and they used the Gresley arrangement.

 

EdKing

 
 
 
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April 21, 2013 11:54 PM

200 washout plugs?  Good thing Betty Cole was selling them cheap.

 


sorry - this photo has been posted before.  It usually stops the thread cold.

 
 
 
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April 22, 2013 8:12 AM

Originally Posted by bob2:

200 washout plugs?  Good thing Betty Cole was selling them cheap.

 


sorry - this photo has been posted before.  It usually stops the thread cold.

Nice model, but the eccentric crank is set for an inside-admission cylinder (can't tell if the connection between the radius rod and combination lever is correct).  For an outside-admission valve, the eccentric crankpin should lead the main crankpin; here it is set up to follow it.

 

Don't know why it was designed that way, but with the inside cylinder inside admission, they could have designed direct porting from the inside cylinder exhaust to the outer cylinders intake. 

 

Not a bad looking engine, though.  Who built the model?

 

EdKing

 
 
 
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April 22, 2013 9:17 AM

 Thanks guys, it makes since now. Yes,I was thinking of the Baldwin 60000. I could have saved myself a lot of time by going to this form first, instead going through my books, old magazine and web searching.

 Thanks Edward King about explaining the crank axle spacing of 90 and 135 degrees, I thought the spacing was 120 degrees.

 
 
 
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April 22, 2013 11:17 AM

Originally Posted by Edward King:

AFAIK, the only three-cylinder compound built for use in the USA was the 4-10-2 Baldwin demonstrator #60000, which now resides in the Franklin Institute in Philadelphia.

 

The center cylinder was/is high-pressure, the two outer cylinders low-pressure.  The two outer cranks were 90 degrees apart with left-hand lead; the center crank was 135 degrees from both of the outer cranks.  Since Alco had the license for the English Gresley valve gear for operating the valve of the center cylinder of a locomotive whose cranks were 120 degrees apart, Baldwin had to resort to a different method.

 

 

EdKing

Thanks Ed. I obviously had it "backwards" since I have never been around any compound locomotives, except the N&W "Y" class. All the three cylinder locomotives I saw in Germany were NOT compound, and had really great sounding exhausts, especially under heavy load & full throttle.

 

Thanks again for setting me straight. 

 
 
 
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April 22, 2013 11:46 PM

Ed - I just copied whatever photos and drawings I could find, which was not much.  The model has fully functioning double Walschaerts gear, and a center main rod.  My 3-cylinder locomotives all feature a functioning center rod and as accurate valve gear as possible.  I do cheat when it comes to cranked axles - those are for the real pros.

 

It really does have a bunch of 0-80 hex heads simulating the washout plugs.

 

My next is a 4-12-2, and it already runs - the boiler is pretty much bare, but someday - 

 
 
 
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April 23, 2013 5:00 PM

Originally Posted by morg777:

 My understanding of compounds is that the subsequent cylinders in a compound need to have twice the volume of the previous cylinder. 

 

The 2 to 1 ratio evidently worked pretty well on the 60000, but Mallet designers learned early on that a better ratio was about 2 1/2 to 1.  The ground-breaking Alco 2-6-6-2 that became the C&O H-1 of 1910 had that ratio, with high-pressure cylinders of 22" diameter, low-pressure cylinders of 35" diameter with a 32" stroke.  This ratio was also present on N&W's first Mallets, the X-1 0-8-8-0 and Y-1 2-8-8-2 of 1910, with their 24 1/2" high-pressure cylinders and 39" low-pressure cylinders with the 32" stroke. 

 

These cylinder dimensions were used on N&W's Y-2 2-8-8-2 of 1918 with a higher boiler pressure.  The USRA 2-8-8-2 modified this ratio by using a 25" high-pressure cylinder, and all N&W's subsequent 2-8-8-2s retained these cylinder dimensions.

 

EdKing 

 

 
 
 
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