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 Post subject: early super power
PostPosted: Fri Apr 27, 2018 9:03 pm 

Joined: Thu Oct 24, 2013 8:30 am
Posts: 94
did the earliest Lima super power had two smokestacks? if they did why? can somebody help me on this? I have read that older super power steamers had higher tractive effort and use less steam pressure than modern super power? Berk from the 20's generated over 76 thousand pounds of tractive effort than those from the late 30s and 40s which generated roughly 65,000 pounds of tractive effort. why is that


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 Post subject: Re: early super power
PostPosted: Mon Apr 30, 2018 5:30 pm 

Joined: Thu Dec 12, 2013 1:26 pm
Posts: 68
The early Lima "Super Power" Berks had 69,400lbs. tractive effort from the main cylinders plus 12,000lbs. from the booster for a total of 81,400lbs. starting tractive effort.
Another feature of the early super power era was Limited Maximum Cutoff. This is where the steam lap of piston valve is lengthened and closes (or cuts off the admission of steam) early in the power stroke. Lima commonly used 60% maximum cutoff. This theoretically reduces the peak of the tractive effort enabling larger cylinders and/or higher boiler pressure without causing the engine to slip. Larger cylinders and/or higher pressure also increased the minimum tractive effort, which increased the tractive at stall. This allowed a higher tractive effort for a given weight on the drivers, allowing a factor of adhesion of around 3.6 compared to more usual 4. A two cylinder locomotive has four somewhat modified sine waves of tractive effort that combine for an average traffic effort with four points in each revolution of the drivers having higher than average power and four valleys having less than average tractive effort. Limited cutoff lowered the maximum and raised the minimum tractive effort. Lima used 60%, because that was the cutoff that provided the most horsepower at normal road speed. Most locomotives only admitted steam the full power stroke upon starting. In order to start a heavy train the maximum cutoff had to be lengthened or increased. That was accomplished by machining slots or widening steam ports in the valve chest. After starting the amount of steam that was admitted after cutoff was very small. The other advantages were the larger cylinders/higher pressure generated higher horsepower at slow to medium speed, and it provided a wider port opening for a given cutoff which allowed more steam to enter the cylinders with less pressure loss at speed. Most roads found the engines were slippery and their maximum speed slower than it should have been. With a few notable exceptions, most engines built after around 1930 did not have limited cutoff. Most of the engines, with a few notable exceptions, that were built in the early super power era with limited cutoff, had the feature removed and became full stroke engines.
Tom


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 Post subject: Re: early super power
PostPosted: Mon Apr 30, 2018 10:12 pm 

Joined: Thu Dec 12, 2013 1:26 pm
Posts: 68
Early Lima super power engines had only one stack. Other than the newest engines on the UP and Pennsy, there was probably not too many engines with double stacks in the US.


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 Post subject: Re: early super power
PostPosted: Sat May 05, 2018 10:26 pm 

Joined: Thu May 24, 2012 1:37 pm
Posts: 1004
This thread doesn't belong in Railfanning, and it was a pathetic miscarriage of moderation to put it there. It is clear that the Interchange is for 'history' and not just preservation (in fact, you need read only to the fourth word and not the sixth of the Interchange's own definition of itself to find this out) and the question initially raised is intimately related to both the history and practice of locomotive design in significant ways.

What has become clear out of this debacle is that something needs to be forked with the Interchange to establish the possibility of having serious historical or technical threads that are not concerned with "preservation" per se. It shouldn't be intentionally hidden behind some nonintuitive mouse clicks, as Railfanning is from normal Interchange traffic, but I have no moral indignation about 'historical' subjects being put in their own section or even forum as long as there is some way to cross-reference them with similar material in the Interchange archives.

If that cannot be done, I seriously exhort the moderation team to consider putting this thread back where it belongs ... or modify the description of the Interchange to confirm that it is preservation/museum only.

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R.M.Ellsworth


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