Steam & Excursion > In Full Stride

John S. Powell caught 3320, a K2 turned out by Juniata in 1910, leading a ten car train at Narberth, 1913. The date on this photo might actually be accurate. And just to muddy the waters, the Pennsy Modeler database shows this locomotive as both a K2 and K2s.
Photo credit the Library of Congress, Bruce Fales collection
Be of good cheer,
—Mac
www.lowellamrine.com

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I am thinking the K2's were originally not superheated, but very shortly after they were built they were equipped, but I could be thinking wrong.

Another first-class historical image.
Bob

It does not appear that the locomotive in the picture has the characteristic 5 bolt superheater attachment pattern on the smokebox, so that this is still a K2.  

For what it's worth, the Pennsy Modeler states the 3320 became a K2s in August 1912, something that should have been noted in the caption.
—Mac

elueck Wrote:
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> It does not appear that the locomotive in the
> picture has the characteristic 5 bolt superheater
> attachment pattern on the smokebox, so that this
> is still a K2.  

Interestomg.  Obviously Pennsy did things differently

For us non-experts of Pennsy steam power, what were the essential diffences between the K2 and K4 classes?  How long did the K2's last after the K4's took over?

I guess the 3 /4 wedgie was the big thing back then. 

Not that there's anything wrong with that.

Prototype K4 1737 was built in 1914. In 1917, 41 were built, the last 8 of the 425 came in 1928.
—Mac

Earlk Wrote:
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> For us non-experts of Pennsy steam power, what
> were the essential diffences between the K2 and K4
> classes?  How long did the K2's last after the
> K4's took over?

I am no expert on PRR power or steam locomotives, but I have stayed at a few Holiday Inn Expresses and read what I can find. Admittedly my PRR resources here at home are not what I wish they could be as the PRR was a fascinating railroad. Anyhow, related to the K2 and K4.

K2's prototype was the K28 in 1907. It proved successful as a means to handle the ever increasing train weights and demand on the pre- E6 Atlantics. Both the k28 and the K2's were the products of David F. Crawford, Supt. of Motive Power Lines West based in Fort Wayne, IN. Upon review the K2 was thought to be superior to the K1 designed by Altoona, and that concept never got beyond the drawing board. K2's starting coming out in 1910.

K2's:
24x26, 80 inch drivers, 205 psi, 32,620 # T.E. 
Heating surface: 4629 sq. ft. - as built saturated.
Grate Area: 55.38 sq. ft.

K4s:
27x28, 80 inch, 205 psi, 44,460 # T.E.
Heating surface; 4984 + 943 superheating sq ft.
Grate Area: 69.89 sq ft.

K2 was the original version, K2s was the superheated rebuild a few years later. My understanding is the super heater did not help the steaming ability much for some reason.
K2a was the Crawford modification loco sub-class for the underfeed stoker installation. How many actually got stokers i do not know. The firing deck was raised higher, hence the sub-class. K2as were superheated.

The K2 classes were never particularly liked. Noted as poor steamers, hand fired and not capable of reaching the full potential of a 4-6-2 with that size boiler, but a stop gap until bigger and better Atlantics and a better Pacific could be developed. One major criticism of the K2 was the manual Johnson Bar with the heavy and massive valve gear and machinery. The 16 inch pistons weighed 244 lbs, and link shafts, links and supporting structure were deemed too heavy.  Many engine men would just set the reverser and leave it and work the throttle.  Between Manhattan Jct. and Washington, DC it was said the K2's consumed 15 tons of hand shoveled coal. They were briefly tried in Suburban service but did not fare well. The Fort Wayne and lines west is where they really shined, but were still lacking. This led Crawford to develop the K3's with underfeed stokers and pistons 2 inches in diameter larger. Another issue with the K2 was the trailing trucks frequently developing hot boxes.

There were two K2b's, modified K2's by Alfred Gibbs of Altoona Mechanical which were fitted with 72 inch drivers and assigned to Lines West where they reportedly turned in good performances although no others were altered.

Eventually in November 1911 Gibbs, working closely with Alco developed the K29 which was the prototype for the K4s and became PRR's passenger standard. Gibbs also developed the ultimate Atlantic type, the Class E6s.

Most of the K2's were gone by the late 1930's, but a few held out until after WWII sometime. As PRR mechanical noted, they were a stop-gap locomotive, useful for the time but quickly superseded by better power.

Both K2 and K4s' had Belpaire fireboxes.



Edited 3 time(s). Last edit at 02/17/26 10:37 by train1275.

> For what it's worth, the Pennsy Modeler states the
> 3320 became a K2s in August 1912

But far as we can tell from the pic,
3320 has no superheat?

timz Wrote:
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> > For what it's worth, the Pennsy Modeler states
> the
> > 3320 became a K2s in August 1912
>
> But far as we can tell from the pic,
> 3320 has no superheat?

Don't see it

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Look at that knife-edge on the ballast!

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