The Atlantic-type steam locomotive is represented in the Museum
collection by a nonoperable model (figure 74) lent to the Museum in 1922
by E. Howard Askew of Baltimore, Md. Constructed by the lender, the
model (USNM 307949) is 32 inches long and has a gauge of 2½ inches.
It represents the Pennsylvania Railroad class E3sd _No. 5127_, a 4-4-2
steam locomotive with Walschaert valve gear. The original locomotive was
built at the railroad’s Juniata shops, Altoona, Pa., in August 1907,
construction No. 1734. Originally a class E3d locomotive, it was
converted to an E3sd in June 1913 by the addition of a superheater in
the Wilmington, Del., shops of the road.
[Illustration: Figure 74.—Model of Pennsylvania Atlantic-type
locomotive, 1907.]
In a letter to Askew (Dec. 14, 1922) the chief of motive power of the
Pennsylvania System, J. T. Wallis, stated that the cylinders of the
original had a bore and stroke of 22 and 26 inches. The drivers were 80
inches in diameter and the boiler carried a steam pressure of 205
pounds. The boiler had a minimum (internal) diameter of 65½ inches, and
it contained 170 2-inch flues and 24 5½-inch flues, while the
superheater consisted of 96 1½-inch flues. The distance between flue
sheets was 180 inches and the total heating surface was 2,571 square
feet. The grate was 111 inches long and 72 wide.
The total weight on the drivers was 127,200 pounds, on the engine truck
35,500 pounds, and on the trailer truck 33,900 pounds—or a total of
196,600 pounds in working order. The weight of the tender in working
order was 134,000 pounds. The tractive force of the locomotive was
27,409 pounds.
In his letter Wallis also made the following statement to explain the
significance of the modification of this class of locomotive:
The Atlantic, or 4-4-2, type locomotive was developed in an effort to
retain the desirable features of the American, or 4-4-0, type of
locomotive and at the same time to produce a locomotive in answer to
the demand for greater power. To do this, the firebox was increased in
area by making it considerably wider, so that a greater amount of soft
coal could be burned. The diameter of the barrel of the boiler was
increased to allow for greater heating surface, which, of course,
increased the weight on the drivers.
To make room for the driving wheels without unduly increasing the
length of the tubes in the boiler, the driving wheels were moved
forward, the main driver being in the rear instead of in front as in
the American type locomotive. In order to carry the weight of the
firebox, which, with the new driving wheel location, overhangs the
rear driver too much to be properly supported, a two-wheel trailer
truck was used. This trailer truck, which is fulcrumed a short
distance back of the main driver, is so designed that it has lateral
motion, and provision is made for ash pan as well as firebox
clearance.
By the use of higher steam pressure, larger heating surface and grate
area, the use of passenger locomotives of the three-coupled type, with
the troubles incident to the use of long parallel rods, was put off
for a decade.