No. 14. A wrought-iron box was substituted for the double cast-iron headers. In this design, stays were necessary and were found, as always, to be an element to be avoided wherever possible. The boiler was an improvement on No. 6, however. A slanting bridge wall was introduced underneath the drum to throw a larger portion of its heating surface into the combustion chamber under the bank of tubes.
This bridge wall was found to be difficult to keep in repair and was of no particular benefit.
No. 15
No. 15. Each row of tubes was expanded at each end into a continuous header, cast of car wheel metal. The headers had a sinuous form so that they would lie close together and admit of a staggered position of the tubes when assembled. While other designs of header form were tried later, experience with Nos. 14 and 15 showed that the style here adopted was the best for all [Pg 44] purposes and it has not been changed materially since. The drum in this design was supported by girders resting on the brickwork. Bolted joints were discarded, with the exception of those connecting the headers to the front and rear ends of the drums and the bottom of the rear headers to the mud drum. Even such joints, however, were found objectionable and were superseded in subsequent construction by short lengths of tubes expanded into bored holes.
No. 16
No. 16. In this design, headers were tried which were made in the form of triangular boxes, in each of which there were three tubes expanded. These boxes were alternately reversed and connected by short lengths of expanded tubes, being connected to the drum by tubes bent in a manner to allow them to enter the shell normally. The joints between headers introduced an element of weakness and the connections to the drum were insufficient to give adequate circulation.
