No. 17. Straight horizontal headers were next tried, alternately shifted right and left to allow a staggering of tubes. These headers were connected to each other [Pg 45] and to the drums by expanded nipples. The objections to this boiler were almost the same as those to No. 16.
| No. 18 | No. 19 |
Nos. 18 and 19. These boilers were designed primarily for fire protection purposes, the requirements demanding a small, compact boiler with ability to raise steam quickly. These both served the purpose admirably but, as in No. 9, the only provision made for the securing of dry steam was the use of the steam dome, shown in the illustration. This dome was found inadequate and has since been abandoned in nearly all forms of boiler construction. No other remedy being suggested at the time, these boilers were not considered as desirable for general use as Nos. 21 and 22. In Europe, however, where small size units were more in demand, No. 18 was modified somewhat and used largely with excellent results. These experiments, as they may now be called, although many boilers of some of the designs were built, clearly demonstrated that the best construction and efficiency required adherence to the following elements of design:
1st. Sinuous headers for each vertical row of tubes.
2nd. A separate and independent connection with the drum, both front and rear, for each vertical row of tubes.
[Pg 46]
3rd. All joints between parts of the boiler proper to be made without bolts or screw plates.
4th. No surfaces to be used which necessitate the use of stays.
5th. The boiler supported independently of the brickwork so as to allow freedom for expansion and contraction as it is heated or cooled.
6th. Ample diameter of steam and water drums, these not to be less than 30 inches except for small size units.