5th. Open the scum or brine cocks and keep them open, also open all gauge or test cocks, etc., about the boiler.[72]
[72] It is not safe to draw the fire at a time when the pressure is at a dangerous point, especially if heavy, as disturbing it may temporarily increase the combustion and the danger of explosion.
[Figs. 3410] and [3411] represent an example of a steel marine boiler, designed for a working pressure of 160 lbs. per square inch, with a margin of safety of 5.
The dimensions are as follows:
| Diameter of shell | 12 feet | 6 | inches. | ||
| Shell plate | 1 | 1⁄8 | „ | thick. | |
| Front and back upper plates | 31⁄32 | „ | „ | ||
| Back rivet plates | 7⁄8 | „ | „ | ||
| Back lower plates | 7⁄8 | „ | „ | ||
| Front tube plate | 15⁄16 | „ | „ | ||
| Front lower plate | 13⁄16 | „ | „ | ||
| Furnaces | 17⁄32 | „ | „ | ||
| Inner tube plate | 3⁄4 | „ | „ | ||
| Combustion chamber back | 17⁄32 | „ | „ | ||
| Combustion chamber sides | 17⁄32 | „ | „ | ||
| Outer sides of wing combustion chambers | 9⁄16 | „ | „ | ||
| And bottom of centre one to be | 9⁄16 | „ | „ | ||
| Shell of receiver | 7⁄16 | „ | „ | ||
| Beds of receiver | 5⁄8 | „ | „ | ||
| Receiver connecting pipe | 3⁄4 | „ | „ | ||
The riveted joints have all holes drilled. The longitudinal seams are made with butt joints treble riveted, and with double butt straps.
The circumferential seams are lapped and treble riveted.
Fig. 3412.