Figure 1-1 is a portable Scotch marine tire-tube boiler. The portable unit can be moved easily and requires only a minimal amount of foundation work. As a complete self-contained unit. its design includes automatic controls. a steel boiler. and burner equipment. These features are a big advantage because no disassembly is required when you must move the boiler into the field for an emergency.
The Scotch marine boiler has a two-pass (or more) arrangement of tubes that run horizontally to allow the heat inside the tubes to travel back and forth. It also has an internally fired furnace with a cylindrical combustion chamber. Oil is the primary fuel used to fire the boiler; however. it can also be fired with wood, coal, or gas. A major advantage of the Scotch marine boiler is that it requires less space than a water-tube boiler and can be placed in a room that has a low ceiling.
The Scotch marine boiler also has disadvantages. The shell of the boiler runs from 6 to 8 feet in diameter, a detail of construction that makes a large amount of reinforcing necessary. The fixed dimensions of the internal surface cause some difficulty in cleaning the sections below the combustion chamber. Another drawback is the limited capacity and pressure of the Scotch marine boiler.
An important safety device sometimes used is the fusible plug that provides added protection against low-water conditions. In case of a low-water condition. the fusible plug core melts, allowing steam to escape, and a loud noise is emitted which provides a warning to the operator. On the Scotch boiler the plug is located in the crown sheet, but sometimes it is placed in the upper back of the combustion chamber.
Access for cleaning, inspection, and repair of the boiler watersides is provided through a manhole in the top of the boiler shell and a handhold in the water leg. The manhole opening is large enough for a man to enter the boiler shell for inspection, cleaning, and repairs. On such occasions, always ensure that all valves are secured, locked, tagged, and that the person in charge knows you are going to enter the boiler. Additionally, always have a person located outside of the boiler standing by to aid you in case of an incident occurring that would require you to need assistance. The handholds are openings large enough to permit hand entry for cleaning, inspection, and repairs to tubes and headers. Figure 1-2 shows a horizontal fire-tube boiler used in low-pressure applications.
1. VENTS
2. AIR DAMPER
3. HIGH-LIMIT PRESSURE CONTROL
4. STEAM PRESSURE GAUGE
5. GAUGE GLASS SHUTOFF COCK
6. LOW-WATER CONTROL
7. WATER LEVEL GAUGE
8. BURNER SWITCH
9. PRIMING TEE
10. OIL UNIT, TWO STAGE
11. SOLENOID OIL VALVE (Maintenance)
12. SERVICE CONNECTION BOX
13. FUEL OIL SUPPLY CONNECTION
14. FUEL OIL PRESSURE GAUGE
15. IGNITION CABLE
16 IGNITION CABLE
17. NAMEPLATE
18. BLOWER MOTOR
