The boiler can handle high steam pressure hence statement 3 is wrong.

Types of Boiler

The boilers can be classified according to the following criteria. According to the flow of water and hot gases:

1. Water tube
2. Fire tube

Water-tube boiler

• In water tube boilers, water circulates through the tubes, and hot products of combustion flow over these tubes.
• Water volume is large and due to poor circulation, they cannot meet quickly the change in steam demand.
• Water-tube boilers require less weight of metal for a given size, are less liable to the explosion, produce higher pressure, are accessible, and can respond quickly to change in steam demand.
• Tubes and drums of water-tube boilers are smaller than fire-tube boilers and due to the smaller size of drums, higher pressure can be used easily.
• Water-tube boilers require lesser floor space. The efficiency of water-tube boilers is more.

Fire Tube Boiler

• In a fire tube boiler, the hot products of combustion pass through the tubes, which are surrounded, by water. Fire-tube boilers have a low initial cost and are more compacts.
• For the same output, the outer shell of fire tube boilers is much larger than the shell of a water-tube boiler.
• They are low-pressure boilers. The operating pressure is about 25 bar.
• Externally fired fire tube boilers are locomotive-type boilers, horizontal return tubular (HRT) boilers, etc.
• Internally fired fire tube boilers are Scotch-marine boilers, Cochran boilers, package boilers, etc.