What is main demerit of water tube boilers over fire tube boilers?

What is main demerit of water tube boilers over fire tube boilers? Correct Answer Failure in feed water supply even for short period is liable to make the boiler overheated.

Explanation:

Demerits of Water Tube Boiler over Fire Tube Boiler:

• It is less suitable for impure and sedimentary water, as a small deposit of scale may cause the overheating and bursting of the tube. Therefore, use of pure feed water is essential.
• They require careful attention. The maintenance costs are higher in water tube boiler compared to fire tube boiler.
• Failure in feed water supply even for a short period is liable to make the boiler overheated.

Additional InformationMerits of Water Tube Boiler over Fire Tube Boiler:

• Generation of steam is much quicker due to the small ratio of water content to steam content. This also helps in reaching the steaming temperature in short time.
• Its evaporative capacity is considerably larger, and the steam pressure range is also high 200 bar.
• Heating surfaces are more effective as the hot gases travel at right angles to the direction of water flow.
• The combustion efficiency is higher because complete combustion of fuel is possible as the combustion space is much larger.
• The thermal stresses in the boiler parts are less as different parts of the boiler remain at uniform temperature due to the quick circulation of water.
• The boiler can be easily transported and erected at its different parts can be separated.
• Damage due to the bursting of water tube is less serious. Therefore, water tube boilers are sometimes called safety boilers.
• All parts of the water tube boiler are easily accessible for cleaning, inspecting and repairing compared to fire tube boiler.
• The water tube boiler’s furnace area can be easily altered to meet the fuel requirements.