ANS:C - Blow off cock

A blow-off cock, also known as a blowdown valve or blow-off valve, is a crucial boiler fitting used for draining sediment, sludge, and impurities from the boiler. It's typically located at the lowest point of the boiler shell or at the bottom of the boiler's water space. Here's how it works:

1. Drainage of Impurities: Over time, sediment, scale, and other impurities can accumulate at the bottom of the boiler water space. These impurities can hinder heat transfer, reduce boiler efficiency, and even cause corrosion if left unchecked. The blow-off cock allows for the removal of these impurities by providing a means to drain water from the boiler.
2. Prevention of Scale Build-Up: In boilers, particularly those using hard water, minerals can precipitate out of the water and form scale deposits on the internal surfaces. These scale deposits can reduce heat transfer efficiency and lead to overheating of boiler components. Regular blow-down through the blow-off cock helps prevent the buildup of scale by flushing out concentrated mineral deposits.
3. Control of TDS (Total Dissolved Solids): Dissolved solids present in boiler feedwater can accumulate over time due to evaporation. If their concentration becomes too high, it can lead to boiler scaling, foaming, and carryover of impurities into the steam. Periodic blow-down through the blow-off cock helps control the TDS levels by removing a portion of the concentrated water along with dissolved solids.
4. Maintaining Water Quality: By periodically draining a small volume of water through the blow-off cock, operators can maintain the overall quality of the boiler water. This helps ensure that the boiler operates safely and efficiently over its service life.