ANS:C - drain out the sludge from the drum.

The function of a blow down valve in a boiler is to drain out the sludge from the drum. Explanation:

• Blow down valves are essential components in boiler systems designed to remove impurities, sediment, and dissolved solids (referred to as sludge) that accumulate at the bottom of the boiler drum.
• Continuous operation of the boiler leads to the concentration of impurities in the boiler water, which can cause scaling, corrosion, and reduced boiler efficiency if not removed.
• The blow down valve is opened periodically to discharge a portion of the boiler water along with the accumulated sludge, helping to maintain the water quality within acceptable limits.
• By removing the sludge, blow down valves help prevent scale formation, reduce corrosion, and ensure optimal boiler performance and longevity.
• The blow down process also helps control the concentration of dissolved solids in the boiler water, preventing excessive build-up that could lead to boiler damage or inefficiency.
• Blow down valves are typically operated manually or automatically based on preset parameters such as water conductivity or dissolved solids concentration.