Engineers usually design the height of a filter's backwash collection trough to allow for _____ bed expansion without loss of media into the troughs

Engineers usually design the height of a filter's backwash collection trough to allow for _____ bed expansion without loss of media into the troughs

• A. 25%
• B. 30%
• C. 40%
• D. 50%

Answer: (D)

The concept being tested is how much the filter bed can expand during backwash and how that expansion impacts whether media can enter the troughs. During backwashing, the bed rises and expands as water flows through it, so the troughs must be tall enough to accommodate that movement without the media being drawn into them. A design that allows a larger expansion margin gives a safer buffer against variations in backwash rate, media size, and bed depth, reducing the risk of media loss and fouling the collection system. Among the given options, choosing the largest expansion margin provides the most reliable protection against media loss, which is why that choice is considered best. Smaller margins would leave less clearance, increasing the chance that media enters the troughs during vigorous backwashing. In practice, the exact expansion depends on the media type and operating conditions, but the underlying idea is to provide sufficient clearance for the bed to expand without carrying media into the troughs.

The concept being tested is how much the filter bed can expand during backwash and how that expansion impacts whether media can enter the troughs. During backwashing, the bed rises and expands as water flows through it, so the troughs must be tall enough to accommodate that movement without the media being drawn into them. A design that allows a larger expansion margin gives a safer buffer against variations in backwash rate, media size, and bed depth, reducing the risk of media loss and fouling the collection system. Among the given options, choosing the largest expansion margin provides the most reliable protection against media loss, which is why that choice is considered best. Smaller margins would leave less clearance, increasing the chance that media enters the troughs during vigorous backwashing. In practice, the exact expansion depends on the media type and operating conditions, but the underlying idea is to provide sufficient clearance for the bed to expand without carrying media into the troughs.