What is the purpose of turning off surface washers before the end of the backwash?

• A. To protect media
• B. To save energy
• C. To shorten backwash time
• D. To improve filtration

Answer: (A)

The main idea is to protect the filter media. During backwash, the bed is lifted and cleaned by upward flow, and surface washers help scour the top layer. If the surface washers keep running too late in the cycle, they can over-agitate the top of the bed and cause fines or even some media to be carried out of the filter, bending or removing the valuable media that forms the bed. Turning them off before the end reduces this excessive agitation, preserving the media and maintaining the bed’s structure for future filtration. While surface washing can aid cleanliness, leaving it on past the point of effective cleaning doesn’t improve filtration and can damage the media.