What is the recommended backwash rate expressed as vertical rise per minute?

• A. 1-2 gpm per square foot
• B. 50-60 inch per minute
• C. 5-10 inches per minute
• D. 20-30 inch vertical rise per minute

Answer: (D)

Backwash rate is described by how fast the filter bed vertically rises as water flows upward during cleaning. This vertical rise per minute tells you how aggressively the bed is being fluidized to lift and suspend trapped material.

The recommended value is a rapid rise on the order of 20 to 30 inches per minute. This range provides enough turbulence to fluidize and expand the bed so dirt and fines are flushed out, without washing away fine media or causing media loss. If you backwash too slowly, the bed won’t fluidize properly and cleaning won't be effective; if you go much faster, you risk carrying media out of the bed or creating excessive channeling. The other options don’t fit because they either express a different type of rate (volumetric gallons per minute per square foot) or are outside the typical, safe range for effective backwashing.