A dual-media filter is backwashed at a rate of 18.0 gpm/sq ft. What is the equivalent backwash rise rate expressed in inches per minute (in/min)?

Formula Used: Rise Rate (in/min) = [Backwash Rate (gpm/sq ft) × 12 in/ft] ÷ 7.48 gal/cu ft

Step-by-Step Mathematical Derivation:

1. Convert gpm/sq ft to vertical rise in ft/min: 18.0 ÷ 7.48 = 2.4064 ft/min.
2. Convert feet to inches: 2.4064 ft/min × 12 in/ft = 28.88 in/min (~28.9 in/min).

⚠️ Common Exam Trap: Operator exam shortcut: Rise Rate (in/min) = gpm/sq ft × 1.604.