In pressurized drip irrigation header assemblies, silica media filters (gravel/sand beds) are automatically backwashed when the pressure differential ($\Delta P$) across the bed reaches approximately:
Options:
(A) $0.3$ to $0.5\text{ bar}$ ($30$ to $50\text{ kPa}$ or $3$ to $5\text{ m head loss}$)
(B) $5.0\text{ bar}$
(C) $0.01\text{ bar}$
(D) $10.0\text{ bar}$
Answer Key:
A
Step-by-Step Solution & Explanation
A clean sand media filter operates with a head loss of $0.2-0.3\text{ bar}$. When accumulated organic/algal cake builds a differential $\Delta P \approx 0.3-0.5\text{ bar}$ ($5\text{ psi}$ rise), automated backwash valves reverse flow to fluidize and clean the media bed.