Backwashing uses reverse flow to clean exchanger tubes by removing what?

• A. Rust
• B. Scale
• C. Debris
• D. Bacteria

Answer: (B)

Backwashing relies on reverse flow to flush out deposits that clog exchanger tubes. The deposits in question are scale—mineral buildup such as calcium and magnesium compounds that precipitate from process or cooling waters and adhere to the tube surfaces. Reversing the flow creates a sweeping action that loosens and carries these hard, adhered particles out of the tubes, restoring flow and heat transfer efficiency. Rust or debris might be removed by flushing in some situations, but scale is the specific buildup addressed by backwashing in many exchanger cleaning applications, and bacteria typically requires sanitization rather than flushing.