Air binding is caused by pressure in the filters ______ than atmospheric pressure, and it can cause ______ flow.

• A. higher, increase in
• B. lower, resistance to
• C. lower, increase in
• D. higher, resistance to

Answer: (B)

Air binding happens when the pressure inside the filter bed drops below the surrounding atmospheric pressure. That negative pressure pulls air into the pores of the filter media, forming air pockets that disrupt continuous water pathways. Those air pockets create additional resistance to flow, reducing the effective flow through the bed. So the correct idea is that the pressure in the filters is lower than atmospheric, and this leads to increased resistance to flow. To prevent it, ensure proper venting and backwashing to remove trapped air and maintain an appropriate filtration rate.