Sand, DE & Cartridge Filtration Flashcards
7 cards from real CPI practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Sand, DE & Cartridge Filtration flashcards as text
What is the primary reason a sand filter requires a 'Rinse' cycle after backwashing?
Answer: To settle the sand bed and flush loosened particles to waste
The Rinse cycle briefly returns flow in the normal filter direction to re-settle disturbed sand and send any remaining loosened debris out the waste port before returning to Filter mode.
When inspecting a DE filter, the inspector should verify that the manual air relief valve:
Answer: Opens to release trapped air when the system is started
The air relief valve bleeds trapped air from the filter tank on startup; a stuck-closed valve can cause air locks that reduce flow and filtration efficiency.
A pool cartridge filter has a dirty pressure reading 25 PSI above its clean baseline. The inspector should note this as:
Answer: A sign the cartridge needs cleaning or replacement
A pressure rise of 8–10 PSI or more above the clean baseline is the standard trigger to clean or replace a cartridge filter element.
Which chemical should NEVER be used to clean a DE filter grid or cartridge filter element because it destroys the filter media?
Answer: Muriatic acid
Muriatic acid can damage or dissolve the polyester or polypropylene fabric of filter grids and cartridge elements, causing media failure.
In a sand filter, what term describes the condition where oil, sunscreen, and organic matter bind the sand granules into a solid mass?
Answer: Mudballing
Mudballing occurs when oils and organics cement sand particles together into clumps, drastically reducing the media's filtering surface area.
What is the standard DE dosage used when recharging a DE filter after a complete cleaning?
Answer: Manufacturer-specified amount based on filter square footage
DE dosage is determined by the filter manufacturer based on total grid surface area (typically 1 lb per 10 sq ft), not pool volume.
An inspector observes white powder returning through the pool return jets immediately after a DE filter is recharged. The MOST probable cause is:
Answer: Torn or failed grid fabric allowing DE bypass
DE returning to the pool immediately after recharging almost always indicates a torn grid or manifold crack that allows the powder to pass through the filter.