CPI Sand, DE & Cartridge Filtration 3

Question 1

What is the primary reason a sand filter requires a 'Rinse' cycle after backwashing?

Accepted Answer

To settle the sand bed and flush loosened particles to waste

Answer

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.

Question 2

When inspecting a DE filter, the inspector should verify that the manual air relief valve:

Accepted Answer

Opens to release trapped air when the system is started

Answer

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.

Question 3

A pool cartridge filter has a dirty pressure reading 25 PSI above its clean baseline. The inspector should note this as:

Accepted Answer

A sign the cartridge needs cleaning or replacement

Answer

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.

Question 4

Which chemical should NEVER be used to clean a DE filter grid or cartridge filter element because it destroys the filter media?

Accepted Answer

Muriatic acid

Answer

Muriatic acid can damage or dissolve the polyester or polypropylene fabric of filter grids and cartridge elements, causing media failure.

Question 5

In a sand filter, what term describes the condition where oil, sunscreen, and organic matter bind the sand granules into a solid mass?

Accepted Answer

Mudballing

Answer

Mudballing occurs when oils and organics cement sand particles together into clumps, drastically reducing the media's filtering surface area.

(CPI) Certified Pool & Spa Inspector Practice Test

(CPI) Certified Pool & Spa Inspector Practice Test

CPI Sand, DE & Cartridge Filtration 3