CPI Sand, DE & Cartridge Filtration 2

Question 1

What is the typical operating pressure range for a properly functioning sand filter?

Accepted Answer

8–15 PSI

Answer

Sand filters normally operate between 8–15 PSI at startup; a rise of 8–10 PSI above the clean baseline signals that backwashing is needed.

Question 2

Which sand filter component prevents sand from passing back into the pool during normal filtration?

Accepted Answer

Lateral assembly

Answer

Laterals are slotted tubes at the bottom of the sand bed whose narrow slots allow water through but retain sand particles.

Question 3

A pool inspector notices the sand filter sight glass remains cloudy after a full backwash cycle. The MOST likely cause is:

Accepted Answer

Channeling through the sand bed

Answer

Channeling creates bypass paths through the sand so water is never fully filtered, leaving effluent turbid even after backwashing.

Question 4

DE filter grids must be inspected for which defect that allows DE powder to pass into the pool?

Accepted Answer

Tears or holes in the fabric

Answer

Torn or deteriorated grid fabric allows DE powder to bypass filtration and return to the pool, appearing as white cloudy material.

Question 5

What is the correct procedure after adding fresh DE powder to a DE filter following a backwash?

Accepted Answer

Add powder directly into the skimmer with the pump running

Answer

DE powder is slurried and poured into the skimmer with the pump running so it coats the grids evenly inside the filter.

(CPI) Certified Pool & Spa Inspector Practice Test