high-rate sand filters for swimming pools work on a vacuum principle much like an ordinary vacuum cleaner. the filter draws in water instead of air (this is why air in the filter system or lines in unwanted - air will cause the "vacuum" pressure to fall). submerged and suspended particles are drawn in from the bottom drains while surface floating debris is drawn in through the skimmer assembly.

which statement would be the best final sentence in a conclusion on the topic of sand filter maintenance?
a) the pump will cause water to flow from the pool through the hair and lint pot.
b) set the pump on backwash whenever it needs to be cleaned with the cleaning process.
c) the multiport valve on the pump controls the flow of water depending on the setting.
d) over time the sand bed will become plugged with dirt and require a cleaning process known as backwashing.