Function

• All swimming pool filters work by trapping dirt and debris inside the filter tank as pool water is circulated through the filtration system. With a sand or diatomaceous earth filter, as the amount of dirt and debris builds up in the tank, the pressure with which the water moves through the filtration system increases. Once the pressure gauge reads 8 to10 lbs. per square inch (psi) higher than the clean starting pressure, it is time to clean or backwash the filter.
  
  

Features

• Both DE and sand filters come equipped with pressure gauges, a multiport or slide valve and a sight glass, all of which are used for backwashing the filter. A multiport valve has multiple “ports” or positions on a rotating valve--typically six positions. A slide valve is simply a push-pull T-shaped valve. Backwashing involves turning one of these valves so the water flows backward through the filter, flushing out dirt and debris. The sight glass is used to watch for the dirty water to become clear as it goes through the backwashing process.
  
  

Filter Media

• Sand swimming pool filters use special silica sand as the filter medium. Rather than being smooth and rounded, the sand is rough and square-shaped, which allows it to trap dirt and debris particles as small as 20-100 microns (a micron is one-millionth of a meter) in the filter tank. Diatomaceous earth filters use diatomaceous earth powder as a filter medium. When the powder is added to the tank it coats a set of filter grids located in the tank. DE filters can trap particles as microscopic as 3-5 microns.
  
  

Valve Positions/Cycles

• Typically the positions on a DE or sand filter’s multi-port valve include “Filter,” “Rinse,” “Recirculate,” “Backwash,” “Closed” and “Waste/Drain.” Filters are set on the “Filter” position generally 99 percent of the time, except when backwashing. During the backwashing process, the backwash, rinse and filter settings are used. On the recirculate setting, the water returns directly to the pool from the pump without going through the filter. If the filter is broken, this setting can be used to at least circulate the pool water. The closed setting will stop the flow of water from the pool and is used when working on the filter equipment. The waste/drain setting sends the water through the waste hose rather than returning it to the pool and can be used to lower the water level in the pool.
  
  

Rinse Cycle

• The swimming pool filter is turned to the rinse setting immediately after running the backwash cycle for 3 to 5 minutes. Typically, the rinse cycle is run for 30 seconds to one minute. In a sand filter, the rinse cycle allows water to flow back down through the sand to flush out any remaining dirt and debris from the filter and piping. The rinse cycle also restratifies (deposits in layers) the sand, letting it resettle in the filter tank. In a diatomaceous earth filter the rinse cycle accomplishes the same task as in a sand filter, except during backwashing with DE filters, dirt, debris and some of the DE powder are removed. Rinsing after backwashing flushes out any remaining loose DE powder as well as other contaminants. Once a DE filter has been returned to the filter setting for a few minutes, new diatomaceous earth needs to be added and can be put in via the skimmer while the filter is still running.