What is the flow requirement during the backwashing of a rapid rate sand filter per square foot?

The flow requirement during the backwashing of a rapid rate sand filter is typically in the range of 12-15 gallons per minute (gpm) per square foot of filter area. This range is essential to effectively dislodge and remove accumulated debris and contaminants from the sand bed, allowing the filter to restore its filtering efficiency.

Backwashing at this flow rate ensures that water is able to penetrate through the filter media with sufficient force to fluidize the sand and carry away impurities. If the flow rate is too low, the backwash may not adequately remove the accumulated materials, which could lead to decreased filter performance and clarity of the pool water. Conversely, if the flow rate is too high, it can disturb the sand bed excessively, leading to breakdown and improper functioning of the filter. Thus, the 12-15 gpm range strikes a balance that promotes proper cleaning and maintenance of the filter system.