A _____ inch rise per minute in the filter is required to give a good backwash.

A rise of 25 inches per minute in the filter during backwashing is considered optimal for effectively cleaning the filter media. This value is based on industry standards that indicate sufficient velocity and agitation of the contaminants trapped in the filter.

When backwashing a filter, the goal is to dislodge and remove the accumulated particles and debris. The specified rise rate of 25 inches per minute ensures that water passes through the media at a speed capable of mobilizing the trapped particles without damaging the filter structure itself. It allows for the adequate expansion of the filter bed, facilitating the release of contaminants while ensuring that the media remains intact and functional for future filtration processes.

Higher or lower rates may not achieve effective cleaning; for instance, rates that are too high could damage the filter media or disrupt its layers, while rates that are too low might not dislodge the sediment effectively and could lead to poor filtration performance.