Achieving proper media filter bed expansion during backwash in gravity filters is a crucial step in maintaining filter performance and longevity. The United States EPA and industry experts recommend filter bed expansion rates of 25 percent for anthracite and up to 50 percent for sand filters. Raven Environmental Products has developed a portable instrument, Filter Media Manager, to provide filter plants a simple and accurate way to measure expansion at multiple points in a filter. With the adjustable boom, measurements can be taken up to five feet from the sidewall.
Why is the amount of filter bed expansion important? Properly expanded media discharges dirt and debris and allows the individual grains of media to collide and scrub each other. The end result is increased filter life and performance capabilities.
Proper expansion drives consistent settling and good post backwash recovery. Improper expansion leads to reduced run times and mudballs that can cause short circuiting which makes the filter vulnerable to pathogen breakthrough.
A reasonable filter bed evaluation program includes periodic measurements that are logged in a worksheet. Consider marking four points in each filter, A B C D, that are used as measurement locations. Over time it will become evident if the filter is achieving consistent expansion throughout the filter.
Filter Media Manager utilizes a cable reel to deploy and retrieve an infrared sensor. A digital encoder measures media bed expansion and displays the result in inches or centimeters. There is no need for calibration. The unit can be mounted on round or square railings and used on all the plant’s filters. It is easy to move the unit throughout the filter and throughout the plant. WW
Raven Environmental Products offers a line of process control instrumentation that is engineered and manufactured in USA. To learn more, visit www.ravenep.com.
