water sand filter

hi all

i know that it's not a plc related questions but i know that there are many of you have what i am looking for.
i have a project for retrofitting filter desks in a potable water treatment station and i am trying to find some information about the theory of operation for this filter in the web bur i didn't find any thing.
Any one have some documentation about what i need ?

Here are some places to get started:

http://www.fbleopold.com/water/filtration/filtration.htm

http://www.wef.org/applications/buyersGuide/results.cfm

http://ww.pennnet.com/search/search.cfm

A sand filter is a pretty simple device. Most filter suppliers provide their own controls for backwash and alarming.