Water Sediment Filters are used to reduce or completely remove physical particles that are larger than a particular size from source water. Typical sediment filter is rated at 20 micron (ok), 10 micron (better), 5-1 micron (better yet) , or sub-micron (less than 1 micron, best but the slowest). A micron rating means that all particles larger than that will be trapped by a filter.
Water Filters for sediment removal come in many sizes and types, but generally fall into two types: Surface Filter Cartridges, and Depth Filter Cartridges.
Depth filters are the commonly seen as wound string, spun, or PP “melt-blown” cartridges that trap particles of larger size on the surface, and smaller particles under the surface down to the center core. Some depth filters, in fact, have what is called a "graded density" structure, meaning that the filter gets tighter as the water passes through the filter wall. Graded density filters remove particles of a variety of sizes. The outside catches big particles and the inside holds the smaller ones. As compared with pleated filters, they have a limited surface area, but they have the advantage of depth.
50 Micron Pleated Sediment Filter
Surface Filters are made in a thin sheet so that only the surface traps particles. These are commonly called "pleated filters" because of their accordion-shaped pleated structure. The pleated arrangement gives the filter surprisingly more surface area than depth filters. One of their great advantages is that they are washable and reusable, more so in large than small micron sizes.
5 Micron PP Melt Blown Filter for Sediment
For many uses with residential treatment virtually any filter style works well.
For example, a filter is marked “5 micron” is the traditional filter of choice as pre-filter for a residential reverse osmosis unit. It serves the purpose--protecting the carbon filter that follows it or the RO membrane from incoming dirt and debris--quite well. However, it can be replaced with virtually any good sediment filter--a melt blown or pleated filter works as well. You could replace it with a 10 micron filter or, if the water is clean, with a 1 micron filter and the RO unit would run fine in most situations.
Filter micron ratings for water are usually Nominal or Absolute. For sediment removal, nominal rated cartridges are more common. Absolute ratings are needed for example, in removing Giardia, a type of parasite, when it becomes important that the filter cartridge absolutely must be rated at 1 microns.
There are cases, however, where filters aren't interchangeable, and, as indicated, it's sometimes a matter of trial and error discovering what is perfect for the job you have. Often, changing from one style or from one micron rating to another dramatically affects performance. Some users "swear by" one style or another as the only thing that works well in their application.