There are usually two main-lines in flats, those for hot and cold water. Therefore, a separate main-line filter is required for each type of water. Because hot-water filters operate under more severe conditions, more stringent requirements are imposed on them, and their cost is higher.
The productive capacity of main-line filters is determined by their size and by the mesh size of the filtering element. The hydraulic loss in the filter can range from 0.1 to 0.5 bar. It is particularly important to take this fact into account if the main-line pressure is low.
There are a lot of materials for main-line filter cartridges: grids, foamed or woven polypropylene, corrugated materials, windings. It is important to remember that cartridges intended for cold water are unsuitable for hot water, but cartridges intended for hot water are also suitable for cold water. Therefore, in main-line filters for cold and hot water in a flat you can use a single type of replaceable cartridge.
The majority of cartridges are disposable and are not subject to regeneration after the end of the service life. The world-only reusable cartridge for fine mechanical clearing of hot and cold water, Aragon 3, is produced by the Geyser Company.
The casing diameter corresponds to two standards: Big Blue (BB) and Slim Line (SL).
For the Big Blue (BB) standard, the diameter is 185 mm.
For the Slim Line (SL) standard, the diameter is smaller, 130–140 mm.
The majority of the filters used have a height of 10 or 20 inches.
The choice between these alternatives should be made taking into account the expected water consumption by the family: The larger the number of taps and water-consumption sites, the larger the size of the filter required. The SL standard is advisable for small water consumption, and the BB standard, for medium and large water consumption.