Mechanical filters

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Mechanical cleaning of filters used for primary water removal from water and mechanical particle suspensions, such as clay, sand, silt, rust, etc. They should be installed before the water treatment devices for protection against contamination. For these purposes, use pre-filter (screen or disc) and fine filters with replaceable cartridges.

The use of two types of filters due to the fact that the excessive water pollution fine filters quickly become clogged and rough cleaning is not sufficient to protect the water treatment device from dirt. Functionally, there are two types of filters due to the fact that the grid filter can not provide sufficiently fine filtration therefore used for fine purification filter volumetric method. For the same rough treatment volumetric method is irrational because it is impossible to wash the filter element. Except Sediment filters are voluminous type, but they are more expensive and their use is advisable where the contaminant capacity of mechanical filters is insufficient.
An important parameter of the water strainer is a way to clean it, which determines how easy to use the filter, as well as its cost. According to a method of purifying filters are divided into:

· The filters with removable filter element (cartridge). Cartridges can be both disposable and reusable, cleaned manually.
· The wash filters. These filters after opening the drain valve at the bottom of the settled particles washed into drainage or outstretched tank and rinsed grid.
· Filters with manual backwash (not to be confused with cheaper washing filter). In these filters is an active filter mesh flushing backwash crank mechanism manually. The essence of backwash is as follows: when the washing water is not just the grid washes mechanical impurity, as it happens in washing filters and purifies the keeper, acting in the direction opposite to the filtration of water and thus pushing all mechanical impurities stuck between the cells.
· Semi-automatic backwash filters. These filters with manually opening the drain valve mechanism automatically rotates the backwashing. Such filters can be converted automatically by connection to the electronic control module.
· Automatic backwash filters. Such filters require no maintenance. Backwash occurs automatically at set intervals or pressure drop.

The quality and duration of the filtering of the filter depend on the quality of the grid and on the method of washing. Filter mesh made of stainless steel or polymeric materials. There are several ways to backwash. Some methods have been patented and are used only in specific filters manufacturers. We briefly describe the main ways:

· Rinse using a cleaning brush. Not the best, in our opinion, way. Cleaning quality deteriorates as the brush wear.
· In filters Honeywell (company Braukmann, Germany - USA) applying the method backwash mesh division into two parts. In normal mode, the lower water filters, are larger element. Filtering water passes from the outside inwards. In the washing process, the water flow passes through the upper portion of the mesh is cleaned, accelerated by the rotating turbine washes mesh inside the main portion, and capturing debris at the bottom of the flask is removed or outstretched tank or sewage system. During power mode backwash clean water continues to flow to consumers.

· The original method used in the backwash filters BWT companies and SYR (Germany). Backwash based on the principle of suction dirt with a special slotted element. During the flushing water flow creates a vacuum in the slot element, which is moving along the filter element, sucking mud. Applying suction element can achieve high differential pressures and effective washing of the particles. During rinsing, filtering is terminated as the 90% filter area remains free. This backwashing method is also the most restrictive of the grid, which allows the polymer filter element. It is elastic, so well cleaned by washing and, unlike the stainless steel is not affected by iron and chloride.

· We should also mention the Israeli filters Arkal. They filter element is a bundle of special discs made of plastics. The depth and width of the grooves applied to the disk, determines the minimum size of particles being filtered. Water passing from the outside inwards through the pack tightly compressed discs are cleaned of undissolved particles in it. Filter surface area is the sum of all disks included in the package. When washing the wheels unclenched, freeing detainees mechanical particles that makes them easy to wash off. This feature is a major advantage of the disc filters. However, these filters has a significant disadvantage. Over time, the wheels are deformed and filter quality deteriorates.

Divided into coarse and fine filters is rather arbitrary and depends on the application of filters. In the area of economic and clean drinking water filters can be considered rude by 90 microns and above. Thin - 20 microns and below. Filters between 20 and 90 microns can be considered "less thin" or "less harsh", depending on proximity to a given boundary. Apply filters to the bulk filtration for coarse (greater than 20 microns), in our opinion, wasted due to the need to replace the disposable cartridges. Grid cartridges usually cleaned with extraction of the filter housing or in the filter (backwash).
In the selection of filters to "dance" is necessary from the fine filter. Coarse filter placed only if the fine filter is clogged too quickly. The optimum combination of filters can only pick up empirically, since unknown absolute and relative amount and particle size of the contaminating water.