Filters usually have major equipment such as water inlets, water distribution systems, and sometimes devices for entering compressed air. Various necessary pipes and valves are provided outside the filter.
The mechanical filter is made of glass fiber reinforced plastic, stainless steel and carbon steel with anti-corrosion coating. The commonly used filter materials are: quartz sand, marble, anthracite, manganese sand and dolomite. The diameter of the particles is about 0.5- Between 1.5. A kind of filler can be filled in the filter and two or three fillers can be filled.
The operation of the filter is periodic, and each cycle can be divided into three steps: filtration, backwashing and washing.
The purpose of backwashing is to remove the dirt accumulated in the filter layer to restore the dirt intercepting capacity of the filter layer. It is an important step in the operation of the filter. In order to make the backwashing effect good, compressed air is usually supplied during backwashing.
The normal filter operates at a flow rate of about 8 to 10 m/h. When it reaches the allowable limit of the pressure drop across the water filtration layer, the filtration operation is stopped and the backwashing is started.
At this time, the water in the filter is discharged to the upper edge of the filter layer, and then the compressed air having a strength of 18-25 L/(m².S) is fed, and after being purged for 3 to 5 minutes, the air is continuously supplied. The backwash water is fed into the filter, and the strength thereof is such that the expansion ratio of the filter layer is about 40% to 50%. Finally, the water is passed down to the effluent before the official filtration operation begins.
This filter, in addition to the pressure drop through the filter layer to determine whether cleaning is required, can also be cleaned according to a certain running time. The permissible operating cycle should be obtained by adjusting the test. The filter should not always be cleaned when there is a suspension to pass through, and should be carried out slightly earlier, otherwise the filter layer is not easy to clean, and the filter material will agglomerate if it continues. A pressure drop of about 0.5 bar is generally allowed.