The working principle of mechanical filters
Source：Jiangsu Envset Time:20 October 2020
Mechanical filters, also called pressure filters, are an important part of wastewater treatment systems. Next we will briefly introduce the working principle of mechanical filters.
The packing in the mechanical filter is made up of many refined quartz sands of different particle sizes in strict order from large to small, thus forming a good quartz sand gradation. When the filter is first put into use, the filtering effect is often not very good, because the filter did not form a "bridging" at the beginning. The so-called "bridging" refers to an interception net composed of suspended solids in the water, which intercepts The suspended matter with the same particle size will then intercept the suspended matter with smaller particle size, forming an inverse particle size filtration process that first intercepts large particulate matter and then small particulate matter.
Once the filter forms a "bridge", the filtering effect is very good. As the time of operation increases, the filtering accuracy becomes higher and the interception net becomes thicker and the inlet and outlet pressure difference becomes larger and larger, when the pressure difference reaches 1kg /cm2 The filter should be backwashed. In the process of backwashing, it is better to be equipped with compressed air to scrub the quartz sand. The general engineering experience is that the mechanical filter with a diameter of less than 2500mm does not need compressed air; and the machine with a diameter of more than 2500mm The filter must be scrubbed with compressed air to achieve a satisfactory cleaning effect; the backwash flow rate is generally 3-4 times the design capacity of the filter.
Old-fashioned mechanical filters mostly use large pebbles as the basic cushion, and the bottom is evenly punched with water-permeable holes with a convex steel plate, so that the water distribution is uneven, and it is easy to produce a large center filtration rate and a small edge filtration rate; the filter is backwashed At times, the phenomenon of mixed layer of quartz sand will occur, so that the filter material will inevitably leak into the downstream pipelines and precision filters, posing a serious threat to the precision filters and reverse osmosis devices.
After continuous practice and experimentation, many manufacturers have improved the mechanical filter. The water distribution device adopts a porous plate with a special form of ABS water cap. This type of ABS water cap has the function of different bidirectional output, that is, the output is small during operation. , The backwashing output power can be increased several times, so that the water distribution of the filter is more even when washing, and the backwashing is more thorough, and the water quality is greatly improved.
In order to prevent the fine sand filter during operation or backwashing, the penetration gap of this kind of ABS water cap is very small, generally around 0.1-0.2mm. It is worth noting that in the process of filling the filter filler, a certain amount of water must be injected into the filter to prevent the large quartz sand from breaking the ABS water cap; in the process of installing the water cap, you cannot wear hard shoes To prevent stepping on the ABS water cap. The mechanical filter is equipped with a backwash water inlet limit butterfly valve to control and adjust the backwash water flow. The backwash strength should expand the filter layer by 15-25%. The backwash compressed air strength is generally 10-18L/S.m2. If there is no compressed air, consider using Roots blower.
Jiangsu Envset provides advanced integrated wastewater treatment equipment and various wastewater treatment solutions. If you have any questions about the working principle of mechanical filters, you can contact us.
Tag: mechanical filters working principle, pressure filter