The interior of the backwash sand filter tank adopts a double-layer structure. The upper part of the filter plate is the sand bed and the impurity storage space, and the lower part is the clean water circulation space. And there is a sewage outlet at the bottom of the tank, and the dirt deposited on the bottom of the tank can be removed from the bottom at any time.

The backwash sand filter uses quartz sand as a filter medium, and under a certain pressure, the water with high turbidity is filtered through a certain thickness of granular or non-granular quartz sand to effectively intercept. It is a water treatment equipment that removes suspended solids, organic matter, colloidal particles, microorganisms, chlorine, odor and some heavy metal ions in the water to clarify the water.

According to different water production, the filter needs to be equipped with quartz sand with different mesh (quartz sand particles of different diameters), which are all used for water treatment to remove turbidity, soften water, and pre-treatment of pure water.

As a filtering method in multi-media filter, backwash sand filter is often used together with activated carbon filter. Because the quartz sand filter can remove suspended substances, solid particles, suspended solids, and insoluble non-colloidal solid substances in water. The activated carbon filter can deodorize, decolorize, dechlorinate, remove organic matter, heavy metals, synthetic detergents, and radioactive substances.

he working principle of the backwash filter 

1. The backwash sand filter is filtered through the medium layer. The irrigation water source moves downward in the pores of the medium layer to isolate the impurities in the upper part of the medium layer, and the purified water enters the water outlet through the medium and the filter element, that is, the filtration of the irrigation water is completed.

According to the requirements of water consumption and filtration precision, sand and gravel filters can be used alone, or in combination or in series with other filters.

2. Filter recoil

Backwashing generally adopts a mechanical method, using water to flow upward from the lower part of the filter to flush up the dirt and discharge it through the sewage pipe. The time, frequency and water consumption of backwashing depend on the local water quality. When multiple sand and gravel tanks are used in combination, they should be backwashed one by one in turn until the pressure drop of the incoming and outgoing water meets the design requirements.

The filter media is automatically rearranged after backwashing, with larger particles at the bottom and small particles rising to the top. The backwashing of sand filter can be divided into manual backwashing and automatic backwashing.

3. Filtration precision

The backwash sand filter is a kind of media filter. The impurities removed by adding different media are different. For example, adding manganese sand and activated carbon can remove iron and manganese ions in water.

In irrigation water treatment filters, hard and wear-resistant quartz sand is often used as the filter medium. The filtration accuracy and filtration effect are determined by the size of the medium, the filtration rate and the thickness of the sand layer.

The finer the filter material, the higher the filtration precision, the smaller the flow rate and the greater the water resistance; the coarser the filter material, the lower the filtration precision, the greater the flow rate and the smaller the water resistance. At present, our company recommends the selection of quartz sand with a medium size of 2-4mm, which can effectively block particles larger than 150 meshes and impurities, and it is not suitable to use backwash sand and gravel filters to deal with particles larger than 200 meshes.