Questions regarding the packing material for quartz sand filters
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As the title indicates, our company is replacing the quartz sand filler in a filter. The bottom layer consists of large particles measuring 2–4 mm and has a thickness of 200 mm; the middle layer is 300 mm high and contains particles of 1–2 mm in size; finally, the top layer is 500 mm high and made up of quartz sand particles with a size of 0.4–0.8 mm. My question is, what is the function of each layer respectively? Why use three layers? Isn’t it simpler to just use filler of the same specification? I would be extremely grateful if all of you experts could offer some guidance to me.
Our company uses this type of filter in several locations: the small particles on it are mainly used for filtering, but they tend to cause blockages easily； The lower layer is equipped with filters made of larger particles, which allow for backwashing when the filters become clogged; this arrangement is intended to extend the lifespan of the filters ；
A triangular distribution from small to large forms the filtering voids, facilitating reasonable distribution of filtration resistance and hydraulic distribution of backwashing water.
Question: I’m looking at other materials; it is said that larger particles are on the upper layer, but there are also claims that smaller particles are on the upper layer. Please help me figure this out
A proper grading ratio of the filter media can improve filtration efficiency and ensure uniform water distribution
All using fine particles results in more frequent backwashing, higher operating resistance, and low interception efficiency.